of the paddle shaft journal 4-3/8 inches; the length of the journal in each
case is 5 inches. The diameter of the large eye of the crank is 7 inches,
and the diameter of the hole through it is 4-3/8 inches; the diameter of
the small eye of the crank is 5-1/4 inches, the diameter of the hole
through it being 3 inches. The depth of the large eye is 4-1/4 inches, and
of the small eye 3-3/4 inches; the breadth of the web is 4 inches at the
shaft end, and 3 inches at the pin end, and the thickness of the web is
2-5/8 inches. The width of the notch forming the crank in the intermediate
shaft for working the air pump is 3-1/2 inches, and the width of each of
the arms of this crank is 3-15/16 inches. Both the outer and inner corners
of the crank are chamfered away, until the square part of the crank meets
the round of the shaft. The method of securing the cranks pins into the
crank eyes of the intermediate shaft consists in the application of a nut
to the end of each pin, where it passes through the eye, the projecting end
of the pin being formed with a thread upon which the nut is screwed.
629. _Q._--Will you describe the eccentric and eccentric rod?
[Illustration: Fig. 51. ECCENTRIC AND ROD. Messrs. Penn.]
_A._--The eccentric and eccentric rod are shown in fig. 51. The eccentric
is put on the crank shaft in two halves, joined in the diameter of largest
eccentricity by means of a single bolt passing through lugs on the central
eye, and the back balance is made in a separate piece five eighths of an
inch thick, and is attached by means of two bolts, which also help to bind
the halves of the eccentric together. The eccentric strap is half an inch
thick, and 1-1/4 inch broad, and the flanges of the eccentric, within which
the strap works, are each three eighths of an inch thick. The eccentric rod
is attached to the eccentric hoop by means of two bolts passing through
lugs upon the rod, and tapped into a square boss upon the hoop; and pieces
of iron, of a greater or less thickness, are interposed between the
surfaces in setting the valve, to make the eccentric rod of the right
length. The eccentric rod is kept in gear by the push of a small horizontal
rod, attached to a vertical blade spring, and it is thrown out of gear by
means of the ordinary disengaging apparatus, which acts in opposition to
the spring, as, in cases where the eccentric rod is not vertical, it acts
in opposition to the gravity of the rod.
630. _Q._--Will you explain in detail the construction of the valve
gearing, or such parts of it as are peculiar to the oscillating engine?
_A._--The eccentric rod is attached by a pin, 1 inch in diameter, to an
open curved link or sector with a tail projecting upward and passing
through an eye to guide the link in a vertical motion. The link is formed
of iron case-hardened, and is 2-3/4 inches deep at the middle, and 2-3/8
inches deep at the ends, and 1 inch broad. The opening in the link, which
extends nearly its entire length, is 1-5/16 inch broad; and into this
opening a brass block 2 inches long is truly fitted, there being a hole
through the block 3/4 inch diameter, for the reception of the pin of the
valve shaft lever. The valve shaft is 1-3/4 inch diameter at the end next
the link or segment, and diminishes regularly to the other end, but its
cross section assumes the form of an octagon in its passage round the
cylinder, measuring mid-way 1-1/4 inch deep, by about 3/4 inch thick, and
the greatest depth of the finger for moving the valve is about 1 inch. The
depth of the lever for moving the valve shaft is 2 inches at the broad, and
1-1/4 inch at the narrow end. The internal breadth of the mortice in which
the valve finger moves is 5/16 inch, and its external depth is 1-3/4 inch,
which leaves three eighths of an inch as the thickness of metal round the
hole; and the breadth, measuring in the direction of the hole, is 1-1/2
inch. The valve rod is three fourths of an inch in diameter, and the
mortice is connected to the valve rod by a socket 1 inch long, and 1-1/8
inch diameter, through which a small cutter passes. A continuation of the
rod, eleven sixteenths of an inch diameter, passes upward from the mortice,
and works through an eye, which serves the purpose of a guide. In addition
to the guide afforded to the segment by the ascending tail, it is guided at
the ends upon the columns of the framing by means of thin semicircular
brasses, 4 inches deep, passing round the columns, and attached to the
segment by two 3/8 inch bolts at each end, passing through projecting
feathers upon the brasses and segment, three eighths of an inch in
thickness. The curvature of the segment is such as to correspond with the
arc swept from the centre of the trunnion to the centre of the valve lever
pin when the valve is at half stroke as a radius; and the operation of the
segment is to prevent the valve from being affected by the oscillation of
the cylinder, but the same action, would be obtained by the employment of a
smaller eccentric with more lead. In some engines the segment is not formed
in a single piece, but of two curved blades, with blocks interposed at the
ends, which may be filed down a little, to enable the sides of the slot to
be brought nearer, as the metal wears away.
631. _Q._--What kind of plummer blocks are used for the paddle shaft
bearings?
_A._--The paddle shaft plummer blocks are altogether of brass, and are
formed in much the same manner as the cap of the piston rod, only that the
sole is flat, as in ordinary plummer blocks, and is fitted between
projecting lugs of the framing, to prevent side motion. In the bearings
fitted on this plan, however, the upper brass will generally acquire a good
deal of play after some amount of wear. The bolts are worked slack in the
holes, though accurately fitted at first; and it appears expedient,
therefore, either to make the bolts very large, and the sockets through
which they pass very deep, or to let one brass fit into the other.
632. _Q._--How are the trunnion plummer blocks made?
_A._--The trunnion plummer blocks are formed in the same manner as the
crank shaft plummer blocks; the nuts are kept from turning back by means of
a pinching screw passing through a stationary washer. It is not expedient
to cast the trunnion plummer blocks upon the lower frame, as is sometimes
done; for the cylinders, being pressed from the steam trunnions by the
steam, and drawn in the direction of the condenser by the vacuum, have a
continual tendency to approach one another; and as they wear slightly
toward midships, there would be no power of readjustment unless the plummer
blocks were movable. The flanges of the trunnions should always fit tight
against the plummer block sides, but there should be a little play sideways
at the necks of the trunnions, so that the cylinder may be enabled to
expand when heated, without throwing an undue strain upon the trunnion
supports.
633. _Q._--What kind of paddle wheel is supplied with these oscillating
engines?
_A._--The wheels are of the feathering kind, 9 feet 8 inches in diameter,
measuring to the edges of the floats; and there are 10 floats upon each
wheel, measuring 4 feet 6 inches long each, and 18-1/2 inches broad. There
are two sets of arms to the wheel, which converge to a cast iron centre,
formed like a short pipe with large flanges, to which the arms are affixed.
The diameter of the shaft, where the centre is put on, is 4-1/2 inches, the
external diameter of the pipe is 8 inches, and the diameter of the flanges
is 20 inches, and their thickness 1-1/4 inch. The flanges are 12 inches
asunder at the outer edge, and they partake of the converging direction of
the arms. The arms are 2-1/4 inches broad and half an inch thick; the heads
are made conical, and each is secured into a recess upon the side of the
flange by means of three bolts. The ring which connects together the arms,
runs round at a distance of 3 feet 6 inches from the centre, and the
projecting ends of the arms are bent backward the length of the lever which
moves the floats, and are made very wide and strong at the point where they
cross the ring, to which they are attached by four rivets. The feathering
action of the floats is accomplished by means of a pin fixed to the
interior of the paddle box, set 3 inches in advance of the centre of the
shaft, and in the same horizontal line. This pin is encircled by a cast
iron collar, to which rods are attached 1-3/8 inch diameter in the centre,
proceeding to the levers, 7 inches long, fixed on the back of the floats in
the line of the outer arms. One of these rods, however, is formed of nearly
the same dimensions as one of the arms of the wheel, and is called the
driving arm, as it causes the cast iron collar to turn round with the
revolution of the wheel, and this collar, by means of its attachments to
the floats, accomplishes the feathering action. The eccentricity in this
wheel is not sufficient to keep the floats in the vertical position, but in
the position between the vertical and the radial. The diameter of the pins
upon which the floats turn is 1-3/8 inch, and between the pins and paddle
ring two stud rods are set between each of the projecting ends of the arms,
so as to prevent the two sets of arms from being forced nearer or further
apart; and thus prevent the ends of the arms from hindering the action of
the floats, by being accidentally jammed upon the sides of the joints.
Stays, crossing one another, proceed from the inner flange of the centre to
the outer ring of the wheel, and from the outer flange of the centre to the
inner ring of the wheel, with the view of obtaining greater stiffness. The
floats are formed of plate iron, and the whole of the joints and joint pins
are steeled, or formed of steel. For sea-going vessels the most approved
practice is to make the joint pins of brass, and also to bush the eyes of
the joints with brass; and the surface should be large to diminish wear.
634. _Q._--Can you give the dimensions of any other oscillating engines?
_A._--In Messrs. Penn's 50 horse power oscillating engine, the diameter of
the cylinder is 3 feet 4 inches, and the length of the stroke 3 feet. The
thickness of the metal of the cylinder is 1 inch, and the thickness of the
cylinder bottom is 1-3/4 inch, crossed with feathers, to give it additional
stiffness. The diameter of the trunnion bearings is 1 foot 2 inches, and
the breadth of the trunnion bearings 5-1/2 inches. Messrs. Penn, in their
larger engines, generally make the area of the steam trunnion less than
that of the eduction trunnion, in the proportion of 32 to 37; and the
diameter of the eduction trunnion is regulated by the internal diameter of
the eduction pipe, which is about 1/5th of the diameter of the cylinder.
But a somewhat larger proportion than this appears to be expedient: Messrs.
Rennie make the area of their eduction pipes, in oscillating engines, 1/22d
of the area of the cylinder. In the oscillating engines of the Oberon, by
Messrs. Rennie, the cylinder is 61 inches diameter, and 1-1/2 inch thick
above and below the belt, but in the wake of the belt it is 1-1/4 inch
thick, which is also the thickness of metal of the belt itself. The
internal depth of the belt is 2 feet 6 inches, and its internal breadth is
4 inches. The piston rod is 6-3/4 inches in diameter, and the total depth
of the cylinder stuffing box is 2 feet 4 inches, of which 18 inches
consists of a brass bush--this depth of bearing being employed to prevent
the stuffing box or cylinder from wearing oval.
635. _Q._--Can you give any other examples?
_A._--The diameter of cylinder of the oscillating engines of the steamers
Pottinger, Ripon, and Indus, by Miller & Ravenhill, is 76 inches, and the
length of the stroke 7 feet. The thickness of the metal of the cylinder is
1-11/16 inch; diameter of the piston rod 8-3/4 inches; total depth of
cylinder stuffing box 3 feet; depth of bush in stuffing box 4 inches; the
rest of the depth, with the exception of the space for packing, being
occupied with a very deep gland, bushed with brass. The internal diameter
of the steam pipe is 13 inches; diameter of steam trunnion journal 25
inches; diameter of eduction trunnion journal 25 inches; thickness of metal
of trunnions 2-1/4 inches; length of trunnion bearings 11 inches;
projection of cylinder jacket, 8 inches; depth of packing space in
trunnions, 10 inches; width of packing space in trunnions, or space round
the pipes, 1-1/2 inch; diameter of crank pin 10-1/4 inches; length of
bearing of crank pin 15-1/2, inches. There are six boilers on the tubular
plan in each of these vessels; the length of each boiler is 10 feet 6
inches, and the breadth 8 feet; and each boiler contains 62 tubes 3 inches
in diameter, and 6 feet 6 inches long, and two furnaces 6 feet 4-1/2 inches
long, and 3 feet 1-1/2 inch broad.
636. _Q._--Is it the invariable practice to make the piston rod cap of
brass in the way you have described?
_A._--In all oscillating engines of any considerable size, the cover of the
connecting brass, which attaches the crank pin to the connecting rod, is
formed of malleable iron; and the socket also, which is cuttered to the end
of the piston rod, is of malleable iron, and is formed with a T head,
through which bolts pass up through the brass, to keep the cover of the
brass in its place.
