shifting the position of the eccentric that operates the cut off valve,
but it is usually done by means of moving the valve by a right and left
hand screw, such as shown in Fig. 3306. The cut off eccentric is set
ahead of the main eccentric, so that the cut off valve will close the
ports before the main valve would do so; thus, in the figure the cut off
valve is shown to have effected the cut off for port _a_ by the time the
main valve has fully opened port _a_, and is reversing its motion. If
the engine requires to reverse its motion, the cut off eccentric is set
exactly opposite to the crank, but otherwise, it may be set 8 or 10
degrees either ahead of or behind the crank, but if set too little ahead
of the crank, the port may reopen after the cut off has been effected.
[Illustration: Fig. 3307.]
Gonzenback's cut off valve is constructed as in Fig. 3307, the steam
chest having two compartments. A, A are the cylinder steam ports, C the
main valve, and E the cut off valve, whose ports (as G) are made wider
than the ports F.
Reducing the travel delays the point of cut off in the Gonzenback valve,
whereas in the common slide valve it gives an earlier cut off.
THE ECCENTRIC.
When a single eccentric is used, it is simply termed _the_ eccentric. If
a cut off valve (or two cut off valves) are used upon the engine, then
the eccentric that works the main valve is called the main eccentric,
while that which works the cut off valve or valves is called the cut off
eccentric. The main valve is that which works on the cylinder face; the
cut off valve is that which effects the cut off.
A shifting eccentric is one that is _moved across_ the shaft so as to
alter its amount of throw, and, therefore, the amount of valve travel,
the effect being to vary the point of cut off.
In engines where a constant amount of lead is given, or in other words,
when the eccentric position is intended to be fixed, the eccentric
should be secured to the crank shaft by a feather or key sunk into the
crank shaft so as to prevent the eccentric from moving, while enabling
it to be taken off and replaced without requiring any operations to
adjust its position with relation to the crank.
The feather should fit tight on the sides, as well as on the top and
bottom, and may have a slight taper on the sides, which will make it
easier to fit the featherway or keyway to the feather, and easier to put
the eccentric on or take it off.
By this means the eccentric cannot shift, and may be replaced after
being taken off without having to set the whole valve motion over again.
When the amount of valve lead or of compression is varied to suit the
speed at which the engine is to run, or to aid the counterbalancing of
the engine, a feather cannot be used because it will not permit the
eccentric to be moved to effect the adjustment.
Set screws possess disadvantages, inasmuch as that the point of the set
screw may leave an indentation, which, if the eccentric is moved a
trifle, may cause the set screw point to fall back into the old
indentation, thus rendering it difficult to make a small adjustment of
eccentric position.
[Illustration: Fig. 3308.]
An eccentric is the exact equivalent of a crank having the same amount
of throw, as may be seen from Fig. 3308, in which the outer dotted
circle represents the path of the crank and the inner one the path of
the centre of the eccentric. A small crank is marked in, having the same
throw as the eccentric has, and the motion given by this small crank is
precisely the same as that given by the eccentric whose outer
circumference is denoted by the full circle.
Considering the motion of both the crank and the eccentric, therefore,
we may treat them precisely the same as two levers, placed a certain
distance apart, revolving upon the same centre (the centre of the crank
shaft), and represented by their throw-lines.
[Illustration: Fig. 3309.]
In Fig. 3309, let the full circle E E represent an eccentric upon a
shaft whose centre is at C, and let the centre of the eccentric be at
_e_. The path of revolution of the eccentric centre will be that of the
dotted circle whose diameter is B, D. As the eccentric is in
mid-position (_e_ being equidistant from B and D), the valve will be in
mid-position as denoted by the full lines at the bottom of the figure.
Now suppose the eccentric to be revolved on the centre C, until its
centre moves from _e_ to V, its circumference being denoted by the
dotted circle A A, and if we draw from V a vertical line cutting the
line B, D at _f_, then from C to _f_ will be the distance the eccentric
would move the valve, which would then be in the position denoted by the
dotted lines at the bottom of the figure. It becomes clear then that if
we suppose the eccentric to have moved from mid-position to any other
position, we may find how much it will have moved the valve by first
drawing a circle representing the path of the centre of the eccentric,
next drawing a line (as B D) through its centre, and then drawing a
vertical line as (C _e_) through its mid-position and also a vertical
line from the eccentric centre in its new position, the distance between
these two vertical lines (as distance C _f_ in the figure) being the
amount the eccentric will have moved the valve.
It may have been noticed that the diameter of the eccentric does not
affect the case, the distance B D, or the diameter of the circle
described by the centre of the eccentric, being that which determines
the amount of valve motion in all cases. This being the case, we may use
the circle representing the path of the eccentric centre for tracing out
the valve movement without drawing the full eccentric, and the diameter
of that circle will of course equal the full travel of the valve.
[Illustration: Fig. 3310.]
The position of an eccentric upon a shaft is often given in degrees of
angle, which is very convenient in some cases. If a valve has no lap or
lead, the eccentric will stand at a right angle or angle of 90 degrees
when the crank is on the dead centre.
The division of a circle into degrees may be explained as follows:
Suppose we take a circle of any diameter whatever and divide its
circumference into 360 equal divisions, then each of these divisions
will be one degree. The number 360 has been taken as the standard, and
this being the case, there are 360 degrees in a circle, in a quarter of
a circle there will therefore be 90 degrees, because 90 is one quarter
of 360. By means of dividing a circle in degrees therefore we have a
means of measuring or defining any required portion of it.
In Fig. 3310 the degrees of a circle are applied for defining the
relative positions of a crank and an eccentric. As the zero position of
the crank is on a dead centre, it is so placed in the figure, while as
the zero position of the eccentric (which is for a valve having no steam
lap) is at 90 degrees from the crank, therefore the dotted circle
representing the path of the eccentric centre has its O or zero point at
90 degrees from the crank. Now suppose the eccentric centre stood at _v_
and the eccentric throw line at _c_ _v_, and it will stand at 30 degrees
from O, hence the angular advance of the eccentric is in this case 30
degrees, or in other words, it is 30 degrees in advance of its zero
position, or the position it would occupy when the crank is on the dead
centre and the valve has no lap and no lead.
If we measure the distance apart of the crank and the eccentric in
degrees, we find it is 120 degrees, hence place the crank where we may,
we can find the corresponding eccentric position because it is 120
degrees ahead of the crank. The sign for degrees is a small ° placed at
the right hand of the figures and slightly above them; thus, thirty
degrees would be written 30°.
FINDING THE WORKING RESULTS GIVEN BY A D SLIDE VALVE.
Although not strictly within the line of duty of an engineer or engine
driver, he is nevertheless sometimes called upon to find out how a valve
of given proportions will dispose of the steam, or what proportions to
give to a valve to accomplish certain results.
This is easy enough when either the travel of the valve or the amount of
the lap and the width of the port are given, but if the width of the
port alone is given, and all the other elements are to be found, it
becomes a more difficult problem.
An engineer, however, is rarely called upon to solve the question from
this stand-point, which properly belongs to the draughtsman or engine
designer.
If the amount of valve travel is given, however, all the other elements
may readily be found by the following construction:
[Illustration: Fig. 3311.]
Suppose that in Fig. 3311 a D valve is to be designed to cut off the
steam when the piston has travelled from position B´ to R´, or at
three-quarters of its stroke. Then to find the position the crank pin
will be in when the cut off occurs, we draw a circle, B D, representing
the path of the crank on the same scale that the length of the piston
stroke is represented. The straight line from B to D will, therefore,
represent the piston stroke without drawing the piston or cylinder at
all (this being done in the figure to make the explanation clear). When
the crank is on its dead centre, B, the piston, will be at B´, and the
valve in the position shown (supposing it to have no lead). As soon as
the crank and valves begin to move, the steam will enter steam port _a_,
and to find where the crank will be when the piston is at three-quarters
stroke, and is, therefore, in position R´, we mark a point at R
three-quarters of the distance from B to D. Then, taking no account of
the length of the connecting rod, we draw a vertical line Y from R to
the circle, and this line gives at H the position the crank will be in
when the piston is at R. We have so far, therefore, that while the
piston travels from B´ to R´, the crank will travel from B to H. Now, it
will be found that if we set a pair of compasses from B to F, which is
half-way from B to H, and then rest the compasses at D, and mark an arc
V, then a line from V to the centre of the crank will give us the proper
position of the eccentric. As the centre of the crank pin and also the
centre of the eccentric both travel in a circle, we may, therefore, take
a circle having a diameter equal to twice the throw of the eccentric,
(or, what is the same thing, equal to the full travel of the valve), and
let it represent the paths of both the eccentric centre and the crank
pin centre, the latter being drawn to a scale that is found by dividing
the length of the piston stroke by the travel of the valve; thus, if the
travel is 3 inches and the stroke 30 inches, the diameter of a 3 inch
circle will represent the valve travel full size, and the piston stroke
one-tenth full size, because 30 ÷ 3 = 10. It has been shown on page 376
that the length of the connecting rod affects the motion of the piston
by distorting it, and it is necessary to take this into account in
constructing the actual diagram, which may be done as follows:
The valve travel and point of cut off being given, to find the required
amount of lap, there being no lead, draw a circle equal in diameter to
the travel of the valve, and draw the line of centres B D, Fig. 3312;
mark on the line of centres a point R, representing the position the
piston is to be in at the time the cut off is to take place.
Set a pair of compasses to represent the length of the connecting rod on
the same scale as the circle B D represents the path of the crank; thus,
if the connecting rod is three times the length of the stroke, the
compasses would be set to three times the diameter of the circle B D.
[Illustration: Fig. 3312.]
A straight line from B to D and passing through the centre C of the
crank will represent the line of centres of the engine, which must be
prolonged to the right sufficiently to rest the compasses on it and draw
the arc Y, which will give at H the position of the crank when the
piston is at R, and the cut off is to occur.
We have thus found that the amount of circular path the crank will move
through from the dead centre to the point of cut off is from B to H, and
as the eccentric is fast upon the same shaft, it will, in the same time,
of course, move through the same part of a circle.
One half of its motion will be to open and one half to close the port,
so that we may by means of the arcs at F get the point F, which is
midway between B and H, and with the compasses set from B to F, mark
from D the two arcs V and V´ whose distance apart will obviously be the
same as from B to H.
Then from V to V´ draw the line P, and from this line to the centre C of
the crank shaft is the amount of steam lap necessary for the valve,
while from this line (P) to D is the width of the steam port.
The proof of the diagram is as follows:
When the crank is on the dead centre, the centre of the eccentric is at
V, its throw line being represented by the line from V to C, and the
valve is about to open the port as shown in the figure.
While the eccentric is moving from V to D, the valve will move in the
direction of the arrow and will fully open the port, while the crank pin
will move from B to F.
Then, while the crank moves from F to H, the eccentric will have moved
the valve to the position it occupies in the figure, having closed the
port and effected the cut off.
We have here found the amount of lap and the position of the eccentric
necessary for a given point of cut off when the latter is given in terms
of the piston stroke. If, however, the point of cut off had been given
in terms of the crank pin position, we might find the required amount of
lap at once, by simply drawing a line from the centre B, the point to H
where the crank pin is to be when the cut off occurs.
From this line we could then draw the dotted circle G, and just meeting
the line P, which would give the eccentric position.
To find the piston position, the arc Y would require to be drawn by the
same means as before.
[Illustration: Fig. 3313.]
[Illustration: Fig. 3314.]
If the valve is to have lead, the diagram may be constructed as in Fig.
3313, in which the circle has a diameter equal to the travel of the
valve and the cut off is to occur when the piston is at R and the crank
at H.
When the valve is at the end of its travel and has fully opened the
port, the eccentric will be at D, hence from D we mark an arc G distant
from D to an amount equal to the width of the steam port, drop the
vertical _m_ from G, and at its lower end V´ is the position of the
eccentric centre at the point of cut off. Then draw a line P, distant
from _m_ equal to the lead, which will give at V the position of the
eccentric when the crank is on the dead centre, and the valve is open to
the amount of the lead. The lap is obviously the distance from the
centre C of the crank shaft to the arc G.
We have here found all the points necessary except the point at which
the valve will open the port for the lead, and this we may find by
setting a pair of compasses to the radius B H (or to radius V V´, as
both these radii are equal), and from V as a centre, mark at A an arc,
which will give the crank pin position at the time the port first opens
for the lead, or in other words it will give the position. The proof of
the construction is, that if we set the compasses to the distance
between the crank pin position on the dead centre and the point of cut
off (or from B to H), we may apply the compasses to the points V, V´,
which represent the eccentric position when the port is opened to the
amount of the lead, and when the cut off occurs.
