The operation of this governor is as follows: the wheel 8 is screwed down so as to permit the valve 10 to be unseated by the excess of pressure on the upper side of the valve, permitting steam to pass through the openings A and B to the pump. A connection is made from the train-pipe to the upper end of the governor, and the compressed air passes around the stem 14 to the upper side of the diaphragm plate 18, which is held to its position by the spring 16, which latter is of sufficient strength to resist a pressure of, say, seventy pounds per square inch on diaphragm. As soon as the air-pressure on the diaphragm 18 exceeds this amount, it forces the diaphragm down, unseating the valve 13, and allowing the steam on the upper side of the valve 10 to escape through the exhaust 6, which causes an excess of steam-pressure on the lower side of the valve 10, forcing the valve against its seat, and cutting off the supply of steam to the pump.
When the pressure in the train-pipe is diminished by applying the brakes, the diaphragm is restored to the position shown by the action of the spring 16. The valve 13 is seated by the spring 12; and the steam-pressure, passing through the port C, accumulates on the upper side of the valve 10, forcing it down, and opening the passage for steam to the pump until the air-pressure is again restored to the required limit of seventy pounds.
CHAPTER XXV.
THE EAMES VACUUM BRAKE.
OPERATION OF THE BRAKE.
The Vacuum Brake, as the name implies, is operated by means of a vacuum which is formed in the connections that act the part of the cylinder in the air-brake. With an air-brake, compressed air is made to do the work of applying the brakes by moving a piston to which the brake-lever is attached, the air being carried throughout the train by means of iron pipes and rubber hose: with the vacuum brake the work is done in a similar way with similar connections; but, instead of compressed air being forced inside the pipes and apparatus, all the air is exhausted out, and the natural pressure of the atmosphere is made to do the work.
THE DIAPHRAGM.
Fig. 35.