637. _Q._--Is the piston of an oscillating engine made deeper than in
common engines?
_A._--It is expedient, in oscillating engines, to form the piston with a
projecting rim round the edge above and below, and a corresponding recess
in the cylinder cover and cylinder bottom, whereby the breadth of bearing
of the solid part of the metal will be increased, and in many engines this
is now done.
638. _Q._--Would any difficulty be experienced in keeping the trunnions
tight in a high pressure oscillating engine?
_A._--It is very doubtful whether the steam trunnions of a high pressure
oscillating engine will continue long tight if the packing consists of
hemp; and it appears preferable to introduce a brass ring, to embrace the
pipe, cut spirally, with an overlap piece to cover the cut, and packed
behind with hemp.
639. _Q._--How is the packing of the trunnions usually effected?
_A._--The packing of the trunnions, after being plaited as hard as
possible, and cut to the length to form one turn round the pipe, is dipped
into boiling tallow, and is then compressed in a mould, consisting of two
concentric cylinders, with a gland forced down into the annular space by
three to six screws in the case of large diameters, and one central screw
in the case of small diameters. Unless the trunnion packings be well
compressed, they will be likely to leak air, and it is, therefore,
necessary to pay particular attention to this condition. It is also very
important that the trunnions be accurately fitted into their brasses by
scraping, so that there may not be the smallest amount of play left upon
them; for if any upward motion is permitted, it will be impossible to
prevent the trunnion packings from leaking.
DIRECT ACTING SCREW ENGINE.
640. _Q._--Will you describe the configuration and construction of a direct
acting screw engine?
_A._--I will take as an example of this species of engine, the engine
constructed by Messrs. John Bourne & Co., for the screw steamer Alma, a
vessel of 500 tons burden. This engine is a single steeple engine laid on
its side, and in its general features it resembles the engines of the
Amphion already described, only that there is one cylinder instead of two.
The cylinder is of 42 inches diameter and 42 inches stroke, and the vessel
has been propelled by this single engine at the rate of fourteen miles an
hour.
641. _Q._--Is not a single engine liable to stick upon the centre so that
it cannot be started or reversed with facility?
_A._--A single engine is no doubt more liable to stick upon the centre than
two engines, the cranks of which are set at right angles with one another;
but numerous paddle vessels are plying successfully that are propelled by a
single engine, and the screw offers still greater facility than paddles for
such a mode of construction. In the screw engine referred to, as the
cylinder is laid upon its side, there is no unbalanced weight to be lifted
up every stroke, and the crank, whereby the screw shaft is turned round,
consists of two discs with a heavy side intended to balance the momentum of
the piston and its connections; but these counter-weights by their
gravitation also prevent the connecting rod and crank from continuing in
the same line when the engine is stopped, and in fact they place the crank
in the most advantageous position for starting again when it has to be set
on.
642. _Q._--Will you explain the general arrangement of the parts of this
engine?
_A._--The cylinder lies on its side near one side of the vessel, and from
the end of the cylinder two piston rods extend to a cross head sliding
athwartships, in guides, near the other side of the vessel. To this cross
head the connecting rod is attached, and one end of it partakes of the
motion of the cross head or piston, while the other end is free to follow
the revolution of the crank on the screw shaft.
643. _Q._--What is the advantage of two discs entering into the composition
of the crank instead of one?
_A._--A double crank, such as two discs form with the crank pin, is a much
steadier combination than would result if only one disc were employed with
an over-hung pin. Then the friction on the neck of the shaft is made one
half less by being divided between the two bearings, and the short
prolongation of the shaft beyond the journal is convenient for the
attachment of the eccentrics to work the valves.
644. _Q._--Will you enumerate some of the principal dimensions of this
engine?
_A._--The bottom frame, on which also the condenser is cast, forms the base
of the engine: on one end of it the cylinder is set; on the other end are
the guides for the cross head, and in the middle are the bearings for the
crank shaft. The part where the cylinder stands is two feet high above the
engine platform, and the elevation to the centre of the guides or the
centre of the shaft is 10 inches higher than this. The metal both of the
side frames and bottom flange is 1-1/4 inch thick. The cylinder has flanges
cast on its sides, upon which it rests on the bottom frame, and it is sunk
between the sides of the frame so as to bring the centre of the cylinder in
the same plane as the centre of the screw shaft. The opening left at the
guides for the reception of the guide blocks is 6 inches deep, and the
breadth of the bearing surface is 11 inches. The cover of the guides is 8
inches deep at the middle, and about half the depth at the ends, and holes
are cored through the central web for two oil cups on each guide. The brass
for each of the crank shaft bearings is cut into four pieces so that it may
be tightened in the up and down direction by the bolts, which secure the
plummer block cap, and tightened in the athwartship direction, which is the
direction of the strain, by screwing up a wedge-formed plate against the
side of the brass, a parallel plate being applied to the other side of the
brass, which may be withdrawn to get out the wedge piece when the shaft
requires to be lifted out of its place. The air pump is bolted to one side
of the bottom frame, and a passage is cast on it conducting from the
condenser to the air pump. In this passage the inlet and outlet valves at
each end of the air pump are situated, and appropriate doors are formed
above them to make them easily accessible. The outlet passage leading from
the air pump communicates with the waste water pipe, through which the
water expelled by the air pump is discharged overboard.
645. _Q._--Is the cylinder of the usual strength and configuration?
_A._--The cylinder is formed of cast iron in the usual way, and is 1-1/8
inch thick in the barrel. The ends are of the same thickness, but are each
stiffened with six strong feathers. The piston is cast open. The bottom of
it is 5/8ths of an inch thick, and it is stiffened by six feathers 3/4 of
an inch thick; but the feather connecting the piston rod eyes is 1-1/4 inch
thick, and the metal round the eyes is 2 inches thick. The piston is closed
by a disc or cover 5/8ths of an inch thick, secured by 15 bolts, and this
cover answers also the purpose of a junk ring. The piston packing consists
of a single cast iron ring 3-1/2 inches broad, and 1/2 inch thick, packed
behind with hemp. This ring is formed with a tongue piece, with an indented
plate behind the cut; and the cut is oblique to prevent a ridge forming in
the cylinder. The total thickness of the piston is 5-1/2 inches. The piston
rods are formed with conical ends for fitting into the piston, but are
coned the reverse way as in locomotives, and are secured in the piston by
nuts on the ends of the rods, these nuts being provided with ratchets to
prevent them from unscrewing accidentally.
646. _Q._--What species of slide valve is employed?
_A._--The ordinary three ported valve, and it is set on the top of the
cylinder. The cylinder ports are 4-1/2 inches broad by 24 inches long; and
to relieve the valve from the great friction due to the pressure on so
large a surface, a balance piston is placed over the back of the valve, to
which it is connected by a strong link; and the upward pressure on this
piston being nearly the same as the downward pressure on the valve, it
follows that the friction is extinguished, and the valve can be moved with
great case with one hand. The balance piston is 21 inches in diameter. In
the original construction of this balance piston two faults were committed.
The passage communicating between the condenser and the top of the balance
piston was too small, and the pins at the ends of the link connecting the
valve and balance piston were formed with an inadequate amount of bearing
surface. It followed from this misproportion that the balance piston, being
adjusted to take off nearly the whole of the pressure, lifted the valve off
the face at the beginning of each stroke. For the escape of the steam into
the eduction passage momentarily impaired the vacuum subsisting there, and
owing to the smallness of the passage leading to the space above the
balance piston, the vacuum subsisting in that space could not be impaired
with equal rapidity. The balance piston, therefore, rose by the upward
pressure upon it momentarily predominating over the downward pressure on
the valve; but this fault was corrected by enlarging the communicating
passage between the top of the balance piston and the eduction pipe. The
smallness of the pins at the ends of the link connecting the valve and
balance piston, caused the surfaces to cut into one another, and to wear
very rapidly, and the pins and eyes in this situation should be large in
diameter, and as long as they can be got, as they are not so easily
lubricated as the other bearings about the engine, and are moreover kept at
a high temperature by the steam. The balance piston is packed in the same
way as the main piston of the engine. Its cylinder, which is only a few
inches in length, is set on the top of the valve casing, and a trunk
projects upwards from its centre to enable the connecting link to rise up
in it to attain the necessary length.
[Illustration: Fig 52. CONNECTING ROD. Messrs. Bourne & Co.]
647. _Q._--What is the diameter of the piston rods and connecting rod?
_A._--The piston rods, which are two in number, are 3 inches diameter, and
12 feet 10 inches long over all. They were, however, found to be rather
small, and have since been made half an inch thicker. The connecting rod
consists of two rods, which are prolongations of the bolts that connect the
sides of the brass bushes which encircle the crank pin and cross head. The
connecting rod is shown in perspective in fig. 52. The rods composing it
are each 2-3/4 inches in diameter.
648. _Q._--Will you describe the configuration of the cross head.
_A._--The cross head, exhibited in fig. 53, is a round piece of iron like a
short shaft, with two unequal arms keyed upon it, the longer of which _b_
works the air pump, and the shorter _c_ works the feed pump. The piston
rods enter these arms at _a A._ The cross head is 8 inches diameter where
it is embraced by the connecting rod at _e_, and 7 inches diameter where
the air pump and feed pump arms are fixed on. The ends of the cross head _d
d_, for a length of 12 inches, are reduced to 3 inches diameter where they
fit into round holes in the centre of the guide blocks. Those blocks are of
cast iron 6 inches deep, 11 inches wide, and 14 inches long, and they are
formed with flanges 1 inch thick on the inner sides of the blocks. The
projection of the air pump lever from the centre of the cross head is 1
foot 9 inches, and it is bent 5-3/4 inches to one side to enable it to
engage the air pump rod. The eye of this arm is 6 inches broad and about 2
inches thick. At the part where one of the piston rods passes through it,
the arm is 8 inches deep and 6 inches wide; but the width thereafter
narrows to 3 inches, and finally to 2 inches; and the depth of the web of
the arm reduces from 8 inches at the piston rod, to 4 inches at the eye,
which receives the end of the air pump rod. The feed pump arm is only 3
inches thick, and has 9 inches of projection from the centre of the cross
head; but the eye attached to it on the opposite side of the cross head for
the reception of the other piston rod is of the same length as that part of
the air pump arm which one of the piston rods passes through. The piston
rods have strong nuts on each side of each of these arms to attach them to
the arms, and also to enable the length of the piston rods to be suitably
adjusted, to leave equal clearance between the piston and each end of the
cylinder at the termination of the stroke.
[Illustration: Fig. 53.
CROSS HEAD AND PUMP ARMS. Messrs. Bourne & Co.]
649. _Q._--Will you recapitulate the main particulars of the air pump?
_A._--The air pump is made of brass 12-1/2 inches diameter and 42 inches
stroke, and the metal of the barrel is 9/16ths of an inch thick. The air
pump bucket is a solid piston of brass, 6-1/2 inches deep at the edge, and
7 inches deep at the eye; and in the edge three grooves are turned to hold
water which answers the purpose of packing. The inlet and outlet valves of
the air pump consist of brass plates 1/2 inch with strong feathers across
them, and in each plate there are six grated perforations covered by india
rubber discs 7 inches in diameter. These six perforations afford
collectively an area for the passage of the water equal to the area of the
pump. The air pump rod is of brass, 2-1/2 inches diameter.
650. _Q._--What are the constructive peculiarities of the discs and crank
pin?