If the point of cut off only is to be found, we mark from C, Fig. 3314,
an arc G representing the amount of valve lap and arc S representing the
lead. A vertical P gives the eccentric position V when the crank is on
the dead centre at B, and a vertical _m_ from G gives at V´ the
eccentric position at the point of cut off. Then with the compasses set
to the points V V´, we may mark from B an arc, locating at H the
position of the crank at the point of cut off, and from this with
compasses set to represent the length of the connecting rod on the same
scale as the circle represents the path of the crank, we may, from a
point on the line of centres, mark an arc Y giving at R the piston
position at the point of cut off.
When, therefore, the lap is given, we mark it from the center C of the
crank shaft, and find the other elements from it, whereas, when the lap
is to be found, we mark the width of the port from the end D of the
valve travel, and find the other elements from that.
A proof of all the constructions is given in Fig. 3314, in which the
letters of reference correspond to those in the previous figures, and
the positions of the parts are marked in degrees of angle.
To find the piston position at the point of cut off, measured in inches,
of the piston stroke it must be borne in mind that as the circle B D
represents the full travel of the valve, the diagram gives all the
positions of the eccentric and valve full size, but that as it
represents the crank path on a reduced scale, therefore we must multiply
the measurement on the diagram by that scale.
Suppose, for example, that the piston stroke is 10 inches, and the valve
travel 2-1/2 inches, and the circle being 2-1/2 inches in diameter, is,
when considered with relation to the eccentric motion, full size, but
when considered with relation to the piston or crank motion, it is only
1/4 the size, hence to find the piston position at the time of cut off,
we must multiply the distance from B to R by 4.
[Illustration: Fig. 3315.]
LINK MOTION FOR STATIONARY ENGINES.
The ordinary mechanism employed to enable a stationary engine to be
reversed or run in either direction is the Stephenson link motion. Other
forms of link motion have been devised, but the Stephenson form has
become almost universal.
[Illustration: Fig. 3316.]
Fig. 3315 represents this link motion or reversing gear with the parts
in position for the full gear of the forward motion, and Fig. 3316
represents it in full gear for the backward motion.
The meaning of the term full gear is that the parts are in the position
in which the steam follows the piston throughout the longest or greatest
part of the stroke. When in full gear the link motion operates the valve
almost precisely the same as if the eccentric rod was attached direct to
the valve spindle and no link motion was used.
Besides enabling the engine to run in both directions, however, the link
motion provides a means of reducing the amount of valve travel and thus
causes the live steam to be cut off earlier in the piston stroke, thus
using the steam more expansively. This is done by moving the reversing
lever more upright, the earliest point of cut off being obtained when it
is upright and the latch is in the notch marked O on the sector in Fig.
3315. If with the engine standing still we move the link motion from
full gear forward to full gear backward and watch the valve, we shall
find that the valve lead increases as the reversing lever approaches the
upright position, or mid gear as it is termed, and that after passing
that point it gradually diminishes again, the valve being so set that
the lead is the same for full gear forward as it is for full gear
backward.
The reversing lever is used to move the link into the required position
and to hold it there (the end of the latch fitting into the notches in
the sector being the detaining or locking device); as the link is
suspended by its saddle pin S and the link hanger, therefore its motion
is to swing or partly rotate on the pin S, and at the same time ending
in the arc of a circle whose centre of motion is in the pin at the upper
end of the link hanger which is pivoted to the lower arm of the lifting
shaft (which is sometimes termed the tumbling shaft). It will clearly be
seen that with the position the parts occupy in Fig. 3315, and the crank
motion being in the direction of the arrow, the forward eccentric will
move the top of the link to the right and therefore the valve will move
to the right, while the backward eccentric will move the bottom end of
the link to the left.
In full gear, however, the bottom eccentric rod has but a very slight
effect indeed on the motion of the valve because both the link hanger
and the link block will permit the link to swing on centre of the link
block pin as a pivot. If now we turn to Fig. 3316 for the full gear
backward, we shall see that these conditions are reversed and the
backward eccentric becomes the effective one, being in line with the
valve spindle. By shifting the link from one gear to the other,
therefore, we have merely changed the direction in which the link will
move the valve, and, therefore, the direction in which the engine would
run.
In Fig. 3315 for the full gear the parts are shown in position, with the
piston at the crank end of the cylinder, and the crank pin on the dead
centre, and the eccentrics must be set as shown in the cut, the
eccentric rods being open and not crossed. When, however, the crank is
on the other dead centre and the piston at the head end of the cylinder,
the rods will cross each other, and it is necessary to remember that the
rods should be open when the piston is at the crank end of the cylinder.
If, however, the running gear contains a rock shaft, or rocker (as is
the case in American locomotives), then these conditions are reversed,
and the eccentric rods will cross when the piston is at the crank end of
the cylinder.
In setting the slide valve of an engine having a link motion, there are
two distinct operations. First, to put the crank on the respective dead
centres, which will be fully described on page 394 and need not be
repeated; and second, to set the eccentrics in their proper positions on
the shaft, and correct, if necessary, the lengths of the eccentric rods.
The crank being on the dead centre, with the piston at crank end of the
cylinder, the eccentric should be moved around on the shaft by hand
until there is the desired amount of lead at the crank end port, and
temporarily fastened there, a set screw usually being provided (in the
eccentric) for this purpose. The lead is best measured with a wedge, W,
Fig. 3315. The crank is then put on its other dead centre, and the lead
for the head end port is measured. If the lead is to be made equal for
the two ports (as is usually the case in horizontal engines) and it is
found to come so, the valve setting for the forward gear is complete. If
the lead is not equal, the forward eccentric rod or else the valve
spindle must be altered so as to make the lead equal. In some engines
adjusting screws are provided for the purpose of regulating the length
of either the eccentric rod or else of the slide spindle; it does not
matter which is altered. The link motion is then put in full gear for
the backward motion, and, with the crank on the dead centre (it does
not matter which dead centre), the eccentric is moved by hand upon the
crank shaft until there is the required amount of valve lead. The
eccentric is then fastened on the shaft and the crank put on the other
dead centre, and the lead tried for the other port, and made equal by
lengthening or shortening the backward eccentric rod. It is to be noted
that altering the length of the eccentric rod or of the valve spindle
makes it necessary to reset the eccentric, as it affects the amount of
lead at both ports; hence, if any alteration of rod length is made, the
whole process here described must be repeated after each alteration of
rod length.
FLY BALL OR THROTTLING GOVERNORS.
An isochronal governor is one in which the two opposing forces are equal
throughout the whole range of governor action, or, in other words,
equal, let the vertical height of the plane in which the balls revolve
or swing be what it may.
A dancing governor is one that acts spasmodically. Such an action may
occur from undue friction in the parts of the governor or of its
throttle valve.
The friction offers a greater resistance to starting the parts in motion
than it does to keep them in motion after being started; hence, the
parts are apt to remain at rest too long, and to move too far after
being put in motion.
Rule to find the number of revolutions a governor should make. Divide
the constant number 375.36 by twice the square root of the height of the
cone in inches. The quotient is the proper number of revolutions per
minute.
_Example._--A governor with arms 30-1/2 inches long, measuring from the
centre of suspension to the centre of the ball, revolves, in the mean
position of the arms, at an angle of about thirty degrees with a
vertical spindle forming a cone of about 26-1/2 inches high. At what
number of revolutions per minute should this governor be driven? Here
the height of the cone being 26.5 inches, the square root of which is
5.14 and twice the square root 10.28, we divide 375.36 by 10.28, which
give us 36.5 as the proper number of revolutions per minute at which the
governor should be driven.
The construction of the Pickering governor is as follows:
[Illustration: Figs. 3317, 3318.]
In Fig. 3317 it is shown in its simplest form, and in Fig. 3318 with the
driving pulley and speeder (or engine speed regulating device) attached.
This speeder consists of a spiral spring whose tension may be adjusted
to more or less resist the rise of the governor balls, and thus enable
the engine to run at a greater speed for a given amount of rise of the
governor balls, hence by increasing the tension the engine speed is
increased.
THE SPRING ADJUSTMENT.
The adjustment of the spring tension is made by a worm actuating a worm
wheel on a rod passing through the spring, and to which one end of the
spring is attached, the other acting on an arm that projects into a slot
in the governor spindle. It is obvious that the speeder can be adjusted
while the engine is running.
[Illustration: Fig. 3319.]
In Fig. 3319 the governor is shown with the speeder and Sawyer's valve,
the latter enabling the governor valve to be opened or closed without
affecting the rise and fall of the governor balls, which is done by
operating the arm shown on the right, whose ends are provided with
loops, so that a cord may be attached, enabling the engineer to operate
the governor from a distance.
The safety stop or stop motion is shown on the right, Fig. 3320.
It acts to close the governor valve and stop the engine in case the belt
that drives the governor should get off the pulley or break. This stop
motion consists of a pulley suspended by a rod, and riding on the belt
which supports its weight. Should the governor belt break, this pulley
falls and severs the connection between the valve and the governor,
closing the valve, and holding it closed. Fig. 3321 shows the governor
in section to expose the construction of the valve. The valve V is what
is termed a poppet or poppet valve, which is balanced, because the steam
entering at I, and taking the course denoted by the arrows, acts equally
on both ends of the valve and does not press it in either direction,
while as the steam surrounds the valve it is not pressed sideways.
At B is a gland or stuffing box to keep the spindle or rod steam-tight.
At A is the slot for receiving the arm from the speeder and from the
stop motion.
P is obviously the driving pulley, imparting motion to the bevel wheels
G, which drive the outer spindle S, the inner spindle _s´_ being
connected to A. The balls are upon ribbon springs D, which are secured
at their lower ends to a link fast to the spindle S.
The centrifugal force generated by the balls causes them to move
outwards, their upper ends pulling down the cap to which they are
secured, and this cap operates the valve.
Governors of this class are sometimes termed _fly-ball_ governors.
STARTING A PLAIN SLIDE-VALVE ENGINE.
The method to be pursued before starting a plain slide-valve engine
depends upon what the engineer knows about the condition of the engine.
If he knows the engine is in proper running order, all that is necessary
is to first attend to the oil cups and start them feeding.
Then, if it is necessary, move the crank into the required position to
start it easily; open the waste water cocks to relieve the cylinder of
the water that will be condensed from the steam when it enters a cool
cylinder, and turn on the steam; giving the throttle valve enough
opening to start the engine slowly.
The best position for the crank pin to be in to enable its starting
easily is midway between the horizontal and vertical position (or, in
other words, at an angle of 45° to the line of centres) and inclining
toward the cylinder, so that when the engine moves the piston will
travel toward the crank shaft.
There are two reasons why this is the best position for starting. The
first applies to all engines because there is a greater piston area for
the steam to act on when the piston is moving toward the crank than
there is when it is moving away from it. This occurs because the piston
rod excludes the steam from a part of the face of the piston. The second
applies to all plain slide-valve engines whose slide valves have equal
laps and both steam ports of equal widths, because the live steam
follows further on the stroke when the piston is moving toward the crank
than it does when it is moving away from it, and it follows that more
piston power is developed, and the engine is less likely to stop when
passing the dead centre.
[Illustration: Fig. 3320.]
[Illustration: Fig. 3321.]
When first taking charge of an engine, it is proper, before starting it,
to ascertain that it is in fair working order.
A complete examination of an engine should include a test of the fit of
the piston to the cylinder bore, of the cross head to the guide bars, of
the connecting rod brasses to the crank pin and cross head journals, and
of the crank shaft to its bearings. It would also include a testing of
the alignment of the crank shaft and of the guide bars, as well as the
set of the valves and the adjustment of the governor.
The least examination permissible with a due regard to safety would be
to move the engine throughout at least one full revolution by hand, and
to see that the connecting rod brasses and the main bearings do not fit
too tight to their respective journals, and to then start the engine
slowly by giving it only enough steam to move it, keeping the hand on
the throttle valve so as to be able to shut off steam instantly should
it become necessary.
A thorough examination should be made in the following order:
First, slightly loosen the nuts on the crank shaft bearings and also the
connecting rod keys.
Then move the fly wheel around until the crank points straight to the
cylinder, which will bring the piston up to the outer end of the
cylinder bore.
Take off the cylinder cover and also the follower from the piston head,
and see that the piston rings are set out to fit the cylinder bore but
not to bind it tight. Then bolt the follower up firmly in place again.
Take off the connecting rod and move the piston until it touches the
cylinder cover at the other or crank end of the cylinder, and then draw
a line across the side face of the cross head guide and on the guide
itself.
Put on the cylinder cover and push the piston back until it abuts
against it, and then make another line on the cross head guide and the
guide bar, and these two lines will show the extreme positions to which
the piston can be moved when the connecting rod is disconnected.
Next put on the connecting rod, carefully adjust the keys or wedges, so
that the bores of the brasses fit easily to the crank pin and cross head
pin, seeing that the oil holes are clear, and that oil will feed
properly to the journals.
