Motors Part 13
Balanced Slide Valves.--In the chapter pertaining to the steam engine, a simple form of slide valve was shown, and it was stated therein that the pressure of the steam bearing on the valve would quickly grind it down. To prevent this various types of balanced valves have been made, a sample of which is shown in Fig. 64.
The valve chest A has in its bottom two ports C, D, leading to the opposite ends of the cylinder, and within is the sliding valve E, which moves beneath an adjustable plate F connected with the top or cover G of the valve chest.
[Ill.u.s.tration: _Fig. 66. Valve Chest. Double Port Exhaust._]
This is also modified, as shown in Fig. 66, in which case the slide valve H bears against the cover I at two points, so that as there is steam on the upper surface to a slightly greater area than on the lower side, there is sufficient downward pressure to hold it firmly on its seat, and at the same time not cause any undue grinding. This valve also has double exhaust ports J, J.
Balanced Throttle Valve.--Fig. 67 will give a fair idea of the construction of throttle valves, the ill.u.s.tration showing its connection with a simple type of governor.
[Ill.u.s.tration: _Fig. 67. Balanced Throttle-Valve._]
Engine Governors.--Probably the oldest and best known governor for regulating the inlet of steam to an engine, is what is known as the Watt design. This is shown in Fig. 68.
The pedestal A which supports the mechanism, has an upwardly-projecting stem B, to the upper end of which is a collar C, to which the oppositely-projecting pendent arms D are hinged. These arms carry b.a.l.l.s E at their free ends.
[Ill.u.s.tration: Fig. 68. Watt's Governor.]
The lower part of the stem has thereon a sliding collar F, and links G, with their lower ends hinged to the collar, have their upper ends attached to the swinging arms D. The collar has an annular groove at its lower end, to receive therein the forked end of one limb of a bell-crank lever H, the other limb of this lever being connected up with the engine throttle, by means of a link L.
Centrifugal motion serves to throw out the b.a.l.l.s, as indicated by the dotted lines J, and this action raises the bell-crank lever, and opens the throttle valve.
Numerous types of governors have been constructed, some of which operate by gravity, in connection with centrifugal action. Some are made with the b.a.l.l.s adapted to swing downwardly, and thrown back by the action of springs. Others have the b.a.l.l.s sliding on horizontally-disposed arms, and thrown back by the action of springs; and gyroscopic governors are also made which are very effective.
[Ill.u.s.tration: _Fig. 69. The Original Injector._]
Fly wheel governors are not uncommon, which are placed directly on the engine shaft, or placed within the fly wheel itself, the latter being a well known form for engines which move slowly.
Injectors.--The Injector is one of the anomalies in mechanism. It actually forces water into a boiler by the action of the steam itself, against its own pressure. It is through the agency of condensation that it is enabled to do this.
The ill.u.s.tration, Fig. 69, which represents the original type of the device, comprises a sh.e.l.l A, within which is a pair of conically formed tubes, B, C, in line with each other, the small ends of the tubes being pointed towards each other, and slightly separated. The large end of the conical tube C, which points toward the pipe D, which leads to the water s.p.a.ce of the boiler, has therein a check valve E.
The steam inlet pipe F, has a contracted nozzle G, to eject steam into the large end of the conical tube B, and surrounding the nozzle F is a chamber which has a pipe H leading out at one side, through which cold water is drawn into the injector.
Surrounding the conical pipes B, C, is a chamber I, which has a discharge pipe J. The action of the device is very simple. When steam is permitted to flow into the conical tube B, from the nozzle G, it pa.s.ses out through the drain port J, and this produces a partial vacuum to form in the s.p.a.ce surrounding the nozzle G.
As a result water is drawn up through the pipe H, and meeting with the steam condenses the latter, thereby causing a still greater vacuum, and this vacuum finally becomes so great that, with the inrushing steam, and the rapid movement through the conical tubes, past their separated ends, a full discharge through the drain J is prevented.
[Ill.u.s.tration: Fig. 70. Injector with Movable Combining Tube.]
As it now has no other place to go the check valve E is unseated, and the cold water is forced into the boiler through the pipe D, and this action will continue as long as condensation takes place at the nozzle G.
Many improvements have been made on the original form, mostly in the direction of adjusting the steam nozzle, and to provide the proper proportion of flow between the steam and water, as this must be adjusted to a nicety to be most effective.
An example of a movable tube which closes the outlet to the overflow, is shown in Fig. 70. The steam inlet tube A is at one end of the sh.e.l.l, and the outlet tube B to the boiler, at the other end, and intermediate the two is a tube C, with its open flaring end adapted to receive the steam from the tube A. This tube is longitudinally-movable, so that the controlling lever D may move it to and fro.
A chamber E surrounds the nozzle A, and has a water inlet pipe F, while the s.p.a.ce G between the ends of the pipes B, C, has an outlet H, a single check valve I being interposed. In operation the tube C may be adjusted the proper distance from the end of the pipe B, and when the current is once established through the injector, the pipe C may be brought into contact with B, and thus entirely cut out the movement of the water to the overflow.
Feed Water Heater.--An apparatus of this kind is designed to take the exhaust steam from the engine and condense it, and from the condenser it is again returned to the boiler. The water thus used over again goes into the boiler at a temperature of over 180 degrees, and thus utilizes the heat that would otherwise be required to raise the temperature of the water from the natural heat, say 70, up to that point.
In Fig. 71 the ill.u.s.tration shows a typical heater, which comprises an outer sh.e.l.l A, each end having a double head, the inner head B being designed to receive the ends of a plurality of horizontally disposed pipes, and the outer heads C, separated from the inner head so as to provide chambers, one end having one, and the other head being provided with two horizontal part.i.tions D, so the water may be diverted back and forth through the three sets of pipes within the sh.e.l.l.
[Ill.u.s.tration: _Fig. 71. Feed Water Heater._]
The three sets of pipes, E, F, and G, are so arranged that they carry the water back and forth from one head to the other, and for this purpose the water for cooling the steam enters the port H at one end, pa.s.ses through the upper set of pipes E to the other end, then back through the same set of pipes on the other side of a part.i.tion, not shown, and back and forth through the two lower sets of pipes F, G.
The steam enters at the port I at the top of the sh.e.l.l, and pa.s.ses down, as it is condensed, being discharged at the outlet J.
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 ill.u.s.trations and descriptions will give a good idea of the various types in use.
[Ill.u.s.tration: _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 part.i.tion B therein which has a circular aperture.
[Ill.u.s.tration: _Fig. 73. Gate Valve._]
The upper side of the sh.e.l.l 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 part.i.tion. 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 part.i.tion.
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.
[Ill.u.s.tration: _Fig. 74. Globe Valve._]
Gate Valve.--The cylindrical sh.e.l.l A has its ends internally threaded, and is provided, midway between its ends, with a part.i.tion wall B, having a central aperture. The upper side of the sh.e.l.l has an opening to receive the bonnet C, through which the valve stem D pa.s.ses. This stem carries at its lower end a gate E which rests against the part.i.tion 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 pa.s.sage 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 part.i.tion B, the intermediate, horizontally-disposed limb of the part.i.tion 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 part.i.tion.
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 pa.s.sage 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.
[Ill.u.s.tration: _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.