_A._--The discs, which are 64 inches diameter, are formed of cast iron, and
are 2-1/2 inches thick in the body, and 5 inches broad at the rim. The
crank shaft is 8-1/2 inches diameter, and the central boss of the disc
which receives the shaft measures 10 inches through the eye, and the metal
of the eye is 3 inches thick. In the part of the disc opposite to the crank
pin, the web is thickened to 10 inches for nearly the whole semicircle,
with the view of making that side of the disc heavier than the other side;
and when the engine is stopped, the gravitation of this heavy side raises
the crank pin to the highest point it can attain, whereby it is placed in
mid stroke, and cannot rest with the piston rods and connecting rod in a
horizontal line. The crank pin is 8-1/2 inches diameter, and the length of
the bearing or rubbing part of it is 16 inches. It is secured at the ends
to the discs by flanges 18 inches diameter, and 2 inches thick. These
flanges are indented into thickened parts of the discs, and are each
attached to its corresponding disc by six bolts 2 inches diameter,
countersunk in the back of the disc, and tapped into the malleable iron
flange. Besides this attachment, each end of the pin, reduced to 4-1/2
inches diameter, passes through a hole in its corresponding disc, and the
ends of the pin are then riveted over. The crank pin is perforated through
the centre by a small hole about 3/4 of an inch in diameter, and three
perforations proceed from this central hole to the surface of the pin. Each
crank shaft bearing is similarly perforated, and pipes are cast in the
discs connecting these perforations together. The result of this
arrangement is, that a large part of the oil or water fed into the bearings
of the shaft is driven by the centrifugal action of the discs to the
surface of the crank pin, and in this way the crank pin may be oiled or
cooled with water in a very effectual manner. To intercept the water or oil
which the discs thus drive out by their centrifugal action, a light paddle
box or splash board of thin sheet brass is made to cover the upper part of
each of the discs, and an oil cup with depending wick is supported by the
tops of these paddle boxes, which wick is touched at each revolution of the
crank by a bridge standing in the middle of an oil cup attached to the
crank pin. The oil is wiped from the wick by the projecting bridge at each
revolution, and subsides into the cup from whence it proceeds to lubricate
the crank pin bearing. This is the expedient commonly employed to oil the
crank pins of direct acting engines; but in the engine now described, there
are over and above this expedient, the communicating passages from the
shaft bearings to the surface of the pin, by which means any amount of
cooling or lubrication can be administered to the crank pin bearing,
without the necessity of stopping or slowing the engine.
[Illustration: Fig. 54. DOUBLE DISC CRANK. Messrs. Bourne & Co.]
651. _Q._--What is the diameter of the screw shaft?
_A._--The screw shaft is 7-1/2 inches diameter, but the bearings on each
side of the disc are 8-1/2 inches diameter, and 16 inches long. Between the
side of the disc and the side of the contiguous bearings there is a short
neck extending 4-3/4 inches in the length of the shaft, and hollowed out
somewhat to permit the passage of the piston rod; for one piston rod passes
immediately above the shaft on the one side of the discs, and the other
piston rod passes immediately below the shaft on the other side of the
discs. A short piece of one piston rod is shown in fig. 54.
[Illustration: Fig. 55. THRUST BEARING. Messers. Bourne & Co.]
[Illustration: Fig. 56. COUPLING CRANKS. Messers. Bourne & Co.]
652. _Q._--How is the thrust of the screw shaft received?
_A._--The thrust of the screw shaft is received upon 7 collars, each 1 inch
thick, and with 1 inch of projection above the shaft. The plummer block for
receiving the thrust of the shaft is shown in fig. 55, and the coupling to
enable the screw propeller to be disconnected from the engine, so that it
may revolve freely when the vessel is under sail, is shown in fig. 56. When
it is required to disengage the propeller from the engine, the pins passing
through the opposite eyes shown fig. 56, are withdrawn by means of screws
provided for that purpose, and the propeller and the engine are thenceforth
independent of one another.
[Illustration: Fig. 57. LINK MOTION. Messrs. Bourne & Co.]
653. _Q._--Will you describe the arrangement of the valve gearing?
_A._--The end of the screw shaft, after emerging from the bearing beside
the disc, is reduced to a diameter of 4 inches, and is prolonged for 4-1/2
inches to give attachment to the cam or curved plate which gives motion to
the expansion valve. This plate is 3-1/2 inches thick, and a stud 3-1/2
inches diameter is fixed in the plate at a distance of 5 inches from the
centre of the shaft. To this stud an arm is attached which extends to a
distance of 2 inches from the centre of the shaft in the opposite
direction, and the end of this arm carries a pin of 2-1/2 inches diameter.
From the pin most remote from the centre of the shaft, a rod 2-1/2 inches
broad and 1 inch thick extends to the upper end of the link of the link
motion; and from the pin least remote from the centre of the shaft, a
similar rod extends to the lower end of the link of the link motion. This
link, which is represented in fig. 57, is 2-1/4 inches broad, 1 inch thick,
and is capable of being raised or lowered 25 inches in all. In the open
part of the link is a brass block, which, by raising or lowering the link,
takes either the position in which it is represented at the centre of the
link, or a position at either end of it. Through the hole in the brass
block a pin passes to attach the brass to the end of a lever fixed on the
valve shaft; so that whatever motion is imparted to the brass block is
communicated to the valve through the medium of this lever. If the brass
block be set in the middle of the link, no motion is communicated to it,
and the valve being consequently kept stationary and covering both ports,
the engine stops. If the link be lowered until the brass block comes to the
upper end of the link, the valve receives the motion of the eccentric for
going ahead, and the engine moves ahead; whereas if the link be raised
until the brass block comes to the lower end of the link, the valve
receives the motion of the backing eccentric, and the engine moves astern.
Instead of eccentrics, however, pins at the end of the shaft are employed
in this engine, the arrangement partaking of the nature of a double crank;
but the backing pin has less throw than the going ahead pin, whereby the
efficient length of the link for going ahead is increased; and the
operation of backing, which does not require to be performed at the highest
rate of speed, is sufficiently accommodated by about half the throw being
given to the valve that is given in going ahead. A valve shaft extends
across the end of the cylinder with two levers standing up, which engage
horizontal side rods extending from a small cross head on the end of the
valve rod. A lever extends downwards from the end of the valve shaft, which
is connected by a pin to the brass block within the link; and the link is
moved up or down by the starting handle, which, by means of a spring bolt
shooting into a quadrant, holds the starting handle at any position in
which it may be set.
654. _Q._--What is the diameter and pitch of the screw propeller?
_A._--The diameter is 7 feet and the pitch 14 feet. The propeller is Holm's
conchoidal propeller. Its diameter is smaller than is advisable, being
limited by the draught of water of the vessel; and the vessel was required
to have a small draught of water to go over a bar. This engine makes, under
favorable circumstances, 100 strokes per minute. The speed of piston with
this number of strokes is 700 feet per minute, and the engine works
steadily at this speed, the shock and tremor arising from the arrested
momentum of the moving parts being taken away by the counterbalance applied
at the discs.
LOCOMOTIVE ENGINE.
655. _Q._--Will you describe the principal features of a modern locomotive
engine?
_A._--I will take for this purpose the locomotive Snake, constructed by
John V. Gooch for the London and South Western Railway, as an example of a
modern locomotive of good construction, adapted for the narrow gauge. The
length of the wheel base of this engine is 12 feet 8-1/2 inches. There are
two cylinders, each 14-1/4 inches diameter and 21 inches stroke. The total
weight of the engine is 19 tons; and this weight is so distributed on the
wheels as to throw 8 tons on the leading wheels, 6 tons on the driving
wheels, and 5 tons on the hind wheels. The engine is made with outside
cylinders, and the cylinders are raised somewhat out of the horizontal line
to enable them better to clear the leading wheels.
656. _Q._--What are the dimensions of the boiler?
_A._--The interior of the fire box is 3 feet 7-1/4 inches wide by 3 feet
5-1/2 inches long, measuring in the direction of the rails. The area of the
fire grate is consequently 12.4 square feet. The bars are somewhat lower on
the side next the fire door than at the side next the tubes, and the mean
height of the crown of the fire box above the bars is 3 feet 10 inches. The
top edge of the fire door is about 7 inches lower than the crown of the
fire box. The fire box is divided transversely by a corrugated feather or
bridge of plate iron, containing water, about 3-1/2 inches wide, and of
about one-third of the height of the fire box in the centre of the feather,
and about two-thirds the height of the fire box at the sides where it joins
the sides of the fire box. The internal shell of the fire box tapers
somewhat upwards to facilitate the disengagement of the steam. It is about
2 inches narrower and shorter at the top than at the bottom; the water
space between the external and internal shell of the fire box being 2
inches at the bottom and 3 inches at the top.
657. _Q._--Of what material is the fire box composed?
_A._--The external shell of the fire box is formed of iron plates 3/8ths of
an inch thick, and the internal shell is formed of copper plates 1/4 inch
thick, but the tube plate is 3/4 inch thick. The fire grate is rectangular,
and the internal and external shells are tied together by iron stay bolts
3/4 inch diameter, and pitched about 4 inches apart. The roof of the fire
box is stiffened by six strong bars extending from side to side of the fire
box like beams, and the top of the fire box is secured to these bars, so
that it cannot be forced down without breaking or bending them.
658. _Q._--What are the dimensions of the barrel of the boiler?
_A._--The barrel of the boiler is 3 feet 7-1/2 inches in diameter, and 10
feet long. It is formed of iron plates 3/8ths of an inch thick, riveted
together. It is furnished with 181 brass tubes 1-7/8 inch diameter and 10
feet long, secured at the ends by ferules. The tube plate at the smoke box
end is 5/8ths of an inch thick, and the tube plates above the tubes are
tied together by eight iron rods 7/8ths of an inch thick, extending from
end to end of the boiler. The metal of the tubes is somewhat thicker at the
end next the fire, being 13 wire gauge at fire box end, and 14 wire gauge
at smoke box end. The rivets of the boiler are 3/4 inch diameter and 1-1/2
inch pitch. The plating of the ash pan is 5/16ths of an inch thick, and the
plating of the smoke box is 3/16ths of an inch thick.
659. _Q._--Will you describe the structure of the framework on which the
boiler and its attachments rest, and in which the wheels are set?
_A._--The framework or framing consists of a rectangular structure of plate
iron circumscribing the boiler, with projecting lugs or arms for the
reception of the axles of the wheels. In this engine the sides of the
rectangle are double, or, as far as regards the sides, there are virtually
two framings, one for the reception of the driving axles, and the other for
the reception of the axles not connected with the engine. The whole of the
parts of the outer and inner framings are connected together by knees at
the corners, and the double sides are elsewhere connected by intervening
brackets and stays, so as to constitute the whole into one rigid structure.
The whole of the plating of the inside frame is 3/4 inch thick and 9 inches
deep. The plating of the outside frame is of the same thickness and depth
at the fore part, until it reaches abaft the position of the cylinders and
guides, where it reduces to 1/2 inch thick. The axle guard of the leading
wheels is formed of 3/4 plate bolted to the frame with angle iron guides.
The axle guards of the trailing wheels are formed of two 1/2 inch plates,
with cast iron blocks between them to serve as guides. The ends of the
rectangular frame are formed of plates 3/4 thick, and at the front end
there is a buffer beam of oak 4-1/2 inches thick and 15 inches deep. The
draw bolt is 2 inches diameter. There are two strong stays on each side,
joining the barrel of the boiler to the inside framing, and one angle iron
on each side joining the bottom of the smoke box to the inside framing.
660. _Q._--Of what construction are the wheels?
_A._--The wheels and axles are of wrought iron, and the tires of the wheels
are of steel. The driving wheels are 6 feet 6-1/2 inches in diameter, and
the diameter of crank pin is 3-1/2 inches. The diameter of the smaller
wheels is 48-1/2 inches. The axle boxes are of cast iron with bushes of
Fenton's metal, and the leading axle has four bearings. The springs are
formed of steel plates, 3 feet long, 4 inches broad, and 1\2 inch thick.
The axle of the driving wheel has two eccentrics, forged solid upon it, for
working the pumps.
661. _Q._--Will you specify the dimensions of the principal parts of the
engine?