In making this adjustment it is a good plan, if there is any end play of
the brasses on the crank pin, to set up the key or wedge until the rod
can just be moved by hand on the pin, by first pulling the rod to one
end of the pin, and then pushing it to the other.
In putting on the rod, it will be necessary to move the piston a trifle
towards the crank.
In making the adjustment of the crank pin fit to the rod brasses, it is
a good plan to drive the key home until the brasses are known to bind
the crank pin, and then mark a line across the side face of the key and
fair with the top face of the connecting rod strap, to then slacken back
the key enough to ease back the brasses to a proper fit, and then mark
another line on the key.
The first line will form a guide as to how much to slacken back the
brasses to adjust the fit, and the second one will form a guide as to
how much the key is moved when making a second adjustment, if one
should be found necessary after the engine has been running.
Similarly in adjusting the main bearing boxes to the crank shaft, either
the nuts, or what are called leads, may be taken to adjust the fit.
Leads are necessary when the joint faces of the brasses do not meet, but
are left open so that the wear can be taken up while the engine is
running.
It is better, however, to let the brasses abut together, so that it may
be known that the fit is correct when the nut is screwed firmly home.
The method of taking a lead is as follows: The top brass is loosened,
and between the joint faces of the brasses or boxes on each side of the
shaft a piece of lead wire is inserted. For a shaft of, say, four inches
in diameter, the lead wire will be about 7/16 inch in diameter, or for a
10 inch shaft the wire should be 1/8 inch in diameter, and should be as
long as the brass. The nuts are then screwed firmly home, and the wire
will be squeezed between the brasses and thus flattened on two opposite
sides, the thickness showing how far the joint faces of the brasses are
apart when the bore grips the journal.
A liner, fit strip, distance piece, or shim (all these names meaning the
same thing) is a strip of metal placed between the joint faces of the
brasses to hold them the proper distance apart to make a working fit of
the journal and brasses, when the latter are firmly bolted up.
The fit of the top brass therefore depends upon the fit strip being of
the proper thickness from end to end.
Now the lead wire is the gauge for the thickness of the fit strip, the
latter being made a trifle thicker than the flattened sides of the lead.
If the lead is thicker one end than the other, or if one lead is thicker
than the other, the fit strips must be made so, and the leads must be
marked so that it may be known which way they were placed between the
brasses so that the proper fit strip may be on the proper side of the
brass, and the proper end towards the crank.
Another method that is adopted in the case of large brasses is to screw
down the nuts until the brasses bind the journal, and then make a mark
on the nut and on the bolt thread. The nut is then slackened back as
much as the judgment dictates, and a note made of how much this is, the
marks forming a guide.
As the wear takes place, and the nuts screw farther down, a new mark is
made on the nut, so that it may always be known how much to screw up or
unscrew the nut, to make a light adjustment.
To avoid heating, it is a good plan to press some tallow into the bottom
or in one corner of the oil cup, and then pour in the oil used for
ordinary lubrication. So long as the bearing remains cool, the oil will
feed and the tallow remain.
If the bearing heats, the tallow will melt, and, having a heavier body,
will give a more suitable lubrication.
To find if the connecting rod is of the right length to give, as it
should do, an equal amount of clearance (or space between the piston and
the cylinder cover) at each end of the stroke, move the fly wheel a
trifle in either direction, and then move it back until the crank is on
the dead centre, and draw a line across the cross head guide and guide
bar, and the distance between this line and that drawn when the
connecting rod was disconnected, shows the amount of clearance at that
end of the cylinder. Then move the crank pin over to its other dead
centre, and mark a line across the cross head guide and the guide bar,
and the distance between this line and that drawn before the connecting
rod was put on will show the clearance at this end of the cylinder.
If the clearance is not equal for the two ends, it should be made so by
putting liners behind the connecting rod brasses so as to lengthen or
shorten the connecting rod (according as the case may require), and
equalize the clearance, while at the same time bringing the connecting
rod keys up to their proper heights.
To test the set of the valve, the steam-chest cover must be taken off,
the crank placed alternately on each dead centre, and the lead measured
for each port.
An unequal or an equal degree of valve lead may be given by suitably
altering the length of the eccentric rod, but when the lead is equal for
the two ports, its amount must be regulated by moving the position of
the eccentric upon the crank shaft.
SQUARING A VALVE.--A method not uncommonly pursued in setting a valve is
to what is called _square it_ before trying it.
This squaring process consists in so adjusting the length of the
eccentric rod that the valve travels an equal distance over or past the
steam edge of each steam port; but since the valve does not, when set to
give equal lead, travel equally past each port, therefore the work done
in squaring a valve is all thrown away, and may result in altering the
eccentric rod from its proper length to an improper one, necessitating
that it be altered back again in order to set the lead right.
The proper method is to adjust both the length of the rod and the
position of the eccentric, by testing the lead at once, lengthening the
eccentric rod to increase the lead at the crank end, or vice versa.
Each alteration of eccentric position may render necessary an alteration
of rod length, or vice versa, each alteration of rod length may render
it necessary to alter the eccentric position, hence the lead should be
tried at both ends of the cylinder after each alteration of either rod
length or eccentric position.
In vertical engines the weight of the crank shaft causes it to wear the
bottom brass or part of the bearing box the most, thus lowering its
position, while the eccentric straps and pins wear most in the same
direction; hence the wear increases the lead at the head end of the
cylinder when the latter is above the crank, and at the crank end when
the crank is above the cylinder.
When the cylinder is above the crank, the weight of the piston, cross
head and connecting rod is counterbalanced at the end of the downward
piston stroke by giving the crank end port more lead; but when the
cylinder is below the crank, it is the head end port that must be given
increased lead to prevent a pound or knock, or to allow for the wear
downwards of the parts.
After an engine is started, the pet cocks should (if they are not
automatic) be closed as soon as dry steam issues, and if this cannot be
seen, it may be assumed to occur after the engine has made about 20
revolutions.
The parts that will then require particular attention are the crank pin,
main bearings, cross head guides and the pump, if there is one. The
former must be kept properly lubricated, so that they may not get hot
and the cylinder lubricator (which is usually placed on the steam pipe)
must be set to self feed properly.
If the crank shaft bearings should begin to heat, loosen the cap bolts
and lubricate more freely, or, if it is at hand, some melted tallow may
be applied with the oil, as a heavier lubricant may stop the heating.
The crank pin requires the most attention and is the most difficult to
keep cool and to examine, because of its circular path rendering it
difficult to feel it. This may be done, however, in two ways, first by
standing at the end of the engine bed and gradually extending the hand,
until the end of the rod meets it as it passes, and, second, by placing
the hand on the connecting rod as near to the end of the guide bar as
possible where its motion is diminished and moving the hand towards the
crank pin, by which means the end of the crank pin may be approached
gradually.
If the end of the rod is hot, the engine speed should be reduced or the
engine should be stopped so that the connecting rod key or wedge may be
eased back and the oil feed made more copious. Then, after the engine
has been stopped for the night, the brasses should be taken out and any
rough surface, either on the brasses or on the pin, smoothed down with a
file.
Hot crank pins may occur from several causes, but by far the most common
ones are from improper oiling, or from the engine being out of line.
A heavier oil will often stop, or at least modify, the heating, but its
cause should always be discovered and remedied.
Engines that are used out of doors or are exposed to temperatures below
the freezing point must be left so that steam leaks may not condense in
any of the parts or pipes and burst them.
Leaky throttle valves may, for example, cause water to accumulate in
the steam chest and freeze, perhaps bursting the steam-chest cover.
To prevent this let the engine stand with the crank just past the dead
centre, so that the steam port will be open, and open the waste water
cocks on the cylinder, and also on the steam chest if there is any.
If the cylinder is jacketed all the drain cocks for the jacket should
also be opened.
A leaky check valve may cause the steam to condense in the pump and
freeze it up solid or burst it or the pipes. To avoid this, open the
pump pet cock.
Open all the drain cocks on the heater and water pipes.
If the water is left in the boiler all night it is liable to freeze.
To prevent this leave a well banked fire.
In extreme weather remember that on exposed engines the oil, if of such
quality as sperm or lard oil, may freeze and prevent feeding until the
bearings get hot and melt the oil.
To prevent this use a lighter oil, as, for example, a mineral oil. Or,
in case of freezing, melt the oil in the cups with a piece of wire made
red hot while getting up steam in the morning.
A good plan to prevent oil from freezing and yet have a good quality of
oil is to mix two parts of lard oil with one part of kerosene.
Portable engines should stand as nearly level as possible, so that the
water will stand level above the tubes and crown sheet of the fire box.
When feed water is drawn from a natural supply, as from a stream, the
strainer at the end of the suction pipe should be clear of the bottom of
the stream, where it is liable to be choked.
When the exhaust steam is used to feed the boiler, do not open the valve
that lets the exhaust steam into the feed-water tank until a little
while after the engine has started, because the oil fed to the cylinder
will otherwise pass into the feed tank and may cause priming.
In engines having plunger pumps for feeding the boiler it is essential
to keep the plunger properly packed, as a leak there impairs or stops
the pump from acting.
A gauge glass may be cleaned when the engine is cold by shutting off the
cocks leading from the boiler and filling the glass with benzine,
allowing it to stand two hours; the benzine must be let out at the
bottom of the glass tube, and not allowed to enter the boiler.
In starting a new engine be careful to let the bearings be slightly
loose.
At first give only enough steam to just keep the engine going, and keep
the hand on the throttle valve ready to shut off steam instantly if
occasion should require.
PUMPS.
Pumps are divided into the following classes:
Lift pumps, in which the water flows freely away from the pump, which
performs lifting duty only.
Force pumps, which deliver the water under pressure.
Plunger pumps, in which a "plunger," or "ram," as it is sometimes
termed, is used.
Piston pumps have a piston instead of a plunger.
A double acting pump is one in which water enters into and is delivered
from the pump at each stroke of its piston or plunger, or, in other
words, one in which, while water is being drawn in at one end of the
pump, it is also being forced out at the other.
A single acting pump is one in which the water enters the pump barrel
during one piston or plunger stroke, and is expelled from the pump
during the next stroke, hence the action of the suction and of the
delivery is intermittent, although the pump is in continuous action.
For very heavy pressures plunger pumps are generally used, the plunger
being termed a _ram_.
The advantage of the plunger or ram is that it gives a positive
displacement, whereas in a piston pump a leaky piston permits the water
from the suction side to pass through the leak in the piston, to the
delivery side.
Piston pumps possess the advantage that there is less difference between
the contents of the pump and the displacement than is the case in
plunger pumps.
The displacement of a piston pump is found by multiplying the area of
the pump bore by the length of the piston stroke.
The displacement of a plunger pump is less than the above, by reason of
there being a certain amount of clearance or space between the
circumference of the plunger and that of the cylinder bore.
It is desirable to keep the clearance space in all pumps as small as the
conditions will allow, especially if the pump is liable to lose its
water.
Losing the water means the falling of the suction water back into the
source of supply, which may occur when the engine has to stop
temporarily, and there is a leak in the suction valves.
[Illustration: Fig. 3322.]
Rotary pumps are those in which the piston revolves, an example of the
most successful form of rotary pump being shown in Fig. 3322, which is
that used by the Silsby fire engine.
The advantage possessed by a rotary pump is that it keeps the water
passing through the suction in a continuous and uniform stream, as it
has no valves.
It may therefore be run at a high velocity or attached direct to the
engine shaft.
If a rotary pump leaks, the efficiency is not impaired so much as in a
piston or plunger pump, all that is necessary being to run the pump at a
high speed.
[Illustration: Fig. 3323.]
The principles of action of a pump may be understood from Fig. 3323,
which represents a single acting plunger pump shown in section, and with
the suction pipe in a tank of water, the pump being empty.
The surface of the water in the tank has the pressure of the atmosphere
resting upon it, and as the pump is filled with air, the surface of the
water within the pipe is also under atmospheric pressure.
Now suppose the plunger to move to the right, and as no more air can get
into the pump, that already within it will expand, and will therefore
become lighter, hence there will be less pressure on the surface of the
water within the suction pipe than there is on the outside of it, and as
a result the water will rise up the pipe, not because the plunger draws
it, but because the air outside the pipe presses it up within the pipe.
[Illustration: Fig. 3324.]
The water inside the pipe will rise above that outside in proportion to
the amount to which it is relieved of the pressure of the air, so that
if the first outward stroke of the plunger reduces the pressure within
the pump from 15 lbs. to 14 lbs. per square inch (15 lbs. per square
inch being assumed to be its normal pressure), the water will be forced
up the suction pipe to a distance of about 2-1/4 feet, because a column
of water an inch square and 2-1/4 feet high is equal to 1 lb. in weight.
