Chapter X: 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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.