_A._--Each of the cylinders which is 14-1/4 inches diameter, has the valve
casing cast upon it. The steam ports are 13 inches long and 1-5/8 inches
broad, and the exhaust port is 2-1/2 inches broad. The travel of the valve
is 4-1/8 inches, the lap 1 inch, and the lead 1/4 inch. The piston is 4
inches thick: its body is formed of brass with a cover of cast iron, and
between the body and the cover two flanges, forged on the piston rod, are
introduced to communicate the push and pull of the piston to the rod. The
piston rod is of iron, 2-1/2 inches diameter. The guide bars for guiding
the top of the piston rod are of steel, 4 inches broad, fixed to rib iron
bearers, with hard wood 1/4 of an inch thick, interposed. The connecting
rod is 6 feet long between the centres, and is fitted with bushes of white
metal. The eccentrics are formed of wrought iron, and have 4-1/8 inches of
throw. The link of the link motion is formed of wrought iron. It is hung by
a link from a pin attached to the framing; and instead of being susceptible
of upward and downward motion, as in the case of the link represented in
fig. 57 a rod connecting the valve rod with the movable block in the link,
is susceptible of this motion, whereby the same result is arrived at as if
the link were moved and the block was stationary. One or the other
expedient is preferable, according to the general nature of the
arrangements adopted. The slide valve is of brass, and the regulator
consists of two brass slide valves worked over ports in a chest in the
steam pipe, set in the smoke box. The steam pipe is of brass, No. 14. wire
gauge, perforated within the boiler barrel with holes 1/12th of an inch in
diameter along its upper side. The blast pipe, which is of copper, has an
orifice of 4-1/4 inches diameter. There is a damper, formed like a Venetian
blind, with the plates running athwartships at the end of the tubes.
[Illustration: Fig. 58. SAFETY VALVE. Gooch.]
662. _Q._--Of what construction is the safety valve?
_A._--There are two safety valves, consisting of pistons 1-3/16 inch in
diameter, and which are kept down by spiral springs placed immediately over
them. A section of this valve is given in fig. 58.
663. _Q._--What are the dimensions of the feed pumps?
_A._--The feed pumps are of brass, with plungers 4 inches diameter and
3-1/4 inches stroke. The feed pipe is of copper, 2 inches diameter. A good
deal of trouble has been experienced in locomotives from the defective
action of the feed pump, partly caused by the leakage of steam into the
pumps, which prevented the water from entering them, and partly from the
return of a large part of the water through the valves at the return stroke
of the pump, in consequence of the valve lifting too high. The pet cock--a
small cock communicating with the interior of the pump--will allow any
steam to escape which gains admission, and the air which enters by the cock
cools down the barrel of the pump, so that in a short time it will be in a
condition to draw. The most ordinary species of valve in the feed pumps of
locomotives, is the ball valve.
Notwithstanding the excellent performance of the best examples of
locomotive engines, it is quite certain that there is still much room for
improvement; and indeed various sources of economy are at present visible,
which, if properly developed, would materially reduce the expense of the
locomotive power. In all engines the great source of expense is the fuel;
and although the consumption of fuel has been greatly reduced within the
last ten or fifteen years, it is capable of being still further reduced by
certain easy expedients of improvement, which therefore it is important
should be universally applied. One of these expedients consists in heating
the feed water by the waste steam; and the feed water should in every case
be sent into the boiler _boiling hot_, instead of being quite cold, as is
at present generally the case. The ports of the cylinders should be as
large as possible; the expansion of the steam should be carried to a
greater extent; and in the case of engines with outside cylinders, the
waste steam should circulate entirely round the cylinders before escaping
by the blast pipe. The escape of heat from the boiler should be more
carefully prevented; and the engine should be balanced by weights on the
wheels to obviate a waste of power by yawing on the rails. The most
important expedient of all, however, lies in the establishment of a system
of registering the performance of all new engines, in order that
competition may stimulate the different constructors to the attainment of
the utmost possible economy; and under the stimulus of comparison and
notoriety, a large measure of improvement would speedily ensue. The
benefits consequent on public competition are abundantly illustrated by the
rapid diminution of the consumption of fuel in the case of agricultural
engines, when this stimulus was presented.
CHAPTER XI
OF VARIOUS FORMS, APPLICATIONS, AND APPLIANCES OF THE STEAM ENGINE.
In the English edition of this work, the first part of this chapter is
devoted to examples of Portable and fixed Agricultural engines, of
different makers and styles of workmanship, but not in sufficient detail,
nor illustrated on large enough scale to be of practical value as models,
forming rather in fact an illustrated catalogue of the manufacturer, than a
study for the mechanic. On this account, they have been entirely omitted,
and their place supplied by a few illustrations from American workmanship,
not only of Steam Engines, of various forms and applications, but also of
various machines, or appliances, connected with the working of engines, as
for the determination, or regulation of pressure, of the boilers; for the
supply or feed of the boilers, the regulation of the speed of the engine,
and the like.
The Gauges used in this country to show the pressures of steam in boilers
are of various constructions, but perhaps the most common is the Bourdon,
or, as it is known here, the Ashcroft gauge, from the party introducing it,
and holding the patent. Fig. 59 represents its interior construction. It
consists of a thin metallic tube, _a_, bent into nearly a complete circle
closed at one end, the steam being introduced at the other, at _b_. The
effect of the pressure of the steam on the interior of the tube is to
expand the circle, more or less according to the pressure, the elasticity
of the metal returning the circle to its original position, when the
pressure is removed. The free or closed end of the tube is connected by a
link _c_ with a lever _d_, at the opposite end of which is segmental gear,
in gear with a pinion, on which is a hand, which marks the pressure on a
dial. The dial and hand are not shown on the cut, but are on the exterior
case removed to show the construction.
[Illustration: Fig. 59.]
[Illustration: Fig. 60.]
Fig. 60 is an elevation of a boiler with Clark's Patent Steam and Fire
Regulator attached, for the control of the draft of the chimney by the
pressure of steam in the boiler. It consists of a chamber, _a_, with a
flexible diaphragm or cover on top, in communication with the boiler. On
this diaphragm rests a plunger or piston, which is held down like a safety
valve, by a lever and weight, _b_. The end of the lever is connected with a
balanced damper, _c_, in the chimney. The weight, _b_, is placed at any
required position on the lever, and when the pressure of steam in the
boiler, exerted on the diaphragm, becomes sufficient to raise the weight,
the lever rises, and the damper begins to close, and to check the draft in
the chimney. When properly adjusted, the machine works on a variation of
from, one to two pounds between the extremes of motion. When the dampers
are very large, say 3 feet or over, they should be set on rollers, like
common grindstone rollers; the regulator should be attached directly to the
damper, the length of the pipe connecting the regulator with the boiler
being of no account.
[Illustration: Fig. 61.]
Porter's Patent Governor, fig. 61, is a modification of the ordinary
centrifugal governor. Very small balls are employed, from 2-1/4 to 2-5/8
inches in diameter. These swing from a single joint at the axis of the
spindle, which is the most sensitive arrangement, and make from 300 to 350
revolutions per minute, at which speed their centrifugal force lifts the
counterpoise. The lower arms are jointed to the upper ones at the centres
of the balls, and connect with the slide by joints about two inches apart.
The counterpoise may be attached to the slide in any manner; for the sake
of elegance, it is put in the form of a vase rising between the arms, its
stem forming the slide. The vase is hollow and filled with lead, and weighs
from 60 lbs. to 175 lbs. It moves freely on the spindle, through nearly
twice the vertical distances traversed by the balls, and is capable of
rising from 2-1/2 to 3 inches, before its rim will touch the arms. It is
represented in the figure as lifted through about one half of its range of
action.
The standard is bored out of the solid, forming a long and perfect bearing
for the spindle; the arms and balls are of gun metal, the joint pins of
steel; every part of the governor is finished bright, except the bracket
carrying the lever, and the square base of the standard, which are painted.
The pulley is from 3 to 10 inches in diameter, and makes in the larger
sizes about 125 revolutions, and in the smaller 230 revolutions per minute;
the higher speed of the governor being got up by gearing.
Mr. Porter warrants the following action in this governor, operating any
regulating valve or cut-off which is in reasonably good order. The engine
should be run with the stop-valve wide open, and, except the usual oiling,
will require no attention from the engineer, under any circumstances, after
it is started, until it is to be stopped. No increase in the pressure of
steam will affect its motion perceptibly. The extreme possible variation in
the speed, between that at which the regulating valve will be held wide
open, and that at which it will be closed, is from 3 to 5 per cent., being
least in the largest governors. This is less than 1/6 of the variation
required by the average of ordinary governors, and is with difficulty
detected by the senses. The entire load which the engine is capable of
driving may be thrown on or off at once, and one watching the revolutions
cannot tell when it is done. The governor will be sensibly affected by a
variation in the motion of the engine of 1 revolution in 800.
Notwithstanding this extreme sensitiveness, or rather by reason of it, it
will not oscillate, but when the load is uniform will stand quite, or
nearly, motionless.
For the supply of the water to the boiler, in many positions, it is very
convenient to have a pump unconnected with the engine. On this account it
is very usual in this country to have what are called donkey pumps or
engines independent of the main engines, which can be used to feed the
boilers, or for supplying water for many other purposes.
Fig. 62 is a longitudinal section of the Worthington Steam Pump, the first
of its kind, and for many years in successful operation.
The general arrangement is that of a Steam Cylinder, the piston rod of
which, carried through into the water cylinder and attached directly to the
water plunger, works back and forth without rotary motion, and of course
without using either crank or fly wheel.
[Illustration: Fig. 62.]
In the figures, _a_ is the Steam Cylinder--_b_, the Steam Chest--_d_, a
handle for regulating the steam valve--_f_, the starting bar _g, g_,
tappets attached to the valve rod, which is moved by the contact of the arm
_e_, on the piston rod with said tappets--_h_, the double-acting water
plunger working through a packing ring--_o, o_, force valves--_o', o'_,
suction valves. The pump piston is represented as moving from right to
left, the arrows indicating the course of the water through the passages.
The suction valves _o'_, on the right side, and the force valves _o_, on
the left side, are show open; _x_, is an air chamber made of copper; _s_,
the suction pipe terminating in a vacuum chamber; made by prolonging the
suction pipe, and closing it perfectly tight at the top, the connection
being made to the pump by a branch as shown; _m, m_, are hand-hole plates,
affording easy access to the water valves; _n, n_, small holes through the
plunger, which relieve the pressure near the end of the stroke, to give
momentum to throw the valves when working at slow speed.
[Illustration: Fig. 63.]
Fig. 63 is a perspective view of H.R. Worthington's Duplex Steam Pump. The
prominent peculiarity of this pump is its valve motion. As seen in the cut,
two steam pumps are placed side by side (or end to end, if desired). Each
pump, by a rock shaft connected with its piston rod, gives a constant and
easy motion to the steam valve of the other. Each pump therefore gives
steam to and starts its neighbor, and then finishes its own stroke, pausing
an instant till its own steam valve, being opened by the other pump, allows
it to make the return stroke.
This combined action produces a perfectly positive valve motion without
dead points, great regularity and ease of motion, and entire absence of
noise or shock of any kind. Both kinds of pumps are made by Mr.
Worthington, of various size according to the requirements, the duplex
being used for boiler feed and for the supply of cities with water.
Fig. 64 is a side elevation of the Woodward Steam Pump. The pump is direct
acting. The steam and water piston being on the same rod, but momentum is
obtained to throw the valves by means of a fly wheel, placed beyond the
pump, and connected with the piston rod by a cross head and a yoke. The
machine is simple in its construction and action, and is extensively used.
Giffard's Injector, both in Europe and this country, is quite extensively
used to supply the place of a pump, as independent feed for all classes of
boilers. It is represented in elevation and section, figs. 65 and 66.
[Illustration: Fig. 64.]
[Illustration: Fig. 65.]
[Illustration: Fig. 66.]