In Fig. 3324 the pump plunger is shown to have moved enough to have
permitted the water to rise above the suction valve, and it will
continue to rise and enter the pump barrel as long as the plunger moves
to the right.
When the plunger stops, the suction valve will fall back to its seat and
enclose the water in the pump; but as soon as the plunger moves back to
the left hand and enters the barrel pump further, the delivery valve
will rise, and the plunger will expel from the pump a body of air or
water equal in volume to the cubical contents of the plunger, or rather
of that part of it that is within the barrel, and displaces water.
If the plunger was at the end of its first stroke to the right and the
pump half filled with air, then this air will be expelled from the pump
before any water is; whereas if the pump was filled with water, the
latter only will be delivered.
Now suppose the first plunger stroke reduces the air pressure from 15 to
14 lbs., and that the second drawing stroke of the plunger reduces the
air pressure in the pipe to 13 pounds per inch, the water will rise up
it another 2-1/4 feet, and so on until such time as the rise of a column
of water within the pipe is sufficient to be equal in weight to the
pressure of the air upon the surface of the water without; hence it is
only necessary to determine the height of a column of water that will
weigh 15 lbs. per square inch of area at the base of the column to
ascertain how far a suction pump will cause water to rise, and this is
found by calculation or measurement to be a column nearly 34 feet high.
It is clear then, that however high the pump may be above the level of
the water, the water cannot rise more than 34 feet up the suction pipe,
even though all the air be excluded from it and a perfect vacuum formed,
because the propelling force, that is, the atmospheric pressure, can
only raise a column of water equal in weight to itself, and it is found
in practice to be an unusually good pump that will lift water thirty
feet.
[Illustration: Fig. 3325.]
Fig. 3325 shows the plunger making a delivery stroke, the suction valve
being closed, and the delivery valve open where it will remain until the
plunger stops.
To regulate the quantity of water the pump will deliver in cases where
it is necessary to restrict its capacity, as in the case of maintaining
a constant boiler feed without pumping too much water in the boiler, the
height to which the suction valves can lift must be restricted, so as to
limit the amount of water that can enter the pump at each drawing
stroke.
The delivery valve should lift no more than necessary to give a free
discharge without causing the valve to seat with a blow; but if the pump
has a positive motion, the delivery valve must open wide enough to let
the water out, or pressure enough may be got up in the pump to break it.
A check valve is merely a second delivery valve placed close to the
boiler and serving to enable the pump to be taken apart if occasion
should arise, without letting the water out of the boiler.
The lift and fall of both valves act to impair the capacity of the pump.
Thus, while the suction valve is falling to its seat, the water already
in the pump passes back into the suction pipe, and similarly, while the
delivery valve is closing, the delivery water passes back.
A foot valve is virtually a second suction valve placed at the bottom or
foot of the suction pipe.
The capacity of a pump is from 70 to 85 per cent. of the displacement of
the plunger or piston, and varies with the speed at which the plunger or
piston runs.
If a pump runs too fast, the water has not sufficient time to follow the
piston or plunger, especially if the suction pipe has bends in it, as
these bends increase the friction of the water against the bore of the
pipe.
The speed of the piston or plunger should not exceed such as will
require the water to pass through the suction pipe at a speed not
greater than 500 feet per minute, and better results will be obtained at
350 feet per minute.
An air chamber placed above the suction pipe of any pump causes a better
supply of water to the pump by holding a body of water close to it, and
by making the supply of water up the suction pipe more uniform and
continuous. Air chambers should be made as long in the neck as
convenient, so that the water in passing through the pump barrel to the
delivery pipe could not be forced up into the chamber, as, if such be
the case, the air in the chamber is soon absorbed by the water.
Belt pumps are more economical than independent steam pumps, because the
power they utilize is more nearly the equivalent of the power it takes
to drive them, whereas in steam pumps there is a certain amount of
steam, and therefore of power, expended in tripping the valves and in
filling the clearance spaces in the cylinder. Furthermore, the main
engine uses the steam expansively, whereas the steam pump does not.
[Illustration: _VOL. II._ =AMERICAN FREIGHT LOCOMOTIVE.= _PLATE XXIX._
Fig. 3326.]
CHAPTER XXXVIII.--THE LOCOMOTIVE.
In Fig. 3326 is shown a modern freight locomotive, the construction
being as follows:
For generating the steam we have the boiler, which at the front end is
firmly bolted to the engine cylinders, which are in turn bolted to the
frames, while at the back end the boiler is suspended by the links B
(one at each end of the fire box on each side of the engine).
The starting bar is shown in position to start the engine, and it is
seen that the rod _a_ and bell crank _b_ are in such a position as to
open the valve T, and thus admit steam from the dome to the pipe _e_,
whence it passes through pipes _f_, _g_ and _r_ into the steam chest
_i_, the slide valve V distributing the steam to the cylinder. The
exhaust occurs through the exhaust port _d_, whence it passes up the
exhaust pipe and out at the smoke stack.
The boiler is fed with water as follows:
The _feed pipe from the tender_ supplies water to the injector, which is
forced by the injector through the _feed pipe to boiler_ and into the
latter.
In the figure the parts are shown in position for the engine to go
ahead, hence the reversing gear is in the extreme forward notch of the
sector, and the valve gear is in full gear for the forward motion.
The lever _m_ is for opening and closing the cylinder cocks, which are
necessary to let the water of condensation out of the cylinder when the
engine is first started and the cold cylinder condenses the steam.
To supply steam to the injectors (of which there are two, one on each
side of the engine) and to the steam cylinder of the pump, there is a
steam pipe leading from the dome to the steam drum, the pipe K supplying
steam to the injector, and pipe J supplying steam to the steam cylinder
of the air pump. The pipe for supplying oil to the slide valve and
cylinder is furnished with a sight feed oil cup, the oil being carried
by steam from the steam drum.
This pipe passes beneath the lagging until it reaches the smoke box,
which is done to keep it warm and prevent the oil from freezing, while
the steam pressure enables the oil to feed against the steam pressure in
the steam chest.
The slide valve is balanced by means of strips let into its back, and
bearing against a plate fixed to the steam chest cover.
The frame on the side of the engine shown in the engraving is shown
broken away from the yoke A to the fire box, so as to expose the link
motion to full view, the shaded portion of the frame being that on the
other side of the engine.
The yoke or brace A carries one end of the guide bars. The safety valve
S may be raised to see that it is in working order, or to regulate the
steam pressure, by the lever O, which has a ratchet tongue engaging with
the notches at _l_.
[Illustration: Fig. 3326_a_.]
[Illustration: Fig. 3326_b_.]
In addition to the safety valve with spring balance, however, a pop
safety valve is employed on the part of the dome that is shown broken
away, the construction of this pop valve being shown in the outside
view, Fig. 3326_a_, and a sectional view, Fig. 3326_b_, the casing being
removed from the latter. In the valve seat B is a recess _a_, and upon
the circumference of the valve is a threaded ring C´. When the valve
lifts, the steam is somewhat confined in the annular recess of the
valve, and the extra valve area thus receiving pressure causes the valve
to lift promptly and the steam to escape freely. The degree of this
action is governed as follows:
The sleeve C´ is threaded upon the upper part of the valve, so that by
screwing it up or down upon the valve the amount of opening between the
annular recess _a_ _a_, and the lower edge of the sleeve C´ C´, is
increased or diminished at will; the less this opening, the more
promptly the valve will rise after lifting from its seat.
To secure the sleeve or ring in its adjusted position, the ends of the
screws L, L seat in notches cut in the upper edge of the sleeve. In many
engines pop valves alone are used, and in some cases levers are provided
by means of which the pop valve can be raised from its seat to test if
it is in working order.
Referring again to Fig. 3326, H is the handle for operating the
injector, and _w_ a rod for opening the injector overflow.
We now come to the automatic air brake; steam for the steam cylinder of
which, is received from the steam drum through the pipe J, passing
through the pump governor, or regulator G. The exhaust pipe for the
steam cylinder of the air pump passes into the smoke box. The air
cylinder receives its supply of air through the small holes at _k_, _k_,
and delivers it through the pipe C into the air reservoir or tank, from
which it passes through the tank pipe up to the threeway cock or
engineer's brake valve, whose handle is shown at M. The brakes are kept
free from the wheels and out of action so long as there is air pressure
in the air reservoir and in the train pipe, hence the normal position of
the handle M is such as to let the air pass from the air reservoir up
the pipe _x_ and into the train pipe. When the brakes are to be applied,
handle M is moved so that there is an open connection made between the
train pipe and the _pipe to open_ air, which releases the air pressure
and then puts on the brakes not only on each car, but also on the
engine, because the engine brake cylinders receive their air pressure
from the pipe shown leading to the train pipe. From the tank pipe _x_ a
pipe _h_ leads to the top of the pump governor G, whose action is to
shut off the steam from the steam cylinder of the air pump whenever the
pressure in the air reservoir or tank exceeds 70 lbs. per square inch. A
small pipe leads up from pipe _h_ to the air pressure gauge.
For regulating the draught of the fire there is a damper door at each
end of the ash pan, and to increase the draught, a pipe leads from the
steam drum into the smoke box, where it passes up alongside of the
exhaust pipe, its end being shown at Z. This is called the _blower_, and
its pipe is on the other side of the engine. The plate shown at P, P in
the smoke box checks the draught in the upper tubes, and therefore
distributes it more through the lower ones.
[Illustration: Fig. 3327.]
There are two sand valves, both of which are operated by one rod, the
construction being shown in Fig. 3327, which is a plan showing the
bottom of the sand box broken away to expose the gear for moving the
valves. The two valves _v_, _v_ for the sand pipes are on raised seats
_e_, _e_, and are fast on the same shafts as the segments _s_, _s_, but
the valves are obviously above, while the segments are beneath the
bottom of the sand box. The gear wheel W is pivoted to the under side of
the bottom of the sand box, and the arm L is fixed to the wheel. At _t_
are pieces of wire, which, being fast in the spindle, revolve with it
and stir up the sand when the valves are moved. As shown in the figure,
the two sand pipes _a_, _a_ are open, but suppose the rod is moved
endways and L will revolve W, which will move _s_, _s_ and the valves
_v_, _v_, causing the latter to move over and cover the pipes _a_, _a_,
and shut off the sand from the pipes.
Fig. 3328 represents an American passenger locomotive with a steam
reversing gear, or in other words, a reversing gear that is operated by
steam.
The link motion is substantially the same as that shown in Fig. 3326 for
a freight locomotive, the eccentric rods in this case being straight, as
there is no wheel axle in the way.
The injector for feeding the boiler is the same as that shown on the
freight locomotive.
The ash pan is provided with two dampers, one at each end, and the front
one is operated by the bell crank _a_ _c_.
The sand boxes are here fastened to the frame, both sand valves being
operated by the lever _m_, which at its lower end connects to a rod,
_u_, which at its back end connects to an arm, _p_, on a shaft that
extends across the fire box and connects to a rod corresponding to rod
_u_, but situated on the other side of the engine and connecting with
the other sand valve.
The steam pump for the automatic air brake is on the other side of the
engine, and the air reservoirs, of which there are two, are horizontal
and situated beneath the front end of the boiler. The air pipe to the
triple valve here connects to the front pipe of the three beneath the
triple valve, the middle pipe being that which is open to the
atmosphere, which is the usual construction. The engine brake receives
its air from a pipe on the other side of the engine which feeds the
pipes G, V, for the brake cylinder shown in the figure. When the engine
is running backwards, the train brakes are operated through the medium
of the "pipe to air brake and to front end of engine" which is shown
broken off.
The construction of the steam reversing gear is shown in Fig. 3328_a_. A
is a steam cylinder and B a cylinder filled with oil or other liquid.
Each of these cylinders has a piston, the two being connected together
by their piston-rods C C´. These rods are also connected to a lever D E
F, which works on a fulcrum E. The lower end of the lever is connected
to the reverse rod F G, the front end of which is attached to the
vertical arm of the lifting or reverse shaft. It will readily be seen
that if the piston in B is free to move and steam is then admitted to
either end of the steam cylinder A, the two pistons will be moved in a
corresponding direction, and with them the lever D E F, and the other
parts of the reversing gear. A valve, H, is provided, by which
communication is opened between the cylinder A and the steam inlet pipe.
Another valve, I, is placed between H and the cylinder A, by which the
steam may be admitted either into the front or back end of the cylinder.
It will be apparent, though, that if the piston in A is thus moved, and
the reverse gear placed in any required position, some provision must be
made to hold it there securely. This is accomplished by the oil cylinder
and piston B. To it a valve, J, is provided, by which communication
between the front and back ends of the cylinder may be opened or closed.
