VALVES AND VALVE FITTINGS
In the use of steam, compressed gas, or any medium which must have a
controllable flow, valves are a necessary element; and the important
point is to know what is best adapted for the use which is required in
each case.
For this reason one of the best guides is to fully understand the
construction of each. The following illustrations and descriptions will
give a good idea of the various types in use.
[Illustration: _Fig. 72. Check Valve._]
Check Valve.--Fig. 72 shows a longitudinal section of a check valve,
which is designed to prevent the water from returning or backing up
from the pressure side. The cylindrical body A is threaded at each end,
and has an inclined partition B therein which has a circular aperture.
[Illustration: _Fig. 73. Gate Valve._]
The upper side of the shell has an opening, adapted to be closed by a
cap C, large enough to insert the valve D, which is hinged to the upper
side of the partition. Water or gas is forced in through the valve in
the direction of the arrow, and the hinged valve is always in position
to close the opening in the partition.
In case the valve should leak it may be readily ground by taking the
small plug E from the opening, and with a screw driver, turning the
valve, and thereby fit it snugly on its seat.
[Illustration: _Fig. 74. Globe Valve._]
Gate Valve.--The cylindrical shell A has its ends internally threaded,
and is provided, midway between its ends, with a partition wall B,
having a central aperture. The upper side of the shell has an opening to
receive the bonnet C, through which the valve stem D passes. This stem
carries at its lower end a gate E which rests against the partition B.
The stem D is threaded to screw into the threaded bore of the gate. A
packing gland F surrounds the stem D. It will thus be seen that the
turning of the stem D draws the gate up or down, and thus effects an
opening, which provides a direct passage for the water through the valve
body.
Globe Valve.--A globe valve has the advantage that the valve is forced
against its seat by the pressure of the wheel, differing from the gate
valve, that depends on the pressure of the fluid to keep it tight.
The valve body A has therein a Z-shaped partition B, the intermediate,
horizontally-disposed limb of the partition being directly below the
opening through the body, which is designed to receive the bonnet C.
The bonnet has a central vertical bore, the lower end of which is
threaded to receive the wheel spindle. The lower end of the spindle
carries the circular valve, which is seated in the opening of the
Z-shaped partition.
The Corliss Valve.--The valve itself is of the rotary type, as shown in
Fig. 75, in which the port A goes to the cylinder, and B is the passage
for the steam from the boiler. The cylindrical valve body C has within
the aperture B a gate D, one edge of which rests against the abutment
through which the port A is formed, and this gate has within it the bar
E which is connected with the crank outside of the casing.
The Corliss Valve-Operating Mechanism.--As the operation of the valves
in the Corliss type of engine is so radically different from the
ordinary reciprocation engine, a side view of the valve grouping and its
connecting mechanism are shown in Fig. 76.
[Illustration: _Fig. 75. Corliss Valve._]
The cylinder has an inlet valve A at each end, and an outlet valve B at
each end for the discharge of the steam. C is a valve rod from the
eccentric which operates the valves, and D a wrist plate, having an
oscillatory or rocking motion around its center E. The attachments F F,
of the steam rods, open the inlet ports A A, and G G, are the
attachments of exhaust rods which open and close the exhaust valves B B.
H H are catches which can be unhooked from the stems of the valves A by
the governor rods J J.
The vertical links K, K are connected at their lower ends with the
pistons of dash pots, and have their upper ends attached to the valve
spindles, and act to close the valves A A when the catches H are
released by the governor rods J by means of the weights of the pistons
in the dash pots.
[Illustration: _Fig. 76. Corliss Valve-operating Mechanism._]
The dash pots L L act in such a manner as to cushion the descent of the
links K and thus prevent undue shock. M is a wrist plate pin by which
the valve rod C can be released from the wrist plate.
The whole purpose of the mechanism is to provide a means for closing the
valves which are at the steam inlet ports, by a sudden action. The
exhaust valves, on the other hand, are not so tripped but are connected
directly with the wrist plate which drives all four of the valves.
The wrist plate or spider has a rocking motion, being driven by an
eccentric rod from the engine-shaft. The mechanism thus described gives
a variable admission as the load varies, but a constant release of the
exhaust and a constant compression to act as a cushion.
[Illustration: _Fig. 77. Angle Valve._]
It gives a high initial pressure in the cylinder, and a sharp cut off,
hence it is found to be very efficient.
Angle Valve.--One of the most useful is the angle valve, which is
designed to take the place of an angle bend or knee in the line of the
piping. The mechanism is the same as in the well known globe valve
construction, the bonnet A being on a line with one of the right-angled
limbs of the body.
The pressure of the fluid should always be on the lower side of the
valve C, coming from the direction of the arrow B, for the reason that
should the steam pressure be constant on the other side, it would be
difficult to repack the gland D without cutting off the steam from the
pipe line.