_A_, steam pipe leading from the boiler. _B_, a perforated tube or
cylinder, through which the steam passes into the space _b_. _C_ screwed
rod for regulating the passage of steam through the annular conical space
_c_, and worked by the handle _d/_. _E_, suction pipe, leading from the
tank or hot well to small chamber _m_. _F_, annular conical opening or
discharge pipe, the size of which is regulated by the movement of the tube
or cylinder _B_. _G_, hand wheel for actuating the cylinder _B_. _H_,
opening, in connection with the atmosphere, intervening between discharge
pipe _F_ and the receiving pipe through which the water is forced. _I_,
tube through which the water passes to the boiler. _K_, valve for
preventing the return of the water from the boiler when the injector is not
working. _L_, waste or overflow pipe. _M_, nut to tighten the packing rings
_g_ and upper packing _i_ in cylinder _B_. _N_, lock nut to hold _M_.
The pipe _A_ is connected with the steam space of the boiler at its highest
part, to obtain as dry steam as possible. The passage of the steam into _A_
is controlled by a cock, as is also the feed pipe to the boiler. In
working, both are opened, the steam passes through _A_ into the space _b_,
and issuing through the nozzle _c_ with the pressure due to its head, and a
partial vacuum by its contact with the feed water, it drives this water in
connection with the jet through the pipe _F_ into the pipe _I_ in
connection with the water space of the boiler.
_Method of Working._--Turn the wheel so as to permit a small quantity of
water to flow to the instrument. Open the steam cock connecting the
apparatus with the boiler. Turn slightly the handle, which will admit a
small quantity of steam to the apparatus; a partial vacuum is thus
produced, causing the water to enter through the supply pipe. As soon as
this happens, which can be observed at the overflow pipe, the supply of
steam or water may be increased as required, up to the capacity of the
instrument, regulating either by means of the wheel and handle, so as to
prevent any overflow. The quantity of water delivered into the boiler, may
be varied by means of the stop cocks on the steam and water pipes, without
altering the handles on the injector; a graduated cock on the water supply
pipe is very convenient for this purpose.
The machines are manufactured by Wm. Sellers & Co. Philadelphia.
As an example of Portable Steam Engines, of which there are large numbers
in this country of different manufacturers, we give the representation
(fig. 67) of one made by J.C. Hoadley, of Lawrence, Mass.
[Illustration: Fig. 67.]
In these machines, the rules and proportions of the locomotive engine are
adapted to the requirements of stationary power, for all purposes under
forty horse power. The leading ideas are: high velocity, high pressure,
good valve motion, large fire-box, numerous and short flues, and steam
blast. The characteristic features are: great strength of boiler, fully
adequate to bear with safety 200. lbs. pressure per sq. in., great
compactness and simplicity, large and adjustable wearing surfaces, and the
entire absence of all finish, or polish, for mere show.
The cylinder is placed over the centre of the boiler, at the fire-box end,
so that the strain due to the engine is central to the boiler (which serves
as bed plate); the starting valve is under the hand of the engineer when at
the fire door; and both ends of the crank shaft are available for driving
pulleys.
For the sake of compactness, the cylinders are set low, by means of a
depression in the boiler between the stands of the crank shaft, to admit of
the play of the crank and connecting rod. All the parts are attached to the
boiler, which is made of sufficient strength to bear all extra strain due
to the working of the engine.
They have feed water heater, force pumps, Jackson's governor and valve,
belt for governor, belt pulley, turned on the face, steam gauge;
everything, in short, necessary to the convenient working of a steam
engine. All engines are fired up and tried before they leave the shop, and
they are warranted tight, safe, and complete.
A strong and convenient running gear, so arranged as to be easily attached
and detached at pleasure, is furnished, if desired; forming, when separate,
a useful wagon.
[Illustration: Fig. 68.]
Fig. 68 is a compact vertical engine, as built by R. Hoe & Co., of this
city. It is intended to drive printing presses, but is adapted to any kind
of work, and is especially suited to such places as require economy of
space. Although the value of expansion has been called in question by some
of the engineers of the United States Navy, and under an appropriation from
Congress is now to be made the subject of experiment; yet, in almost all
the manufactories and workshops of the United States, no matter what the
form of steam engine, or the purposes to which it is applied, whether
stationary, locomotive, or marine, some form of cut-off, by which expansion
of the steam can be availed of, is considered indispensable. Many varieties
are in use, but those engines are most popular in which the cut-off is
applied directly to the valves on the cylinder, opening them quickly and
shutting off almost instantly, avoiding all wire drawing of the steam at
the ports, and regulating the speed of the engine promptly. Of this class
of engines, those manufactured by the Corliss Steam Engine Company, of
Providence, R.I., are perhaps the widest known, not only for their
extensive introduction, but also from having, by a long and successful
litigation, established the claims of the patentee, Mr. George H. Corliss.
[Illustration: Fig. 70.]
Fig. 70 is a section of the cylinder and valve chests of a horizontal
Corliss engine. _S_ is the steam connection, and _E_ the exhaust; there are
two distinct sets of valves, the steam _s, s'_, and the exhaust _e, e'_,
operated independently of each other. In their construction the valves may
be considered cylindrical plugs, of which portions near the ports are cut
away to admit the steam and reduce the bearing surface; the valves are
fitted on the lathe and the seats by boring. The motion given to the valves
is rocking, but it will be observed that the valves are not firmly
connected to the rocking shaft or cylinder; in the figure the valves are
shown shade lined, and the shaft or stem plain; in this way the valves are
not affected by the packing of the valve stem, but always rest upon the
face of the ports. In the figure the piston is just about to commence its
outstroke, the movement of the steam is supposed to be represented by the
arrows; the inner steam valve _s_, and the outer exhaust _e'_, are just
beginning to open. It will be observed that the outer steam _s'_ is fully
closed, whilst the inner exhaust valve _e_ is but barely so, showing that
there has been a cut-off on the steam valve, but no lead to the exhaust,
that it was left fully open till the completion of the stroke.
[Illustration: Fig. 71.]
Fig. 71 is a side elevation of the cylinder, with the valve connections
with the governor. _S_ is the steam pipe; _s, s'_ handles to the steam
valves, and _e, e'_ to the exhaust valves, shown in dotted line in fig. 70.
The handles to the exhaust valves are connected directly to a rocking plate
_R_, to which motion is given by a connection _x_, with an eccentric on the
engine shaft. When once set, therefore the movement of the exhaust valves
is constant, and they will always be opened and closed at the same point of
the stroke. Connected with the rocking plate _R_, and on opposite sides of
its centre, the same as the exhaust valve connections, there are two
levers, vibrating on a centre _c_, of which one only is shown, as it covers
the other; to the upper ends of these levers pawls are attached, one end of
which rests on the stems or rods connected with the handles _s, s'_, of the
steam valves; on these stems there are notches against which the pawls
strike, and as the levers vibrate inward they push back the stems and
thereby open the valves, and this continues for the whole length of the
inward motion of the levers, or till the outer extremities of the pawls
come in contact with the end of the short lever _l_, which, pushing down
the outer end of the pawls, relieves the stems at the other ends, and the
valve stem returns to its place through the force of springs attached to
the outer extremities of the valve stems _a_, are cylindrical guides to the
valve stems, at the inner extremities of which are air cushions. The lever
_l_ is connected directly with the governor. As the balls rise, they
depress the extremity, which comes in contact with the pawls sooner, and
thereby shut the valves earlier; and on the contrary when the balls are
depressed, the valves remain open longer; as the pawls come in contact with
the stems always at one point, the steam valves open constantly, but are
closed at any point by the relief of the pawls, according to the speed of
the governor.
Fig. 71 represents, partly in section and partly in plan, the cylinder,
steam chests, valves, &c., of one of the Woodruff & Beach high pressure
Engines, Wright's patent.
Fig. 72 represents, in elevation, the cam shaft, to the upper end of which,
not shown in the drawing, is attached the ordinary centrifugal governor.
The cylinder, steam chests, valves, &c., being similar to those of other
engines, need no special notice; but the cam for opening and closing the
steam valves, fig. 72, requires particular attention, as it embodies a
beautiful and simple device for cutting off the steam with certainty at any
part of the stroke, the motion being produced automatically by the action
of the governor on this cam, throwing it more or less out of centre with
the spindle of the governor, as the rotation of the balls is less or more
rapid, the eccentricity of the cam determining the amount of steam admitted
to the working cylinder of the engine. To produce this effect the cam is
made as follows:
_C_ is a hollow cylinder or shell, with a part of one end formed into a cam
proper. Throughout the whole length of this piece, upon the inside, there
is a spiral groove cut to receive one end of a feather, by which its pitch
or eccentricity is regulated. _C'_ is also a hollow cylinder or shell, of
the same length and diameter as _C_, with a similar spiral groove cut on
the inside, the outside being perfectly smooth and plain, upon which the
toe (_t_) for closing the valves is fastened. The inside piece consists of
two hubs _D, D'_, eccentric with each other, and made in one piece, _D_
being turned to exactly fit the inside of the shell _C_, and _D'_ to fit
the shell _C'_, the hub _D'_ having a socket (_c_) into which the spindle
(_s_) of the governor is screwed; the end (_d_) of the hub _D_ forming a
journal or bearing, with a bevel wheel on its extremity to convey motion
from the crank-shaft gearing to the governor and cut-off. There is a hole
throughout the length of the inside hubs _D_ and _D'_, which is continued
through the spindle of the governor, and contains the rod (_r_) that
connects the cam with the governor. This hole is eccentric to the outside
surface of the hub _D_, as well as to the shell _C_, and concentric with
the hub _D'_ and shell _C'_, and with the governor rod (_r_).
The shell _C_ and hub _D_, and shell _C'_ and hub _D'_, are connected
together by feathers; one piece of each feather is of a spiral form, and
the other a straight or rectangular piece, the two being connected together
by a stub on the rectangular piece, which fits into a hole or bearing in
the other or spiral piece, so that the latter can turn on the stub and
accommodate itself to the groove in which it has to work. The spiral part
of each feather works in the spiral groove on the inside of its
corresponding shell _C_ and _C'_ respectively, and the rectangular pieces
work in a straight groove cut in the hubs _D_ and _D'_, the inner parts of
the rectangular pieces being fastened to the governor rod (_r_), so that
the feathers are permanently connected with the governor.
The shell _C'_ revolves inside of two yokes (_y_) and (_y'_), one attached
to each steam-valve toe, (_a_) and (_a'_) respectively.
On the inside of each yoke, and opposite to its valve-toe, is a raised
piece, against which the closing piece (_t_) on the shell (_C'_) acts to
close the valves.
This shell (_C'_), as before noticed, has a spiral groove on its inside,
similar in all respects to that in the cam-shell (_C_); and being acted
upon in the same manner and through the same rod by the governor, it is
evident that the closing piece (_t_) on its outside will always hold the
same relation to the opening toe on the lower or cam-shell (_C_); and
whatever alteration is made in the one, a corresponding alteration takes
place in the other, thereby insuring the closing of the valves at the
proper time at every point of the variation of the cut-off.
When the several pieces above described are put together, the apparatus for
opening and closing the valves and producing the cut-off is complete, as
shown in fig. 72, and it operates as follows:
[Illustration: Fig. 71.]
[Illustration: Fig. 72.]
Motion is communicated by gearing from the crank-shaft to the bevel wheel
on the piece (_d_) on the end of the hub _D_, and is communicated to the
spindle of the governor, which is screwed into the socket on _D'_. As the
balls rise or fall, through change of centrifugal force due to the
variation in the speed of rotation, they raise or depress the governor-rod,
which passes through the spindle and the hubs _D'_ and _D_, and is attached
to the feathers, thereby raising or depressing the feathers, which, acting
on their respective spiral grooves, instantly alters the lift of the cam on
the shell (_C_), and brings the closing toe (_t_) on the shell (_C'_) into
proper position for closing, and so regulates the amount of steam admitted
to the cylinder.
[Illustration: Fig. 71.]
Consequently, any speed may be selected at which the load of the engine is
to move, and any variation from that will be instantly felt by the
governor, and corrected by this simple and beautiful device. There is no
jar in the working of the parts; the feathers move noiselessly in their
grooves; the governor rod moves up and down through the spindle and the
hubs _D_ and _D'_, and can be regulated by hand to give any required
opening of the steam ports to suit the work to be done. Any change in the
amount of work will then alter the speed of the engine, and so affect the
governor and cam, as before said.