It is evident that if the piston B is in any given position, and both
ends of the cylinder are filled with liquid, the former will be held
securely in that position if the liquid in one end cannot flow into the
other. If, however, communication is opened between the two ends, then,
if a pressure is exerted on the piston B, it will cause the liquid to
flow from one end of the cylinder to the other, and thus permit B to
move in whichever direction the pressure is exerted.
[Illustration: _VOL. II._ =AMERICAN PASSENGER LOCOMOTIVE.= _PLATE XXX._
Fig. 3328.]
[Illustration: Fig. 3328_a_.]
R is the reverse lever, made in the form of a bell crank, the short end
of which works in a slot _c_, in the upper end of a shaft or spindle
_d_. This shaft is inclosed by a tubular shaft S, to which the fulcrum
of R is fastened. The tubular shaft has an arm _b_. The reverse lever
has two movements, the one to raise the end up, and the other to turn on
the axis of the tubular shaft. The arm _b_ on the latter is connected by
a rod, _f_, with the valves J and H. The lower end of the shaft _d_ is
connected with a bell crank, _f´_, which, in turn, is connected by a
rod, _k_ _l_, with the valve I. Therefore, by turning the lever R so as
to partly revolve the shaft S, the valves J and H may be opened or
closed, and by moving the lever R up or down, the valve I is moved to
admit steam to the front or back end of A. To reverse the engine,
therefore, the lever R is turned so as to open the valves J and H. This
opens communication between the opposite ends of B, and H admits steam
to I. Now, by reversing the end of the reverse lever R, the valve I is
moved so as to admit steam to either end of A, the pressure in which
will move the reverse gear to the desired position. When this is done,
the valves J and H are closed. This prevents the fluid in B from flowing
from one end of the cylinder to the other, and thus securely locks the
piston B in the position it may happen to be in, and at the same time
the valve H shuts off steam from the cylinder A.
The bar K is graduated, as shown in the plan of R, K, to indicate to the
locomotive runner the position of the reversing gear.
This apparatus enables the reversing gear to be handled with the utmost
facility, and with almost no exertion on the part of the engineer. The
engine can be reversed almost instantly, and it can be graduated with
the most minute precision.
THE LINK MOTION AND REVERSING GEAR.
The link motion of an American locomotive is shown in Figs. 3329 and
3330. In Fig. 3329 it is shown in full gear for the forward gear, or in
other words, so as to place the engine in full power for going ahead.
The meaning of the term full power is that, with the link motion in full
gear, the steam follows the piston throughout very nearly the full
stroke.
[Illustration: Fig. 3331.]
[Illustration: Fig. 3332.]
In Fig. 3331 the link motion is shown in mid gear, in which position the
engine is at its least power, the cut off occurring at its earliest
point, and in Fig. 3332 it is shown in full gear for the backward
motion.
[Illustration: _VOL. II._ =LOCOMOTIVE LINK MOTION.= _PLATE XXXI._
Fig. 3329.
Fig. 3330.]
Referring to Fig. 3329 for the full gear forward, the reversing gear
proper consists of the reversing lever, the segment, the reach rod, the
tumbling shaft, and its counterbalance rod and spring; while the link
motion proper consists of the eccentrics and their rods, the link, the
link block or die, the suspension link S, the rock shaft and the rod P
P. These, however, are terms applied for shop purposes, so as to
distribute the work in sections to different men, it being obvious that
a _complete_ link motion includes the reversing gear, the eccentrics,
the link and its block, the rock shaft, the rod P P, and the valve and
its spindle or stem. This mechanism, as a whole, may also be called, and
is sometimes called, the valve gear, because it is the mechanism or gear
that operates the slide valve.
The link motion may be moved from full gear forward to full gear
backward or to any intermediate position, whether the engine is running
or at rest, but is, when the engine is running, harder to move from full
gear forward toward back gear, and easier to move from full gear
backward toward mid and forward gears, which occurs because of the
friction of the eccentrics in the straps, and it follows that this will
be the case to a greater extent in proportion as the revolutions of the
eccentrics are increased.
If in a properly constructed link motion we move the link from full gear
forward to mid gear when the engine is standing still, and watch the
valve, we shall find that the lead or opening at _f_ gradually
increases; and if we then move it from mid gear to full gear backward,
the lead will gradually decrease and finally become the same as it was
in full gear forward. The construction of the parts is as follows:
Referring to Fig. 3329 (full gear forward), the segment is fixed in
position and the reversing lever is pivoted at its lower end. _r_ _r_ is
a bell crank, which is pivoted to the reversing lever and to which the
latch rod is pivoted at its upper end. The spring acts on the end of _r_
_r_, and thus forces the tongue of the latch into the notches on the
sector as soon as the tongue comes fair with the notch and _r_ _r_ is
released from the hand pressure. As the reversing lever is moved over
from full gear forward, the reach rod moves the tumbling shaft, whose
lower arm _i_ (through the medium of the suspension link S) lifts the
link and brings the centre of the saddle pin nearer to the centre of the
pin in the link block, which reduces the amount of motion given to the
lower arm (B, Fig. 3331) of the rock shaft, and therefore reduces the
amount of valve travel, thus causing the point of cut-off to occur
earlier in the piston stroke.
The weight of the eccentric rods, the link, suspension link S, and the
tumbling shaft arm _i_, is counterbalanced by the counterbalance spring
in the box _s_ _s_, whose rod attaches to the lug _g_ on the tumbling
shaft. To regulate the proper amount of counterbalancing, the nuts at
_m_ are provided, these nuts regulating the amount of tension on the
spring _s_ _s_.
The forward eccentric E is that which operates the valve when the link
motion is in full gear forward, as in Fig. 3329, and the backward
eccentric is that which moves the valve when the link motion is in back
gear, as in Fig. 3332.
This occurs because it is the eccentric rod that is in line or nearest
in line with the link block that has the most effect in moving the
valve. When the link is in full gear, the motion of the valve is almost
the same as though there was no link motion and the eccentric rod was
attached direct to the rod P P, the difference being so slight as to
have no practical importance. This will be seen by supposing that we
were to loosen the backward eccentric F upon the shaft and revolve it
around the shaft by hand, in which case it would swing the lower end of
the link backward and forward with the centre of the link block as a
pivot or centre of motion, the forward eccentric rod rising and falling
a trifle only, and therefore moving the rock shaft to a very slight
amount.
Let it now be noted that the suspension link not only sustains the
weight of the link and eccentric rods, but also compels the centre of
the saddle pin to swing (as the link is moved by the eccentrics) in an
arc of a circle of which the centre is the upper end of the suspension
link. Suppose, therefore, that the backward eccentric rod was to break,
or was taken off and the engine could still run forward, but no motion
would be given to the valve, if the link was placed in mid gear, because
in that case the forward eccentric rod would simply swing the link on
the centre of the link block as a pivot. Now, suppose the forward
eccentric rod was to break or be taken off, and the engine may be made
to go ahead by setting the backward eccentric fair with the forward
eccentric and connecting its rod to the upper end of the link.
Similarly, if the engine was running with the smoke stack toward the
train and the link motion in backward gear, and the backward eccentric
rod was to break, we may take it off, shift the forward eccentric so
that it comes fair or stands in line with the backward eccentric and
connect its rod to the lower end of the eccentric and with the link
motion in backward gear, the engine would still haul the train.
If the reach rod was to break, the tumbling shaft could be held in
position by loosening the cap bolts of the tumbling shaft journal and
putting between the cap and the tumbling shaft journal a piece of metal,
which, on bolting up the cap screws again, would firmly grip the shaft
and prevent it from moving.
[Illustration: Fig. 3333.]
SETTING THE SLIDE VALVES OF A LOCOMOTIVE.--The principles of designing,
and the action of D valves, such as are used upon locomotives, have been
so thoroughly explained with reference to stationary engines, that there
is no need to repeat them in connection with the locomotive, and we may
proceed to explain how to set the valves of a locomotive. In doing this,
there are two distinct operations, one of which is to place the crank
alternately exactly on its respective dead centres, and the other is to
set the position of the eccentrics, and get the eccentric rod of the
proper length. These two operations comprise all that require to be done
to set the valves, under ordinary and workmanlike conditions; hence we
may proceed at once to explain the operation.
The first thing to be done is to put the crank pin on a dead centre, and
it does not matter which one.
In Fig. 3333 it is supposed that the piston is to be at the head end of
the cylinder when the crank is on its corresponding dead centre.
The first thing to do is to put the reversing gear in full gear forward,
so as to set the forward eccentric, and see if its rod is of proper
length.
The next thing to do is to move the wheel so that the crank pin is
nearly on the dead centre, and then take a tram (such as shown in the
figure), pointed at each end, and mark on the splash plate, or any other
convenient place, a centre punch dot in which the point _b_ of the tram
can rest. Next, from the centre of the axle as a centre, mark arcs or
portions of circles _a_, _a_. This being done, point _b_ of the tram is
rested in the centre punch dot before referred to, and with the other
end a line _c_ is marked, a straight edge is then rested against the
ends _e_ _e_ of the cross head, and a line _d_ is marked on the guide
bar, this line being exactly even or fair with the end _e_ _e_ of the
cross head.
We then move the wheel in the direction of the arrow, and as soon as we
begin to do so, the cross head will move to the left and away from the
line _d_ on the guide bar. But as soon as the crank pin has passed its
dead centre, the cross head will begin to move to the right, and as soon
as the end _e_ _e_ comes again exactly in line with the line _d_ marked
on the guide bar, we must stop moving the wheel, and again resting the
point _b_ of the tram in the centre punch mark before mentioned, we move
its other end so as to mark a second line, which will be the line or arc
_f_.
The next thing to do is to mark a fine centre punch dot, where _c_ and
_f_ cross the arc or line _a_, and then find the point _g_ midway
between _f_ and _c_, and mark a fine centre punch mark there. This being
done, we must move the wheel back into the position it occupies in the
figure, and then slowly move it in the direction of the arrow, until
with the end _b_ of the tram resting in the centre punch dot, the other
end of the tram will fall dead into the centre punch dot at _g_, at
which time the crank pin will be exactly on the dead centre.
During this part of the process we have nothing to do with anything
except getting the crank pin on the dead centre, but there is one point
that requires further explanation, as follows:
In this operation we have first put the crank on one side of the dead
centre and then put it to the same amount on the other side of the dead
centre, both being improper positions; but by finding the mean or mid
position between the two, we have found the proper position. In doing
so, however, we have moved the wheel, the wheel has moved the connecting
rod, and the connecting rod has moved the piston. But in the actual
running of the engine, this order of things will be reversed; for the
steam will move the piston, the piston will move the connecting rod, and
the connecting rod will move the crank and therefore the wheel.
The difference between the two operations is this: Suppose there is lost
motion or play between the connecting rod brasses and the crank pin, or
between the connecting rod brasses and the cross head pin, and then if
we move the wheel in the direction denoted by the arrow, we take up this
lost motion, so that if the tram was fair with the centre punch at _g_
and steam was admitted to the piston, then there would be no lost motion
to take up, and as soon as the piston moved the crank pin would move.
But if we moved the wheel in the opposite direction to that denoted by
the arrow, then we are placing any lost motion there may be in the
opposite direction, and if steam were turned on, the piston and
connecting rod might move before the crank and wheel moved.
In which direction the wheel should be moved while placing the crank on
the dead centre depends upon the condition of the engine, as will be
explained presently, the assumption being at present that the engine is
in thorough good order, in which case the wheel should (while placing
the crank on the dead centre) be moved in the direction of the arrow in
the figure.
The object is under all conditions to bring the working surfaces to bear
(while setting the valve) in the same way as they will bear when the
engine is actually at work.
Having placed the crank on the dead centre, and thus completed the first
operation in valve setting, we may turn our attention to the second,
viz., correcting the lengths of the eccentric rods and setting the valve
lead. Almost all writers who have dealt with this part of the subject
have fallen into a very serious error, inasmuch as they began the
operation by what they call _squaring_ the valve. This means so
adjusting the length of the eccentric rod that the valve will travel an
equal distance each way from its mid position, so that if the engine
wheel is revolved and the extreme positions of the valve marked by a
line, these lines will measure equally from the edges of the steam
ports, or, what is the same thing, from the centre of the cylinder
exhaust port. This procedure is entirely erroneous, because, on account
of the angularity[57] of the eccentric rod, the valve cannot, if equal
lead is to be given to the valve, travel equally beyond the two steam
ports, and if the eccentric rods are so adjusted for length as to
_square the valve_, they are made wrong.
[57] See page 376, Vol. II., for the meaning of angularity.