[Illustration: _Fig. 78. Rotary Valve._]
[Illustration: _Fig. 79. Two-way Rotary._]
Referring back to the illustration of the globe valve, it will be
noticed that the same thing, so far as it pertains to the direction of
the steam, applies in that construction, and a common mistake is to
permit the pressure of the steam to be exerted so that it is constantly
acting against the packing of the spindle.
Rotary Valves.--Two forms of rotary valves are shown, one as illustrated
in Fig. 78, where the rotating part, or plug, A has one straight-way
opening B, which coincides with two oppositely-projecting ports C, D.
The other form, Fig. 79, has an L-shaped opening E through the rotating
plug F, and the casing, in which the plug is mounted has three ports,
one, G, being the inlet, and the other two H, I, at right angles for the
discharge of the fluid.
[Illustration: Fig. 80. Rotary Type.]
[Illustration: _Fig. 81. Two-way Rotary Type._]
Rotable Engine Valves.--So many different forms of the rotable valve
have been made, that it is impossible to give more than a type of each.
For engine purposes the plugs are usually rotated in unison with the
engine shaft, and a single delivery valve of this kind is shown in Fig.
80.
This has three ports in the casing, namely the inlet port A, and two
outlet ports C, D. The plug has a curved cut out channel E, and this
extends around the plug a distance equal to nearly one-half of the
circumference, so that the steam will be diverted into, say, B, for a
period equal to one-quarter turn of the plug, and then into port C, for
the same length of time.
Fig. 81 shows a valve which has a double action. The plug G has two
oppositely-disposed curved channels, H, I, and the casing has a single
inlet port J, and two oppositely-disposed outlet ports K, L.
[Illustration: _Fig. 82. Butterfly Throttle._]
[Illustration: _Fig. 83. Angle Throttle._]
When the plug turns the port L serves to convey the live steam to the
engine, while the other port K at the same time acts as the exhaust, and
this condition is alternately reversed so that L acts as the discharge
port.
Throttle Valves.--The throttle valves here illustrated are those used in
connection with gasoline engines. The best known is the _Butterfly_
valve, shown in Fig. 82, and this is also used as a damper, for
regulating the draft in furnaces and stoves.
This type is made in two forms, one in which the two wings of the valve
are made to swing up or down in unison, and the other, as illustrated,
where the disk A is in one piece, and turns with the spindle B to which
it is fixed.
[Illustration: _Fig. 84. Slide Throttle._]
[Illustration: _Fig. 85. Two-slide Throttle._]
In Fig. 83 the wing C is curved, so that by swinging it around the
circle, the opening of the discharge pipe D is opened or closed.
Another design of throttle is represented in Fig. 84. One side of the
pipe A has a lateral extension B, which is double, so as to receive
therein a sliding plate C, which is easily controllable from the
outside.
Fig. 85 shows a form of double sliding plate, where the double lateral
extensions project out in opposite directions, as at D, D, and within
these extensions are sliding plates which are secured together in such a
way that as one is pushed in the other also moves in, and thus acts in
unison to close or to open the space between them. It is the most
perfect form of throttle valve, as it causes the gases to open directly
into the center of the outgoing pipe.
Blow-off Valves.--The illustration shows a type of valve which is used
on steamboats and very largely on farm boilers throughout the country.
The pipe A from the boiler has cast therewith, or otherwise attached, a
collar B, which has a standard C projecting upwardly at one side, to the
upper end of which is hinged a horizontal lever D, which has a weight at
its other end.
[Illustration: _Fig. 86. Blow-off Valve._]
The upper end of the pipe has a conically-ground seat, to receive a
conical valve E, the stem of which is hinged, as at F, to the level. The
weight may be adjusted to the pressure desired before blowing out and
the only feature in this type of valve is the character of the valve
seat, which is liable, through rust, and other causes, to leak.
Pop, or Safety Valve.--As it has been found more desirable and practical
to use a form of valve which is not liable to deterioration, and also to
so arrange it that it may be manually opened, the _Safety Pop_ valve was
devised.
[Illustration: _Fig. 87. Safety Pop Valve._]
This is shown in Fig. 87, in which the valve seat base A, which is
attached to the top of the boiler, has a cup-shaped outlet B, that is
screwed to it, and this carries a lever C, by means of which the valve
may be manually opened.
A vertical shell D is attached to the cup-shaped portion, and this has a
removable cap E. The valve F is seated within a socket in the base, and
has a disk head, to receive the lower end of a coiled spring G.
The spring is supported in position by a stem H which extends down from
the head, and an adjusting nut I serves to regulate the pressure desired
before the steam in the boiler can act.