It is unnecessary to insist on the great economy attained by using steam
with a well-regulated cut-off, for practical men know now that the
essential points of excellence in the steam engine are a good boiler, which
generates the greatest quantity of steam for the least consumption of fuel;
and, secondly, a reliable cut-off, which uses the steam to the best
advantage, by admitting the proper quantity for the work required.
STEAM FIRE ENGINES.--Portable engines for the extinguishment of fires, are
an American invention, and to Messrs. A.B. & E. Latta, of Cincinnati,
working on the right principles, is due the credit which they claim in
their circular, as follows:
"We claim to be the _original_ and first _projectors_ of the _first
successful steam fire engine_ in the world's history. There have been many
attempts at making a machine of such construction as would answer to
extinguish fires; but none of them proved to be available in a sufficiently
short space of time to warrant their use as a fire apparatus. We hold that
a steam fire engine should be of such nature as to be brought into
requisition in as short a space of time as is necessary to get the machine
on the ground, and the hose laid and ready to work: that is, supposing the
fire to be within one square of the place where the steamer is located. The
object in locating a machine at any point is to protect that immediate
vicinity; and it is therefore absolutely necessary to have it available in
the shortest space of time, and that with unerring certainty. We think that
reliability is of the greatest importance to the protection of a city from
fire, as everything is dependent on the _working_ of such apparatus in
time; and for this reason no expense should be spared on this kind of
machinery."
Fig. 73 is a representation of one of the Messrs. Latta's fire engines, of
which there are many of different classes, according to the requirements;
they say that they can furnish engines as low as $1,000, and have made some
for $10,000.
The first peculiar feature of this engine is the boiler; it differs
entirely from all boilers now in use.
[Illustration: Fig. 73.]
The fire box or furnace is simply a square box or furnace of any required
dimensions; it is nothing more than a water space surrounding the fire,
stay-bolted as all water spaces are. It is made of boiler plate in the
usual manner. The water space extends only 2/3 of the height, the balance
being a single sheet. The bottom of this fire box is crossed by grate bars
to support the fuel; in its rear side are fire doors, inserted for firing.
The internal arrangements of the boiler are composed of a large number of
tubes, lying across in a horizontal position, put together in sections with
return bends resembling the coils for heating buildings. These coils are of
small pipe (say one inch in diameter), and as numerous as may be necessary.
They give the required amount of steam. They are secured to wrought-iron
plates at each end by rivets. These plates lie close to the box, and are
secured to it, top and bottom. These tubes are wrought iron, firmly screwed
into the bends, so as to prevent any possible breaking.
The box has a hole through both sheets, in the same manner as a hollow
stay-bolt, through which the coil pipe passes, having no connection with
the box. After passing into the box it divides into two pipes, then
subdivides into four, and so on, until its numbers equal the number of
coils in the box, and to which each limb is attached. The upper ends of
these coils are the same in number, and are carried through at the top or
nearly the top of the box. They then run down outside to the steam chamber,
or rather water space, as the box is both steam chamber and water space.
These pipes empty their contents into the box, steam and water, as it may
come, all together. It will be observed that these coils of tube are
sufficiently separated to allow the fire to pass between them freely, and
cover their whole surface.
The mode of operation of this boiler is this: The fire box is filled 2/3
full of water. The coils are dry at starting; the space for fuel being
filled with good wood, the fire is lighted, and in a few moments the
engineer moves his hand pump, which takes its water from the box to which
it is attached, and forces it through the coils. By this means steam is
generated in from 3 to 5 minutes, so as to start the engine.
It will be seen that the water performs a complete circuit; it is taken
from the box and passed through the coils; what is steam remains in the
steam chamber, and what is not (if any) drops back into the box from where
it started. Hence it will be seen that a large surface is exposed to a
small quantity of water, and in a way that it is entirely controllable. All
the engineer has to do to surcharge his steam, is to reduce the speed of
the pump (which is independent of the main engine). By raising the heat and
quantity of water, any degree of elasticity can be given to the steam, and
that, too, with the least amount of waste heat in giving a natural draft.
Hence the great economy of this boiler.
The next feature of this engine is, it has no wood work about it to perish
with the heat and roughness of the streets. All the wheels are wrought
iron; and, as yet, these are the only ones that have stood a steam fire
engine. The frame is wrought iron; truck, on which the front wheel is hung,
wrought iron. The axles are cast steel. The engine and pump is a
double-acting piston pump direct, without any rotary motion; with a
perfect balance valve, it is balanced at all times, and hence the engine
remains quiet without blocking, when at work. The engine is mounted on
three wheels, which enables it to be turned in a very short space.
Many engines have been constructed by the Messrs. Latta for the fire
companies, of different cities, and have been in successful competition
with other engines; the farthest throw ever made by one of their
first-class engines was 310 feet from a 1-5/8 inch nozzle; steaming time,
starting from cold water, 3-1/2 minutes.
[Illustration: Fig. 74 AMOSKEAG STEAM FIRE ENGINE.]
Fig. 74 is a representation of one class of steam fire engine, as built by
the Amoskeag Manufacturing Company, at Manchester, N.H. The boiler is an
upright tubular boiler, of a peculiar construction, the patent right to
which is vested in the Amoskeag Manufacturing Company. This boiler is very
simple in its combination, and for safety, strength, durability, and
capacity for generating steam is unsurpassed. No fan or artificial blower
is ever used or needed, the natural draft of the boiler being always
sufficient. Starting with cold water in the boiler, a working head of steam
can be generated in _less than five minutes_ from the time of kindling the
fire. The engine "Amoskeag," owned by the city of Manchester, has played
two streams in _three minutes and forty seconds_ after touching the match,
at the same time drawing her own water. The boilers are made and proved so
as to be safely run at a steam pressure of 140 to 150 lbs. to the square
inch; but the engines are constructed so as to give the best streams at a
pressure of about 100 lbs. to the square inch, and for service at fires a
steam pressure of about 60 lbs. to the square inch is all that is required.
The various styles of engine are all _vertical_ in their action, and in all
the pumps and steam cylinders are firmly and directly fastened to the
boiler, the steam cylinders being attached directly to the steam dome. This
arrangement obviates the necessity of carrying steam to the cylinders
through pipes of considerable length, and the machine has very little
vibratory motion when in operation--so little that it is not necessary to
block its wheels to keep it in its place, or to take the weight off the
springs before commencing work.
The pumps are placed on the engines as near the ground as they can be with
safety, and are arranged so as to attach the suction and leading hose to
either or both sides of the machine, as may be most convenient or
desirable, so that less difficulty will be found in placing an engine for
work, and when required to draw its own water, it has only to draw it the
shortest possible distance.
Each engine has two "feed pumps" for supplying the boiler, and also a
connection between the main forcing pumps and the boiler, so that it can be
supplied from that source if desirable. The tank which carries the water
for supplying the boiler is so placed that the water in it is always above
the "feed pumps," an advantage that insures the almost certain working of
these pumps. These pumps are of brass, the best locomotive pattern, and one
of them running with the engine, when at work, furnishes an ample supply of
water to the boiler.
[Illustration: Fig. 75.]
The engines are exceedingly portable; they can be turned about or placed
for service in as contracted a space as any hand engine, and two good
horses will draw a first-class engine with the greatest ease, carrying at
the same time water for the boiler, a supply of fuel sufficient to run the
engine two hours, the driver, the engineer, and the fireman.
Fig. 75 is a representation of the class of steam fire engine built by
Silsbee, Mynderse & Co., Seneca Falls, N. Y. under Holly's patent.
The boiler is vertical, with vertical water tubes passing directly through
the fire. These tubes are closed at the bottom and open at the top, where
they pass through a water-tight plate, and communicate with the water in
the boiler. The arrangement of the tubes causes a constant current, the
water rising on the outside of the tubes as they are heated, and its place
being supplied by a current flowing downward through the tube to the
boiler. The smoke and flame pass among the tubes up through flues.
Both engine and pump are rotary, and of the same type. They consist
essentially of two elliptical rotary pistons, cogged and working into one
another in an air-tight case. The pistons fit close to the inside of the
case, and gear into each on the line of their conjugate diameters. The
action is somewhat similar to the old-fashioned rotary pump, consisting of
two cog wheels in gear with, each other, the spaces at the side of the case
being filled with water, which at the centre are occupied by the teeth in
gear. In Holly's pump, instead of uniform teeth, and depending on the fit
of the teeth with the side of the case and with each other for the packing,
there are two large teeth in each piston opposite each other, which have
slide pistons, and intermediate with these large teeth are small cogs,
which continue the motion of the rotary pistons. The machine works very
smoothly, and performs the work necessary, in ordinary service, under a
pressure of 50 to 60 lbs.
There are many other makers of fire engines in this country; but sufficient
examples are given to illustrate the class; so successful have they been,
that they are fast superseding hand engines, even in the smaller cities.
Under a paid department, the following is, in the city of Boston, Mass.,
the comparative cost of running the two kinds of engines, viz.:
STEAM FIRE ENGINE.
1 engineer........................................... $720 00
1 fireman............................................ 600 00
1 driver............................................. 600 00
1 foreman of hose.................................... 150 00
8 hosemen, at $125 each.............................. 375 00
-- --------
7 men................................................ $2,445 00
Keeping of 2 horses.................................. 315 00
--------
Total......................................... $2,760 00
HAND ENGINE.
1 foreman............................................ $150 00
1 assistant foreman.................................. 125 00
1 clerk.............................................. 125 00
1 steward............................................ 125 00
3 leading hosemen, at $125 each...................... 375 00
33 men, at $100 each................................. 3,300 00
-- ---------
40 men............................................... $4,200 00
Here the engineer, fireman, and driver are constantly employed, the hosemen
have other employment in the neighborhood, but all the company sleep in the
engine house.
In the city of Manchester, N.H., a steam fire engine company is composed of
fourteen men, all told, one of whom, acting as driver and steward, is
constantly employed, remaining at the engine house with a pair of horses
always ready to run out with the engine in case of an alarm of fire. The
other members of the company have other employments, and turn out only on
an alarm of fire.
STEAM FIRE ENGINES.
"Amoskcag," Expenditures..................... $864 32
"Fire King," " ..................... 855 78
"E.W. Harrington," " ..................... 496 09
The above expense includes pay of members, team expenses, cost of gas,
wood, coal, and all necessities incident to service. The "E.W. Harrington"
is a second-class engine, stationed in the outskirts of the city, and was
run cheaper from the fact that no horses were kept for it by the city.
A first-class hand-engine company is allowed to number, all told, fifty
men, and the members of the company are paid as follows:
FIRST-CLASS HAND-ENGINE COMPANY.
1 foreman.......................................... $35 00
1 assistant foreman............................... 28 00
1 clerk........................................... 28 00
1 steward........................................ 68 00
46 men, at $18 each................................ 828 00
--------
50 men. Total.............................. $987 00
By this it will be seen, that in a city like Manchester, with from twenty
to twenty-five thousand inhabitants, a first-class steam fire engine can be
run at an expense not to exceed that of a first-class hand engine, while in
service it will do at least _four times_ the work. The cost of repairs is
found by experience to be no greater on the steam fire engines than on hand
engines.