The valve lead, and the lead only, it is that determines the length of
the eccentric rods. Suppose that, as is generally the case, the lead is
to be equal, or, in other words, that there is to be as much valve lead
when the piston is at one end of the cylinder as there is when it is at
the other, and if we make the eccentric rods of such a length that the
valve travels equally on each side of the steam port, there will be less
lead at the head end port than there is at the crank end port. The
proper method, therefore, is (as soon as the crank is on the dead centre
and the link in full gear, as in Fig. 3334) to set the eccentric so as
to give the desired amount of lead, and then give the wheel a half
revolution, the lower end of the tram falling into the centre punch dot
at _s_, when the crank pin will be on its other dead centre and ready
for the lead to be measured again. If the lead is equal at each end, one
eccentric rod is of the right length, and all we have to do is to set
the eccentric so that the right amount of lead is given.
We now turn our attention to the backward eccentric and its rod, putting
the reversing lever in full gear for the backward motion, and putting
the crank on the respective dead centres, and testing the lead for both
ports as before, and when the required amount of valve lead is given the
valve setting is complete.
In some practice the wheel is blocked up on the pedestal guides while
setting the valves, but a more correct method is to let the engine rest
on the rails and push it back and forth with a crowbar to revolve the
wheels when putting the crank pin on the dead centre. The best thing to
measure the lead with is a wooden or leaden wedge having but a slight
degree of taper, as say 3/16 or 1/4 inch in a length of four inches. We
have in this example of valve setting supposed the parts to be of the
proper dimensions, as they would be in a new engine or in an engine that
had been running and merely had a new valve or a new eccentric put in.
But suppose the notches were not cut in the sector, and we have then to
mark them off while setting the valves. All the difference that this
makes to the operation is that we must clamp the reversing lever to the
sector while setting the valve, taking care to so clamp it that there is
the same space between the top end of the link block and the end of the
link slot in the full forward gear as there is between the bottom end of
the link block and the end of the link slot when the engine is in full
backward gear. In this connection it is, however, to be remarked that
when the link is in full gear, either forward or backward, and the crank
is on the dead centre, the link block is not at the end of its motion
toward the end of the link slot; hence it is a good plan to move the
wheels around and to so regulate the length of the reach rod and the
position of the reversing lever on the sector, that when the link block
is at the highest point in the link slot for the forward gear and at the
lowest point in the link slot for the backward gear, it comes an equal
distance from the end of the link slot.
[Illustration: _VOL. II._ =INJECTOR AS APPLIED TO A LOCOMOTIVE.= _PLATE
XXXII._
Fig. 3337.
Fig. 3338.]
[Illustration: Fig. 3334.]
The setting for an Allen valve is the same as that for an ordinary one,
but in determining the amount of the lead it is to be borne in mind that
it is virtually twice as much as it measures at the port because there
are two openings for the steam. This will be seen from Fig. 3335, in
which the valve is open to the amount of the lead at _f_. But the steam
also enters at _e_, and passes through the port in the valve and into
steam port _a_.
We have now to call attention to the fact, that the eccentric rods, when
properly connected, are, in an American locomotive, crossed when the
piston is at the crank end of the cylinder. In Fig. 3334, the piston is
at the head end of the cylinder, and the rods are open. In Fig. 3336,
however, the crank pin is supposed to be at B, and the eccentric rods
are crossed, F being the forward and E the backward eccentric.
THE INJECTOR.
The injector shown in the general view of a freight locomotive, Fig.
3326, is that constructed by William Sellers & Co., and there are two,
one on each side of the engine. The details of its construction are as
follows:
Fig. 3337 is a side elevation, Fig. 3338 a section on a vertical plane,
Fig. 3339 a section on a horizontal plane, Fig. 3340 an end view of the
injector at the right-hand side of the engine, and Fig. 3341 a plan of
the injector on the left-hand side of the engine.
This injector is self-contained, or in other words, it has both steam
and check valves, so that it can be connected directly without other
fittings, although, of course, it is generally desirable to place
another stop valve in the steam pipe, and a check valve in the delivery
pipe, so that the injector can be taken to pieces or disconnected at any
time. Another important feature of this injector is, that it is operated
by a single handle, and that the waste valve is only open at the instant
of starting.
Referring to Fig. 3338, A is the receiving tube, which can be closed to
the admission of steam by the valve X. A hollow spindle passing through
the receiving tube into the combining tube is secured to the rod B, and
the valve X is fitted to this spindle in such a way that the latter can
be moved a slight distance (until the stop shown in the figure engages
with valve X) without raising the valve X from its seat. A second valve
W, secured to the rod B, has its seat in the upper side of the valve X,
so that it can be opened (thus admitting the steam to the centre of the
spindle) without raising the valve X from its seat, if the rod B is not
drawn out any farther, after the stop on the hollow spindle comes in
contact with the valve X. D is the delivery tube, O an overflow opening
into space C, V the check valve in delivery pipe, and Z the waste valve.
The upper end of the combining tube has a piston N N attached to it,
capable of moving freely in a cylindrical portion of the shell M, M, and
the lower end of the combining tube slides in a cylindrical guide formed
in the upper end of the delivery tube.
The rod B is connected to a cross head which is fitted over the guide
rod J, and a lever H is secured to the cross head. A rod W, attached to
a lever on the top end of the screw waste valve, passes through an eye
that is secured to the lever H; and stops T, Q control the motion of
this rod, so that the waste valve is closed when the lever H has its
extreme outward throw, and is opened when the lever is thrown in so as
to close the steam valve X, while the lever can be moved between the
positions of the stops T, Q without affecting the waste valve. A latch F
is thrown into action with teeth cut in the upper side of the guide rod
J, when the lever H is drawn out to its full extent and then moved back;
and this click is raised out of action as soon as it has been moved in
far enough to pass the last tooth on the rod J. An air vessel is
arranged in the body of the instrument, as shown in the figure, for the
purpose of securing a continuous jet when the injector and its
connection are exposed to shocks, especially such as occur in the use of
the instrument on locomotives.
[Illustration: Fig. 3335.]
[Illustration: Fig. 3336.]
The manipulation required to start the injector is exceedingly
simple--much more so in practice, indeed, than it can be rendered in
description. Moving the lever H until contact takes place between valve
X and stop on hollow spindle, which can be felt by the hand upon the
lever, steam is admitted to the centre of the spindle, and, expanding as
it passes into the delivery tube D and waste orifice P, lifts the water
through the supply pipe into the combining tube around the hollow
spindle, acting after the manner of an ejector or steam siphon. As soon
as solid water issues through the waste orifice P, the handle H may be
drawn out to its full extent, opening the steam valve X and closing the
waste valve, when the action of the injector will be continuous as long
as steam and water are supplied to it.
To regulate the amount of water delivered, it is necessary only to
move in the lever H until the click engages any of the teeth on the
rod J, thus diminishing the steam supply, as the water supply is
self-regulating. If too much water is delivered, some of it will escape
through O into C, and, pressing on the piston N N, will move the
combining tube away from the delivery tube, thus throttling the water
supply; and, if sufficient water is not admitted, a partial vacuum will
be formed in C, and the unbalanced pressure on the upper side of the
piston N N will move the combining tube toward the delivery tube, thus
enlarging the orifice for the admission of water. From this it is
evident that the injector, once started, will continue to work without
any further adjustment, delivering all its water to the boiler, the
waste valve being kept shut. By placing the hand on the starting lever,
it is easy to tell whether or not the injector is working; and, if
desired, the waste valve can be opened momentarily by pushing the rod W,
a knob on the end being provided for the purpose.
[Illustration: Fig. 3339.]
[Illustration: Fig. 3340.]
[Illustration: Fig. 3341.]
THE WESTINGHOUSE AUTOMATIC AIR BRAKE.
Figs. 3342, 3343 and 3344 represent the Westinghouse automatic air brake
applied to an engine and tender, and in the following figures details of
the construction of various parts are shown.
[Illustration: Fig. 3345.]
The pump governor, which is shown at G in Fig. 3326, of a modern freight
locomotive, is shown in section in Fig. 3345.
The pump governor is employed for the purpose of cutting off the supply
of steam to the pump when the air pressure in the train pipe exceeds a
certain limit, say 70 lbs. per square inch.
Its operation is as follows:
When valve 10 is (by means of hand wheel 8) screwed home to its seat the
steam is entirely shut off from the steam cylinder, but by operating
wheel 8 to unscrew spindle 9, valve 10 is permitted to open and let the
steam pass through A and B to the steam cylinder which operates, forcing
air into the reservoir and thence into the train pipe. A pipe from the
train pipe connects to the upper end of the pump governor, hence air
from the train pipe passes around the stem 14 to the upper side of the
thin diaphragm 18, which is held in its position by the spring 12 with a
force sufficient to enable it to resist, without moving, a pressure of
70 lbs. per square inch. But when the pressure exceeds 70 lbs. per
square inch it forces the diaphragm down, pushing down valve 13 and
allowing the steam in A to pass up through valve 13 and out of the
exhaust pipe 6. The steam pressure in A being thus reduced, that in B
acts on the under side of the valve, causing it to rise and seat itself
and thus cut off the supply of steam to the pump.
[Illustration: _VOL. II._ =LOCOMOTIVE AIR BRAKES.= _PLATE XXXIII._
Fig. 3342.
Fig. 3343.
Fig. 3344.]
When the pressure in the train pipe is diminished by the brakes being
applied, the diaphragm is restored to the position it occupies in the
figure by the action of the spring 16. Then valve 13 is seated by the
spring 12, and the steam pressure accumulates on the upper end of valve
10, forcing it down and letting the steam from A into B and thence into
the steam cylinder, starting it into action, which continues until the
pressure in the train pipe exceeds 70 lbs. per square inch.
The use of this governor not only prevents the carrying of an excessive
air pressure in the train pipe, which may result in entirely preventing
the wheels from revolving and causing a flat place to wear on the wheel
tire, but it also causes the accumulation of a surplus of air pressure
in the main reservoir, while the brakes are applied, which insures the
release of the brakes without delay. It also obviates the unnecessary
working of the pump when the desired air pressure has been obtained.
[Illustration: Fig. 3346.]
A sectional view of the steam and air cylinders is shown in Fig. 3346,
the construction being as follows:
Steam is distributed to the steam cylinder by means of a piston valve,
composed of three pistons, marked 16, 14, and 20 respectively, the steam
entering between pistons 16 and 14, and, in the positions in which the
parts occupy in the figure, steam can pass through the bushing 18 and
beneath the steam piston 7, propelling it upwards until the bottom of
the hole in its piston rod strikes the end of rod 12, and raises it and
valve 13. The chamber 23, in which valve 13 works, receives steam
through a suitable port from the steam space between valves 14 and 16;
and the steam from chamber 23, it is that (in the positions the parts
occupy in the figure), acting on the area of the large valve piston 20,
holds the valve down against the pressure on the bottom face of piston
14 of the valve. As soon, however, as the piston rod 7 strikes and
raises rod 12 and valve 13, the steam is exhausted from the top of
piston 20 of the valve, and the steam beneath piston 14 of the valve
raises the valve, opening the lower port in the sleeve 18 for the
exhaust, and piston 14 admits steam to the upper side of the steam
piston 7. The construction of the air cylinder differs somewhat from
that shown in the freight locomotive, Fig. 3326, this air pump
corresponding with that shown on the engine and tender, Fig. 3342. A
detail list of the parts may be given as follows:
No.
2. Steam cylinder head (with reversing cylinder, piston, and valve
bushes).
3. Steam cylinder (with main valve and bushes).
4. Centre piece.
5. Air cylinder (with lower discharge valve).
6. Air cylinder head.
7. Steam piston and rod.
8. Air piston.
9. Piston rings.
10. Steam piston plate.
11. Steam piston bolt.
12. Reversing rod.
13. Reversing valve.
14. Piston valve.
15. Piston valve rings.
16. Piston valve rings.
17. Upper valve bushing.
18. Lower valve bushing.
19. Reversing piston casing.
20. Reversing piston.
21. Piston rings.
22. Reversing cylinder cap.
23. Reversing valve bush.
24. Reversing valve cap.
25. Piston rod nut.
26. Piston packing gland.
27. Piston packing nuts.
28. Packing glands.
29. Right Chamber cap.
30. Left chamber cap.
31. Air valve bushing.
32. Air valve.
33. Air valve.
34. Air valve.
35. Delivery union.
36. Exhaust steam outlet.
40. Steam cylinder gasket.
42. Top air-pump gasket.
43. Bottom air-pump gasket.
44. Waste water pipe.
46. Exhaust union stud.
49. Air exhaust union stud.
A side view of the driving wheel brakes is shown in Fig. 3347 and an end
view in Fig. 3348. The brakes are, it is seen, suspended by links so
that their weight tends to keep them from the wheels. The brake piston
rod carries at its end two links which attach to the arms attached to
the brakes. The ends of these arms being curved roll together, the
arrangement forming in effect a rolling toggle joint. The construction
of the piston of the driving wheel brake is shown in Fig. 3349. The
piston is made air tight by leather packing indicated by 11, held out by
a spring 12. The piston rod packing, 7, is leather held in place by the
cap 6 and the spring 8. The air for operating the brake enters below the
piston.