The Excavator, fig. 76, is the invention of the late Mr. Otis, an
application of the spoon dredging machine of the docks to railway purposes,
with very important modifications. The machine consists of a strong truck,
_A_, _A_, mounted on railway wheels, on which is placed the boiler _C_, the
crane _E_, and the requisite gearing. The excavator or shovel, _D_, is a
box of wrought iron, with strong points in front to act as picks in
loosening the earth, and its bottom hung by a hinge at _d_, so that, by
detaching a catch, it may fly open and discharge the material raised. To
operate the machine, suppose the shovel _D_ to be in the position shown in
the cut; it is lowered by the chains _o_, _o_, and thrown forward or
backward, if necessary, by the drum _B_, and handle _S_, till the picks in
the front of the shovel are brought in proper contact with the face of the
cut; motion forward is now given to the shovel by the drum _B_ and handle
_S_, and at the same time it is raised by the chains _o_, _o_. These two
motions can be so adjusted to each other, as to give movement to the shovel
to enable it to loosen and scrape up a shovelful of earth. The handle _S_
is now left free, and the shovel _D_ is raised vertically by the chains
_o_, _o_. The crane is now turned round, till the shovel comes over a rail
car on a side track; the bottom of the shovel is opened, and the dirt
deposited in the car. All these motions are performed by the aid of a steam
engine, and are controlled by a man who stands on a platform at _f_.
[Illustration: Fig 76.]
692. _Q._--Having now described the most usual and approved forms of
engines applicable to numerous miscellaneous purposes for which a moderate
amount of steam power is required, will you briefly recapitulate what
amount of work of different kinds an engine of a given power will perform,
so that any one desiring to employ an engine to perform a given amount of
work, will be able to tell what the power of such engine should be?
_A._--It will of course be impossible to recapitulate all the purposes to
which engines are applicable, or to specify for every case the amount of
power necessary for the accomplishment of a given amount of work; but some
examples may be given which will be applicable to the bulk of the cases
occurring in practice.
693. _Q._--Beginning, then, with the power necessary for threshing,--a 4
horse power engine, with cylinder 6 inches diameter, pressure of steam 45
lbs., per square inch, and making 140 revolutions per minute, will thresh
out 40 quarters of wheat in 10 hours with a consumption of 3 cwt. of coals.
_A._--Although this may be done, it is probably too much to say that it can
be done on an average, and about three fourths of a quarter of wheat per
horse power would probably be a nearer average. The amount of power
consumed varies with the yield.
Messrs. Barrett, Exall, and Andrewes give the following table as
illustrative of the work done, and the fuel consumed by their portable
engines; but this must be regarded as a maximum performance:--
Number of | Weight of | Quarters of | Quantity of | Quantity of
Horse Power.| Engine. | Corn thrashed| Coals consumed| Water required
| | in 10 Hours. | in 10 Hours. | for 10 Hours
| | | | in Gallons.
------------|-----------|--------------|---------------|---------------
|Tons. Cwts.| | Cwts. |
4 | 2 0 | 40 | 3 | 360
5 | 2 5 | 50 | 4 | 380
6 | 2 10 | 60 | 5 | 460
7 | 2 15 | 70 | 6 | 540
8 | 3 0 | 80 | 7 | 620
10 | 3 10 | 100 | 9 | 780
-----------------------------------------------------------------------
694. _Q._--In speaking of horses power, I suppose you mean indicator horse
power?
_A._--Yes; or rather the dynamometer horse power, which is the same,
barring the friction of the engine. At the shows of the Royal Agricultural
Society, the power actually exerted by the different engines is ascertained
by the application of a friction wheel or dynamometer.
695. _Q._--Can you give any other examples of the power necessary for
grinding corn?
_A._--An engine exerting 23-1/3 horses power by the indicator works two
pairs of flour stones of 4 feet 8 inches diameter, two pairs of stones
grinding oatmeal of 4 feet 8 inches diameter, one dressing machine, one
pair of fanners, one dust screen, and one sifting machine. One of the flour
stones makes 85, and the other 90 revolutions in the minute. One of the
oatmeal stones makes 120, and the other 140 revolutions in the minute. To
take another case:--An engine exerting 26-1/2 indicator horses power works
two pairs of flour stones, one dressing machine, two pairs of stones
grinding oatmeal, and one pair of shelling stones. The flour stones, one
pair of the oatmeal stones, and shelling stones, are 4 feet 8 inches
diameter. The diameter of the other pair of oatmeal stones is 3 feet 8
inches. The length of the cylinder of the dressing machine is 7 feet 6
inches. The flour stones make 87 revolutions in the minute, and the larger
oatmeal stone 111 revolutions, but the smaller oatmeal stone and the
shelling stone revolve faster than this. At the time the indicator diagram
was taken, each pair of flour stones was grinding at the rate of 5 bushels
an hour; each pair of oatmeal stones about 24 bushels an hour; and the
shelling stones were shelling at the rate of about 54 bushels an hour. The
fanners and screen were also in operation.
696. _Q._--Have you any other case to enumerate?
_A._--I may mention one in which the power of the same engine was increased
by giving it a larger supply of steam. The engine when working with 8.65
horses power, gives motion to one pair of oatmeal stones of 4 feet 6 inches
diameter, and one pair of flour stones 4 feet 8 inches diameter. The
oatmeal stone makes 100 revolutions in the minute, and the flour stone 89.
The oatmeal stones grind about 36 bushels in the hour, and the flour stones
5 bushels in the hour. The engine when working to 12 horses power drives
one pair of flour stones, 4 feet 8 inches diameter, at 89 revolutions per
minute and one pair of stones of the same diameter at 105 revolutions,
grinding beans for cattle. The flour mill stones with this proportion of
power, being more largely fed, ground 6 bushels per hour, and the other
stones also ground 6 bushels per hour. When the power was increased to 18
horses, and the engine was burdened in addition with a dressing machine
having a cylinder of 19 inches diameter, the speed of the flour stone fell
to 85, and of the beans stone to 100 revolutions per minute, and the yield
was also reduced. The dressing machine dressed 24 bushels per hour.
697. _Q._--What is the power necessary to work a sugar mill such as is used
to press the juice from canes in the West Indies?
_A._--Twenty horses power will work a sugar mill having rollers about 5
feet long and 28 inches diameter; the rollers making 2-1/3 turns in a
minute. If the rollers be 26 inches diameter and 4-1/2 feet long, 18 horses
power will suffice to work them at the same speed, and 16 horses power if
the length be reduced to 3 feet 8 inches. 12 horses power will be required
to work a sugar mill with rollers 24 inches diameter and 4 feet 2 inches
long; and 10 horses power will suffice if the rollers be 3 feet 10 inches
long and 23 inches diameter. The speed of the surface of sugar mill rollers
should not be greater than 16 feet per minute, to allow time for the canes
to part with their juice. In the old mills the speed was invariably too
great. The quantity of juice expressed will not be increased by increasing
the speed of the rollers, but more of the juice will pass away in the
begass or woody refuse of the cane.
698. _Q._--What is the amount of power necessary to drive cotton mills?
_A._--An indicator or actual horse power will drive 305 hand mule spindles,
with proportion of preparing machinery for the same; or 230 self-acting
mule spindles with preparation; or 104 throstle spindles with preparation;
or 10-1/2 power looms with common sizing. The throstles referred to are the
common throstles spinning 34's twist for power loom weaving, and the
spindles make 4000 turns per minute. The self-acting mules are Robert's,
about one half spinning 36's weft, and spindles revolving 4800 turns per
minute; and the other half spinning 36's twist, with the spindles revolving
5200 times per minute. Half the hand mules were spinning 36's weft, at 4700
revolutions, and the other half 36's twist at 5000 revolutions per minute.
The average breadth of the looms was 37 inches, weaving 37 inch cloth,
making 123 picks per minute,--all common calicoes about 60 reed, Stockport
count, and 68 picks to the inch. To take another example in the case of a
mill for twisting cotton yarn into thread:--In this mill there are 27
frames with 96 common throstle spindles in each, making in all 2592
spindles. The spindles turn 2200 times in a minute; the bobbins are 1-7/8
inches diameter, and the part which holds the thread is 2-3/16 inches long.
In addition to the twisting frames the steam engine works 4 turning lathes,
3 polishing lathes, 2 American machines for turning small bobbins, two
circular saws, one of 22 and the other of 14 inches diameter, and 24 bobbin
heads or machines for filling the bobbins with finished thread. The power
required to drive the whole of this machinery is 28-1/2 horses. When all
the machinery except the spindles is thrown off, the power required is 21
horses, so that 2592, the total number of spindles, divided by 21, the
total power, is the number of twisting spindles worked by each actual horse
power. The number is 122.84.
699. _Q._--What work will be done by a given engine in sawing timber,
pressing cotton, blowing furnaces, driving piles, and dredging earth out of
rivers?
_A._--A high pressure cylinder 10 inches diameter, 4 feet stroke, making 35
revolutions with steam of 90 to 100 lbs. on the square inch, supplied by
three cylindrical boilers 30 inches diameter and 20 feet long, works two
vertical saws of 34 inches stroke, which are capable of cutting 30 feet of
yellow pine, 18 inches deep, in the minute. A high pressure cylinder 14
inches diameter and 4 feet stroke, making 60 strokes per minute with steam
of 40 lbs. on the square inch, supplied by three cylindrical boilers
without flues, 30 inches diameter and 26 feet long, with 32 square feet of
grate surface, works four cotton presses geared 6 to 1, with two screws in
each, of 7-1/2 inches diameter and 1-5/8 pitch, which presses will screw
1000 bales of cotton in the twelve hours. Also one high pressure cylinder
of 10 inches diameter and 3 feet stroke, making 45 to 60 revolutions per
minute, with steam of 45 to 50 lbs. per square inch, with two hydraulic
presses having 13 inch rams of 41 feet stroke, and force pumps 2 inches
diameter and 6 inches stroke, presses 30 bales of cotton per hour. One
condensing engine with cylinder 56 inches diameter, 10 feet stroke, and
making 15 strokes per minute with steam of 60 lbs. pressure per square
inch, cut off at 1/4th of the stroke, supplied by six boilers, each 5 feet
diameter, and 24 feet long, with a 22-inch double-return flue in each, and
198 square feet of fire grate, works a blast cylinder of 126 inches
diameter, and 10 feet stroke, at 15 strokes per minute. The pressure of the
blast is 4 to 5 lbs. per square inch; the area of pipes 2300 square inches,
and the engine blows four furnaces of 14 feet diameter, each making 100
tons of pig iron per week. Two high pressure cylinders, each of 6 inches
diameter and 18 inches stroke, making 60 to 80 strokes per minute, with
steam of 60 Lbs. per square inch, lift two rams, each weighing 1000 lbs.,
five times in a minute, the leaders for the lift being 24 feet long. One
high pressure cylinder of 12 inches diameter and 5 feet stroke, making 20
strokes per minute, with steam of 60 to 70 lbs. pressure per square inch,
lifts 6 buckets full of dredging per minute from a depth of 30 feet below
the water, or lifts 10 buckets full of mud per minute from a depth of 18
feet below the water.
CHAPTER XII.
MANUFACTURE AND MANAGEMENT OF STEAM ENGINES.
CONSTRUCTION OF ENGINES.
700. _Q._--What are the qualities which should be possessed by the iron of
which the cylinder of steam engines are made?
_A._--The general ambition in making cylinders is to make them sound and
hard; but it is expedient also to make them tough, so as to approach as
nearly as possible to the state of malleable iron. This may be done by
mixing in the furnace as many different kinds of iron as possible; and it
may be set down as a general rule in iron founding, that the greater the
number of the kinds of metal entering into the composition of any casting,
the denser and tougher it will be. The constituent atoms of the different
kinds of iron appear to be of different sizes, and the mixture of different
kinds maintains the toughness, while it adds to the density and cohesive
power. Hot blast iron was at one time generally believed to be weaker than
cold blast iron, but it is now questioned whether it is not the stronger of
the two. The cohesive strength of unmixed iron is not in proportion to its
specific gravity, and its elasticity and power to resist shocks appear to
become greater as the specific gravity becomes less. Nos. 3 and 4 are the
strongest irons. In most cases, iron melted in a cupola is not so strong as
when remelted in an air furnace, and when run into green sand it is not
reckoned so strong as when run into dry sand, or loam. The quality of the
fuel, and even the state of the weather, exerts an influence on the quality
of the iron: smelting furnaces, on the cold blast principle, have long been
known to yield better iron in winter than in summer, probably from the
existence of less moisture in the air; and it would probably be found to
accomplish an improvement in the quality of the iron if the blast were made
to pass through a vessel containing muriate of lime, by which the moisture
of the air would be extracted. The expense of such a preparation would not
be considerable, as, by subsequent evaporation, the salt might be used over
and over again for the same purpose.
701. _Q._--Will you explain the process of casting cylinders?
_A._--The mould into which the metal is poured is built up of bricks and
loam, the loam being clay and sand ground together in a mill, with the
addition of a little horse-dung to give it a fibrous structure and prevent
cracks. The loam board, by which the circle of the cylinder is to be swept,
is attached to an upright iron bar, at the distance of the radius of the
cylinder, and a cylindrical shell of brick is built up, which is plastered
on the inside with loam, and made quite smooth by traversing the
perpendicular loam board round it. A core is then formed in a similar
manner, but so much smaller as to leave a space between the shell and the
core equal to the thickness of the cylinder, and into this space the melted
metal is poured. Whatever nozzles or projections are required upon the
cylinder, must be formed by means of wooden patterns, which are built into
the shell, and subsequently withdrawn; but where a number of cylinders of
the same kind are required, it is advisable to make these patterns of iron,
which will not be liable to warp or twist while the loam is being dried.
Before the iron is cast into the mould, the interior of the mould must be
covered with finely powdered charcoal--or blackening, as it is technically
termed; and the secret of making finely skinned castings lies in using
plenty of blackening. In loam and dry sand castings the charcoal should be
mixed with thick clay water, and applied until it is an eighth of an inch
thick, or more; the surface should be then very carefully smoothed or
sleeked, and if the metal has been judiciously mixed, and the mould
thoroughly dried, the casting is sure to be a fine one. Dry sand and loam
castings should be, as much as possible, made in boxes; the moulds may
thereby be more rapidly and more effectually dried, and better castings
will be got with a less expense.
702. _Q._--Will you explain the next operation which a cylinder undergoes?
_A._--The next stage is the boring; and in boring cylinders of 74 inches
diameter, the boring bar must move so as to make one revolution in about
4-1/2 minutes, at which speed the cutters will move at the rate of about
5 feet per minute. In boring brass, the speed must be slower; the common
rate at which the tool moves in boring brass air pumps is about 3 feet per
minute. If this speed be materially exceeded the tool will be spoiled, and
the pump made taper. The speed proper for boring a cylinder will answer for
boring the brass air pump of the same engine. A brass air pump of 36-1/2
inches diameter requires the bar to make one turn in about three minutes,
which is also the speed proper for a cylinder 60 inches in diameter. To
bore a brass air pump 36-1/2 inches in diameter requires a week, an iron
one requires 48 hours, and a copper one 24 hours. In turning a malleable
iron shaft 12-3/4 inches in diameter, the shaft should make about five
turns per minute, which is equivalent to a speed in the tool of about 16
feet per minute; but this speed may be exceeded if soap and water be
plentifully run on the point of the tool. A boring mill, of which the speed
may be varied from one turn in six minutes to twenty-five turns in one
minute, will be suitable for all ordinary wants that can occur in practice.
703. _Q._--Are there any precautions necessary to be observed in order that
the boring may be truly effected?
_A._--In fixing a cylinder into the boring mill, great care must be taken
that it is not screwed down unequally; and indeed it will be impossible to
bore a large cylinder in a horizontal mill without being oval, unless the
cylinder be carefully gauged when standing on end, and be set up by screws
when laid in the mill until it again assumes its original form. A large
cylinder will inevitably become oval if laid upon its side; and if while
under the tension due to its own weight it be bored round, it will become
oval again when set upon end. If the bottom be cast in, the cylinder will
be probably found to be round at one end and oval at the other, unless a
vertical boring mill be employed, or the precautions here suggested be
adopted.
704. _Q._--Does the boring tool make the cylinder sufficiently smooth for
the reception of the piston?
_A._--Many engine makers give no other finish to their cylinders; but
Messrs. Penn grind their cylinders after they are bored, by laying them on
their side, and rubbing a piece of lead, with a cross iron handle like that
of a rolling stone, and smeared with emery and oil, backward and forward--
the cylinder being gradually turned round so as to subject every part
successively to the operation. The lead by which this grinding is
accomplished is cast in the Cylinder, whereby it is formed of the right
curve; but the part of the cylinder in which it is cast should be
previously heated by a hot iron, else the metal may be cracked by the
sudden heat.
705. _Q._--How are the parts of a piston fitted together so as to be
perfectly steam tight?
_A._--The old practice was to depend chiefly upon grinding as the means of
making the rings tight upon the piston or upon one another; but scraping is
now chiefly relied on. Some makers, however, finish their steam surfaces by
grinding them with powdered Turkey stone and oil. A slight grinding, or
polishing, with powdered Turkey stone and oil, appears to be expedient in
ordinary cases, and may be conveniently accomplished by setting the piston
on a revolving table, and holding the ring stationary by a cross piece of
wood while the table turns round. Pieces of wood may be interposed between
the ring and the body of the piston, to keep the ring nearly in its right
position; but these pieces of wood should be fitted so loosely as to give
some side play, else the disposition would arise to wear the flange of the
piston into a groove.
706. _Q._--What kind of tool is used for finishing surfaces by scraping?
_A._--A flat file bent, and sharpened at the end, makes an eligible scraper
for the first stages; or a flat file sharpened at the end and used like a
chisel for wood. A three-cornered file, sharpened at all the corners, is
the best instrument for finishing the operation. The scraping tool should
be of the best steel, and should be carefully sharpened at short intervals
on a Turkey stone, so as to maintain a fine edge.
707. _Q._--Will you explain the method of fitting together the valve and
cylinder faces?
_A._--Both faces must first be planed, then filed according to the
indications of a metallic straight edge, and subsequently of a thick
metallic face plate, and finally scraped very carefully until the face
plate bears equally all over the surface. In planing any surface, the
catches which retain the surface on the planing machine should be relaxed
previously to the last cut, to obviate distortion from springing. To
ascertain, whether the face plate bears equally, smear it over with a
little red ochre and oil, and move the face plate slightly, which will fix
the color upon the prominent points. This operation is to be repeated
frequently; and as the work advances, the quantity of coloring matter is to
be diminished, until finally it is spread over the face plate in a thin
film, which only dims the brightness of the plate. The surfaces at this
stage must be rubbed firmly together to make the points of contact visible,
and the higher points will become slightly clouded, while the other parts
are left more or less in shade. If too small a quantity of coloring matter
be used at first, it will be difficult to form a just conception of the
general state of the surface, as the prominent points will alone be
indicated, whereas the use of a large quantity of coloring matter in the
latter stages would destroy the delicacy of the test the face plate
affords. The number of bearing points which it is desirable to establish on
the surface of the work, depends on the use to which the surface is to be
applied; but whether it is to be finished with great elaboration, or
otherwise, the bearing points should be distributed equally over the
surface. Face plates, or planometers, as they are sometimes termed, are
supplied by most of the makers of engineering tools. Every factory should
be abundantly supplied with them, and also with steel straight edges; and
there should be a master face plate, and a master straight edge, for the
sole purpose of testing, from time to time, the accuracy of those in use.
708. _Q._--Is the operation of surfacing, which you have described,
necessary in the case of all slide valves?
_A._--Yes; and in fitting the faces of a D valve, great care must, in
addition, be taken that the valve is not made conical; for unless the back
be exactly parallel with the face, it will be impossible to keep the
packing from being rapidly cut away. When the valve is laid upon the face
plate, the back must be made quite fair along the whole length, by draw
filing, according to the indications of a straight edge; and the distance
from the face to the extreme height of the back must be made identical at
each extremity.
709. _Q._--When you described the operation of boring the cylinder, you
stated that the cylinder, when laid upon its side, became oval; will not
this change of figure distort the cylinder face?
_A._--It is not only in the boring of the cylinder that it is necessary to
be careful that there is no change of figure, for it will be impossible to
face the valves truly in the case of large cylinders, unless the cylinder
be placed on end, or internal props be introduced to prevent the collapse
due to the cylinder's weight. It may be added, that the change of figure is
not instantaneous, but becomes greater after some continuance of the strain
than it was at first, so that in gauging a cylinder to ascertain the
difference of diameter when it is placed on its side, it should have lain
some days upon its side to ensure the accuracy of the operation.
710. _Q._--How is any flaw in the valve or cylinder face remedied?
_A._--Should a hole occur either in the valve, in the cylinder, or any
other part where the surface requires to be smooth, it may be plugged up
with a piece of cast iron, as nearly as possible of the same texture. Bore
out the faulty part, and afterward widen the hole with an eccentric drill,
so that it will be of the least diameter at the mouth. The hole may go more
than half through the iron: fit then a plug of cast iron roughly by filing,
and hammer it into the hole, whereby the plug will become riveted in it,
and its surface may then be filed smooth. Square pieces may be let in after
the same fashion, the hole being made dovetailed, and the pieces thus
fitted will never come out.
711. _Q._--When cylinders are faced with brass, how is the face attached to
the cylinder?
_A._--Brass faces are put upon valves or cylinders by means of small brass
screws tapped into the iron, with conical necks for the retention of the
brass: they are screwed by means of a square head, which, when the screw is
in its place, is cut off and filed smooth. In some cases the face is made
of extra thickness, and a rim not so thick runs round it, forming a step or
recess for the reception of brass rivets, the heads of which are clear of
the face.
712. _Q._--What is the best material for valve faces?
_A._--Much trouble is experienced with every modification of valve face;
but cast iron working upon cast iron is, perhaps, the best combination yet
introduced. A usual practice is to pin brass faces on the cylinder,
allowing the valve to retain its cast iron face. Some makers employ brass
valves, and others pin brass on the valves, leaving the cylinder with a
cast iron face. If brass valves are used, it is advisable to plane out two
grooves across the face, and to fill them up with hard cast iron to prevent
rutting. Speculum metal and steel have been tried for the cylinder faces,
but only with moderate success. In some cases the brass gets into ruts; but
the most prevalent affection is a degradation of the iron, owing to the
action of the steam, and the face assuming a granular appearance, something
like loaf sugar. This action shows itself only at particular spots, and
chiefly about the angles of the port or valve face. At first the action is
slow; but when once the steam has worked a passage for itself, the cutting
away becomes very rapid, and, in a short time, it will be impossible to
prevent the engine from heating when stopped, owing to the leakage of steam
through the valve into the condenser. Copper steam pipes seem to have some
galvanic action on valve faces, and malleable iron pipes have sometimes
been substituted; but they are speedily worn out by oxidation, and the
scales of rust which are carried on by the steam scratch the valves and
cylinders, so that the use of copper pipes is the least evil.
713. _Q._--Will you explain in what manner the joints of an engine are
made?
_A._--Rust joints are not now much used in engines of any kind, yet it is
necessary that the engineer should be acquainted with the manner of their
formation. One ounce of sal-ammoniac in powder is mingled with 18 ounces or
a pound of borings of cast iron, and a sufficiency of water is added to wet
the mixture thoroughly, which should be done some hours before it is wanted
for use. Some persons add about half an ounce of flowers of brimstone to
the above proportions, and a little sludge from the grindstone trough. This
cement is caulked into the joints with a caulking iron, about three
quarters of an inch wide and one quarter of an inch thick, and after the
caulking is finished the bolts of the joints may be tried to see if they
cannot be further tightened. The skin of the iron must, in all cases, be
broken where a rust joint is to be made; and, if the place be greasy, the
surface must be well rubbed over with nitric acid, and then washed with
water, till no grease remains. The oil about engines has a tendency to
damage rust joints by recovering the oxide. Coppersmiths staunch the edges
of their plates and rivets by means of a cement formed of pounded
quicklime, with serum of blood, or white of egg; and in copper boilers such
a substance may be useful in stopping the impalpable leaks which sometimes
occur, though Roman, cement appears to be nearly as effectual.
714. _Q._--Will you explain the method of case hardening the parts of
engines?