[Illustration: Fig. 3347.]
[Illustration: Fig. 3348.]
LOCOMOTIVE RUNNING.
The engineer's duty in running a locomotive is more arduous and requires
more watchfulness than any other engine running, because of the
peculiarities attending it. In the first place, the jolts and jars to
which the engine is subject are liable to cause nuts, pins, etc., to
come loose, and some of the parts to become disconnected and cause a
breakdown of the engine.
This renders necessary a careful examination of the engine, which should
be made both before and after each trip.
In the second place, we have that the amount of load the engine has to
pull varies with every varying grade in the railroad track, and the
variation is so great that on some descending grades the engine may
require no steam whatever, while on ascending grades the utmost power
attainable from the engine may be required. In firing, feeding the
pumps, oiling the parts, and determining the depth of water in the
boiler, the grade and the length of each grade has an important bearing,
and so has the weather, since it is clear that between the heat of
summer and the blizzards of winter there is a wide range of the
conditions under which the engine runs.
In former times, from the less perfect construction of locomotives, the
engineer's duties were greatly enhanced from breakdowns, which are
comparatively rare with modern locomotives, and there is promise that
from improved construction and safeguards they will become less frequent
in the future.
It is as important for the locomotive engineer to be familiar with the
track as it is to be with the engine, and there is no field of engine
driving or running in which more scope is permitted to the engineer to
exercise judgment and skill in his management, so as to effect economy
in fuel consumption.
The quality and size of the coal is another element that requires
attention and observation on the part of the engineer, in order that his
train may keep its time and the fuel consumption be kept down.
GETTING THE ENGINE READY.
The first thing to be done in getting ready for a trip is to see that
there is sufficient water in the boiler, so that if there is not, there
is time to supply the deficiency.
If the boiler is cold it may be that the condensation of the steam in
cooling may have left a partial vacuum in the boiler, and it will be
necessary in that case to open the top gauge cock and let in air so that
the water will come to its proper level in the gauge glass. Similarly,
in filling the boiler, it may be necessary to open a gauge cock to let
the air out.
The lower cock of the gauge glass should be opened to let the steam blow
through if there is pressure on the boiler, or to let a little water out
if there is not.
The safety valve should next be examined and moved to see that it works
properly and does not stick to its seat.
Before laying the fire the fire bars and ash pan should be cleared of
ashes and clinkers, and the grate bars tried with the shaking levers to
see that the grates will shake properly. It should be seen that the
tubes, etc., are clear of ashes.
In laying a new fire an ample supply of lighting material should be
used, disposing it so that the fire will light evenly and not in spots,
and a good layer of wood should be evenly distributed over the bars, the
thinnest pieces being at the bottom as they will light easiest, and it
is necessary to light the fire at the bottom, so that the heat from the
wood that is first lighted shall pass through that to be lighted.
The wood should be kept burning without coal until the lower stratum
has ceased to blaze and covers the bars, while there is an even layer of
blazing wood above it.
[Illustration: Fig. 3349.]
The quantity of coal to be fed at a time, and the depth of fire to be
kept, depends upon the size of the coal, because the larger the coal the
less it obstructs the draught, and the thicker the layer required in
order to prevent currents of air from passing through without entering
into combination with the gases from the coal.
If the coal is mixed, containing large lumps, they should be broken.
The first layer of coal should be enough to cover the fire to a depth of
about two inches, which will permit of a good draught. This will get
well alight while the wood is still serviceable, and a second layer may
be applied of another two inches. The third feeding should be given with
a view to have a greater depth of fire at the sides than at the middle
of the fire box, because the cool sides of the box prevent perfect
combustion, and currents of cold air are more apt to find their way
through the sides than in the middle of the fire box.
Banking a fire consists of piling it up at the back half of the fire box
and covering it up with green coal, so that it may keep alight and keep
the boiler hot without increasing the steam pressure.
The air passing through the uncovered half of the fire bars prevents
rapid combustion and a dead fire is maintained.
In starting up a banked fire, the first thing to do is to clean it of
ashes, clinker, etc., shaking up the bars to see that they will work
properly. The fire is then spread evenly over the bars, and wood fed to
enliven the fire and promote the draught.
The blower or blast pipe is then set going, and coal gradually fed a
little at a time, evenly distributed, covering those parts the most
where the fire burns through the most brightly.
A steady fire is better than one that is forced, because the combustion
is more perfect and less clinker is formed, hence less cleaning will be
necessary, and the fire door will not be kept open so long to let in
cold air. This is important because a steady temperature in the fire box
promotes its durability, as well as giving a uniform boiler pressure.
The strains placed upon a fire box by a fierce fire suddenly cooled by a
heavy charge of coal or of cold air from an open fire door are highly
destructive.
Furthermore, the greatest economy of fuel is attained by keeping the
boiler pressure up, and using the steam expansively by hooking up the
links to shorten the point of cut-off.
A safety valve steadily blowing off steam, whether the engine is running
or not, is a sign of bad firing and wastefulness.
It is the fireman's duty to attend to the fire, but nevertheless a
careful engineer will be as much interested in proper firing as in his
own duties, and as the engineer has more experience than the fireman, he
is warranted in exercising an ordinary supervision on the firing, which
will be welcome to an earnest or ambitious fireman.
The engineer should examine, with a wrench in hand, the bolts and nuts
about the trucks and axle boxes, as these are apt to become loose and
come off on the road. A proper construction would remedy this defect
almost entirely, and by a proper construction is meant the more frequent
employment of split pins, cotters, and other similar safety appliances
now omitted for the sake of economy of manufacture.
Nothing in the future of the locomotive is more certain than improvement
in this respect, and nothing is more urgently needed, as any engineer
will become satisfied if he will gather up along a mile of ordinary
railroad the nuts and washers that lay along the track.
The eccentric straps and the pins in the link motion require an
examination, which may be done while oiling the parts of the engine.
The oiling requires careful attention; first the cups themselves
sometimes become loose, an argument in favor of having, wherever
possible, the cups solid on the parts, as done in European practice.
Oil holes are apt to get choked by gumming, which is that the oil in
time forms into a brown gummy substance that fills the oil hole. Perfect
lubrication does not imply wasteful lubrication by any means, but a
wasteful use of oil is probably less expensive than insufficient
lubrication.
A thorough engineer will use no more oil than is necessary; he will
leave nothing to conjecture or chance, but know from personal inspection
that his engine is in complete working order, and to this end the
lubrication of the working parts is a vital element.
After having oiled the eccentric straps, the link motion and the
reversing gear beneath the engine, the reversing lever and the parts
above the frame must be oiled, and the reversing lever moved back and
forth several times, from end to end of the sector or quadrant, so as to
distribute the oil throughout the joints and working surfaces.
The axle boxes require careful attention in oiling. In English practice,
tallow is packed in the corners of the cavities of the top of the box,
so that if the box should begin to heat the tallow will melt, and afford
extra lubrication with a heavier lubricant than usual, which will often
stop the heating.
The connecting and coupling rods then require attention, the cups being
filled and the lubrication adjusted.
When steam is up the gauge glass should be blown through again, and it
will be found that the water stands higher in the glass than it did
before the boiler was under pressure.
The packing of the piston and of the pump glands, if the engine has
pumps, should be known to be properly set up, bearing in mind that a
leaky pump gland lets air into the pump and impairs its action.
The sand box should contain dry sand, as wet sand will not feed
properly.
If steam is raising too rapidly, close the lower damper to reduce the
consumption of fuel and save blowing off steam through the safety valve,
which should always be avoided as much as possible.
Before starting the engine, open the cylinder cocks and keep them open
until the sound discloses that dry steam, and not steam and water, is
issuing.
Open the throttle enough to start the engine easily and not with a jump,
and be prepared to shut off steam instantly if a blow in any part of the
engine should indicate an obstruction to its working.
In starting a train, the reversing lever is put in the end forward notch
and the cylinder cocks opened. Then the throttle is opened a little at
first, so as to avoid starting with a violent shock that might break the
couplings.
If in starting (or in ascending gradients) the wheels are forced to
slip, the sand lever should be operated, a slight sprinkling of sand
serving better than a heavy one. If the sand is damp, it will fall in
lumps and not distribute evenly as it should do, while at the same time
a great deal more sand will be found necessary.
When the train is fairly under way, the aim should be to maintain full
boiler pressure, so as to keep up the required speed with the links
hooked up to work the steam as expansively as possible, bearing in mind
that the higher up the links are hooked the more expansively the steam
is used, and that therefore less steam is used to do the work and the
boiler pressure can be kept up easier.
To understand this clearly, let it be supposed that the steam pressure
in the boiler is 90 lbs. per square inch, and that the piston area is
400 inches, and the total pressure impelling the piston will be 36,000
lbs.; if this follows the piston for 22 inches, the power becomes
792,000 inch lbs. per stroke.
Now suppose the pressure is 150 lbs. per square inch, and this
multiplied by the piston area (400) gives 60,000 lbs. impelling the
piston, and this would require to follow the piston but 13.2 inches in
order to give 792,000 inch lbs. In the one case we have 22 inches, and
in the other 13.2 inches of the cylinder to fill with steam. Of course
it will take more fuel under the heat of firing to keep the pressure up
to the 150 lbs.; but on the other hand, when the steam is cut off in the
cylinder there will be 160 lbs. per square inch in it, and all the work
that this does in expanding is gained during the rest of the stroke, so
that the required amount of power would be obtained by cutting off
earlier than at 13 inches.
The water should, under ordinary conditions, be kept at an uniform level
in the boiler. Steam can of course be made quicker with a small than
with a large quantity of water, but the smaller the quantity of water
the more the steam pressure is liable to fluctuate, and the closer the
firing must be attended to.
Furthermore, the more water there is in the boiler, the greater the
safety, because the longer the boiler can go without feeding, and, if
the pumps or injectors, as the case may be, should act imperfectly,
there is more time to get them working properly.
In testing the water level, the gauge glass alone is not to be entirely
depended upon, hence the gauge cocks should be opened. The water should
not be allowed to go below the middle gauge cock.
It is obvious that when the water is below a certain gauge cock, the
gauge glass only can give any information as to how far it is below it,
hence it must be used for this purpose.
When using it, it should be blown through by opening its lower cock, and
if there is any doubt about its showing the proper water level it should
be blown through two or three times, watching the level of the water in
the glass at each trial.
A constant boiler feeding is the best, as it is more conducive to a
uniform boiler pressure and temperature.
The fire should be fed in small charges, the fire door being kept open
as little as possible, because a high temperature in the firebox is
necessary to perfect combustion. If heavy charges of coal are given at
once, then for some time the fire box will be cooled, and then, as the
fire burns through, a fierce heat will be generated. This alternate
heating and cooling is very destructive to the fire box and the tubes,
as it causes an expansion and contraction that rack the joints and
seams.
There are several ways of firing, each having its advocate. Upon the
following points, however, there is no dispute. First, a slow combustion
is the most perfect, because it produces less clinker, which saves fuel
and also saves a large amount of fire cleaning and therefore of
admission of cold air to the fire box. A high temperature is necessary
to combustion, and the temperature of the fuel is most difficult to keep
up at the sides of the fire box.
By light and frequent firing the bright fire will never be covered up,
hence the temperature will be maintained. This favors an even
distribution over a large surface of the fire of each shovelful of coal.
But if at any point the draught is lifting the fire, and small bright
pieces of fire are lifting up, it is an evidence that the fire is
thinnest there or else that the bars are cleanest there. In either case,
an extra amount of coal is required at that spot.
Some engineers will charge one side of the fire box lightly and then the
other, this being done so as to keep up the temperature in the fire box.
Others will fire first the front and then the back of the box, which
answers the same purpose, but in no case should the charge be heavy.
A fireman may become so accustomed to the road and his engine, that
under some conditions he may fire when he reaches certain points on the
road, regulating it like clockwork.
On a trip from Philadelphia to Reading, on an engine having a Wooten
fire box (whose special feature is a large fire box, which enables slow
combustion), the firing was conducted as follows:
The fire was was not fed or touched until just before reaching
Bridgeport, 18 miles from Philadelphia, when a thin layer of coal Was
spread evenly on the fire. Eleven miles were then made without opening
the fire door, the next firing taking place just before reaching
Phoenixville.
Ten miles were run before the next firing, which occurred just before
arriving at Pottstown.
The next firing occurred at Bordenboro', three miles from Pottstown. The
remaining 8 miles were made without firing. The steam pressure did not
vary more than 10 lbs. per square inch during the trip.
On a trip from New York to Philadelphia by the lightning express train
the firing was conducted as follows:
The coal was anthracite and in lumps from 5 to 7 inches in diameter; at
one end it reached up to the level of the fire door, while at the tube
plate end of the fire box it was about 6 inches deep.
The grate bars were constructed to shake in three sections, and shaking
the bars to clear out the fire caused it to feed forward of itself, and
the combustion of the coal caused it to break up into lumps about 2
inches in diameter at the tube plate, where the fire was much brighter
than at the fire door end. The steam pressure varied about 10 lbs.
during the trip.
We now come to the best times to fire, to feed, and to oil the valves,
and this depends on the level of the road.
On a level road these matters could be attended to with regularity, but
as the engine has most work to do in ascending inclines, it is necessary
to prepare for such emergencies: First, by having a good fire prepared,
so that the fire door may be kept closed as much as possible while the
engine is ascending; second, by having plenty of water in the boiler, so
as to keep steam, without feeding any more than possible when the engine
is calling for more steam, by reason of the reversing lever being put
over towards full gear.
The speed is kept well up before reaching the incline, and the reversing
lever moved forward a notch or two at a time to maintain the speed,
while at the same time moving the sand lever to feed the sand as soon as
the engine speed shows signs of reducing.
ACCIDENTS ON THE ROAD.
The accidents to which the locomotive is most liable when running upon
the road, and the course to be pursued by the engineer to enable him to
take the engine to the depot or complete the trip, are as follows:
KNOCKING OUT THE FRONT CYLINDER HEAD OR COVER.--This arises from various
causes, such as a breakage of a connecting rod strap, or of a piston rod
or cross head. It is the practice of some locomotive builders to cut in
the cylinder cover flange a small groove close to the part that fits the
cylinder bore, so that the cover shall break out in the form of a disc,
leaving the cover, flange, bolts, and nuts intact, and diminishing the
liability to break the cylinder itself as well as the cover.
The provisional remedy for this accident is to take off the connecting
rod (on the side of the broken cover) and also the valve motion, either
at the rock shaft arm or by taking down the eccentric rod straps. Then
place the valve in the centre of its travel so that it shall cover and
enclose both the cylinder steam ports and leave the exhaust port open.
Then block the cross head firmly on the forward centre, and go ahead
with the other cylinder.
HEATING OF PISTON RODS.--This the engineer can often discover by sight,
or by smelling it from the cab. The remedy is to stop the engine and
slack back the gland until the steam from the engine cylinder leaks
freely through the packing. Then apply a little extra lubrication or
water while _running slowly_.
BREAKING OF A PISTON ROD.--If the piston rod breaks, but does not knock
out the cylinder head or cover, pursue the same course as directed for
breaking the cylinder cover, taking the additional precaution to block
the piston, which may be done by fitting pieces of wood between the
guide bars, making the pieces long enough to fit between the cross head
and guide yoke.
The cylinder or waste water cocks on the side of the accident must also
be opened, to prevent any leakage of steam past the slide valve from
getting into the cylinder and driving the piston against the cylinder
cover, and breaking the cylinder cover or even the cylinder itself.
If the piston rod breaks from the cross head, it is safest to remove it
from the cylinder, though this is unnecessary, if it be securely blocked
against the cylinder head so that it cannot move, though steam may leak
in on either side of it.
BREAKING A CRANK PIN.--This is a somewhat frequent accident, but seldom
takes place on both sides of the engine at once.
The remedy is to take off all the parallel or coupling rods, and if it
is the crank pin on the driving wheels which breaks, take off the
connecting rod also, and securely block the cross head, disconnecting
the valve motion as before directed, and opening the cylinder waste
water cocks. In the case of this accident occurring, it is absolutely
essential to take off the parallel rods on both sides of the engine, or
otherwise the crank pins on the other side are apt to break.
THROWING OFF A WHEEL TIRE.--In this case the best plan is to block the
tireless wheel entirely clear of the track, which may be done by putting
a block of wood into the oil cellar of the driving box, and then tow the
engine to the repair shop; for if the engine is run to the shop, and the
wheel touches the rail, it will impair its diameter for the proper size
of tire.
THROWING OFF A DRIVING WHEEL.--This is not a common accident, but
nevertheless it sometimes occurs; they break usually just outside of the
driving axle box. In this case take out the driving box and fit in its
place a block of wood affording journal bearing for the axle. Let this
block rest on the pedestal cap, holding the axle up in the centre of the
pedestal. Then secure the piston and disconnect the valve gearing and
open the cylinder cocks as before, and the engine can be run _slowly_ to
the repair shop without danger of further accident, or, if convenient,
it can be towed by another engine.
BREAKING A SPRING OR SPRING HANGER.--Lift the engine with the jacks
until the driving wheel axle box is about in the centre of the pedestal,
and put any convenient piece of iron across the top of the driving axle
box and between it and the engine frame, thus taking the weight of the
engine on the frame instead of on the spring. Place also a block of iron
between the end of the equalizing bar and the top of the engine frame,
so as to prevent the movement of the equalizing bar, and to allow the
spring at the other end of the equalizing bar to operate without moving
the said bar. Every engineer should carry in his tool box pieces of
metal suitable for this purpose, because this is a frequent accident. It
does not, however, materially affect the working of the engine, and
should not delay a train more than a few minutes.
BURSTED FLUES AND TUBES.--These are usually plugged by tapering a piece
of pine wood and driving it into the bursted tube by means of an iron
bar. Taper iron plugs are often carried, and then driven into the end of
the tube after the wooden one has been driven in. To enable this job to
be done, it is necessary to thickly cover the fire with green coal,
which operates to cool the tubes and prevent the loss of the water in
the boiler. Sometimes careful engineers prepare for use pine plugs
turned slightly taper, and a little slack, for the inside of the tube.
In case of leak, this plug is inserted in the flue, and driven along it
until it covers the fracture, the expansion due to its saturation
causing it to become locked in the tube.
SLIPPING OF ECCENTRICS.--Place the reverse lever in the forward notch of
the sector. Place the crank on its forward dead centre, as near as can
be judged by the eye, and loosen the set screw of the forward eccentric,
that is to say, the eccentric which connects to the upper end of the
link. Move that eccentric round upon the axle until the slide valve
leaves the steam port at the front end of the cylinder open to the
amount of required valve lead. In moving the eccentric round upon the
shaft, move it in the direction in which it will rotate when the engine
is running forward, so as to allow for and take up any lost motion there
may be in the eccentric straps, in the eccentric rod eyes and bolts, and
in the other working parts of the valve gear; for if the eccentric was
moved backward, all such lost motion would operate to vitiate the set of
the valve. The eccentric being placed as directed fastens its set screw
securely.
If the backward eccentric is the loose one, throw the reverse lever to
the backward notch of the sector, lifting the link up so that the
eccentric connected to the lower end of the link may be approximately
adjusted by moving it around upon the axle in the direction in which it
will rotate when the engine is running backward, until the back cylinder
port is open to the amount of the valve lead. Another very ready plan of
temporarily adjusting the eccentrics is as follows: Place the reverse
lever in the end notch forward, and place the engine crank or driving
crank pin as near on a dead centre as the eye will direct, and open both
the cylinder waste water cocks. Then disconnect the slide valve spindle
from the rocker arm, and move the slide valve spindle until the opening
of the cylinder steam port corresponding to the end of the cylinder at
which the piston stands will be shown by steam blowing through the waste
water cock at that end of the cylinder; the throttle valve being opened
but a trifle, to allow a small steam supply to enter the steam chest and
cylinder, for if much steam is admitted, it may pass through a leak in
the piston and blow through both the waste water cylinder cocks.
The position of the valve being thus determined, the eccentric must be
moved upon the driving axle until the valve spindle will connect with
the rocker arm without being moved, or moving the valve at all.
HOT AXLE BOXES.--If not convenient to reduce the speed of the engine, or
if that and free lubrication do not cool the box, a plentiful supply of
cold water should be administered, it being well to have at hand a small
hose pipe, by means of which water from the tender tank can be used. If
the brasses have Babbitt metal in them and it should melt, it is better,
if possible, to cool the axle box while the engine is moving, which will
injure the journal less than if the journal is stopped to cool the box,
because in the latter case the brass or box is apt to become soldered to
the journal of the axle, and when the engine is again started, the
cutting or abrasion will recommence with extreme violence.
BREAKING A LIFTING LINK OR THE SADDLE PIN THAT CONNECTS THE SLOT LINK TO
THE REVERSE SHAFT.--Cut a piece of wood and tie it into the slot of the
link, over the link block or die, making it of a length to keep the link
in the position for hauling the train. Then fasten another piece of wood
in the link slot beneath the sliding block or die, thus securing that
die in the proper position for the engine to go ahead. In this case, the
engineer must be careful in stopping, as he cannot reverse the engine on
the crippled side.
Secondary accidents are almost sure to occur if a disconnected piston is
not securely blocked in the cylinder, or from blocking the piston aright
and attempting to let the slide valve run, or from attempting to run
with the parallel rods on one side only disconnected. There are numerous
accidents, which only common sense and a familiarity with the locomotive
can provide a temporary remedy for, but those here enumerated are by far
the most common.
ADJUSTING THE PARTS OF A LOCOMOTIVE.
When the wedges of the axle boxes are to be adjusted for fit to the
pedestal shoes, the engine should be moved until the coupling rods on
one side of the engine are in line with the piston rod, because in this
position the rod will, to a certain extent, act as a guide in keeping
the axles parallel to each other, and at a right angle to the line of
engine centres.
Bear in mind that the distance from the centre to centre of axle boxes
must be the same as the distance from centre to centre of the crank
pins, and that when the coupling or side rods are in line with the
piston rod, they act to resist the axle boxes from being set up too
close together.
[Illustration: Fig. 3350.]
The importance of a proper adjustment of the axle boxes, coupling boxes,
and connecting rods cannot be overestimated, and it is necessary
therefore to explain it thoroughly. In Fig. 3350, then, _s_, _s_
represent two wheel axles, whose boxes are between their wedges. At S,
S´ are the screws for setting up the shoes or wedges W and W´
respectively. The axles are shown on the line of centres C, C of the
engine, the piston being at the head end of the cylinder, and the crank
pins on the line of centres as denoted by the small black circles. The
wedges W and W´ are shorter than the leg of the pedestal, so that they
may be set up by the set screws S and S´, and take up the wear.
In some engines the wedges V and V´ are also shorter for the same
purpose. Now it is clear that setting up the screws S and S´ will move
the axles _s_, _s´_ to the left, and this will alter the clearance
between the piston when it is at the end of the stroke and the cylinder
cover.
It is clear that the distance between the centres of the two axles must
be the same as the distance between the centres of the two crank pins,
or else the frame will be subjected to a great strain, tending to break
the crank pins and the side rods.
In order to keep the clearance equal and to know when it is equal, it is
necessary, at some time when the cylinder cover at the head end is off,
to disconnect the connecting rod and push the piston clear up against
the left hand cylinder cover, and from the cross head as a guide, make
on the side of the guide a line L´. Then put on the cylinder cover at
the head end and push the piston up against it and mark a line L. Then
when the connecting rod is put on again, the wheels may be moved around
if the engine is jacked up, or, if not, the engine may be moved along
the rails with a pinch bar, and the clearance will be equal when the
cross head (at the ends of the stroke) comes within an equal distance of
the respective lines L´, L when the crank is on the dead centres, and it
is well to adjust the wedges W W´ so that the cross head does travel
within an equal distance, and mark on the guide bar two more lines, one
at each end of the bar.
These lines are a permanent guide in setting up the shoes or wedges, and
lining up the connecting rods, and coupling or side rods, because it is
clear that from the method employed in marking them the distance between
the end of the cross head, when at the end of its stroke, and the line
L, and that between the face of the piston and the cylinder cover, will
be equal.
A proper adjustment, therefore, should be made as follows: The piston
should be at the end of its stroke, the crank pins being on the line of
centres.
Screw S should be operated to set up the wedge W, taking up the wear of
the sides of the box, and bringing the edge of the cross head the proper
distance from the line L. The connecting rod brasses should then be set
up to fit the pins, and the screw S´ operated to set up wedge W´ to have
easy contact with the side of its axle box. If, however, there has been
so much wear on the axle boxes that they are still too loose between the
wedges, both wedges may be set up to take up this wear, since it is more
important to have the axle boxes a proper fit between the wedges than it
is to maintain an exactly equal amount of clearance at each end of the
cylinder.
The engine will then be in proper tram on this side, or, in other words,
the distance from the centre to centre of the crank pins will be the
same as that from centre to centre of the axles.
On the other side of the engine the process is the same, the engine
being moved until the crank pins are on the line of centres C C and the
wedges set up according to the lines.