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Duplex Operation of Pump Governor
valve 28 seats at almost the instant the brake-valve is lapped.
The benefits obtained from the use of the duplex pump-governor are that a moderate main-reservoir pressure can be regularly carried, reducing the wear of the pump and the rotary valve of the automatic brakevalve, and making the latter easier to operate, etc.; but during an application, the main-reservoir pressure is automatically increased to whatever figure may be considered necessary to effect the prompt release of all brakes in a train of any length, the pump only being required to raise this extra-excess pressure when it is relieved of the duty of brake-pipe supply.
The benefit from the use of brake-pipe pressure as a part of the regulating force in the governor top that normally controls the main-reservoir pressure, is in automatically maintaining a certain excess pressure no matter what the brake-pipe pressure may be; whatever the latter pressure is, the main-reservoir pressure will become just as much higher as the adjustment of the regulating spring in the excess-pressure governor top will permit. An engine with E-T equipment may be regularly carrying 70 pounds pressure in the brake pipe and 90 pounds in the main reservoir; if, then, it becomes necessary to operate the High-Speed Brake, the simple readjustment of the feed valve by turning the wheel handle until the handle-pin strikes the high
pressure stop will raise both pressures to the required amount. Directly, the readjustment of the feed valve raises the brake-pipe pressure to 110 pounds; indirectly, it raises main-reservoir pressure to 130 pounds, because the increase of brake-pipe pressure equally increases the air pressure upon the diaphragm of the excess-pressure governor top: 110 pounds (brake-pipe pressure), plus 20 pounds (spring pressure), equals 130 pounds, the regulating power of excess-pressure governor top, High-Speed Brake.
(Where there is a possibility of having to change from the 70-pound brake to the High-Speed Brake, the high-pressure-right-hand-governor top should not be set at less than 140 pounds, in order that it may operate at a higher figure than the High-Speed pressure adjustment of the excess-pressure top.)
Another important feature is that before commencing, and during, the descent of steep grades, this governor enables the engineer to raise and maintain the brakepipe pressure about 20 pounds above the feed-valve regulation, merely by the use of release position of the automatic brake-valve, the position which should be used during such braking.
While the turning of adjustment nut 18 will increase or decrease the maximum pressure that can be obtained in the main reservoir, remember that turning adjusting nut 26 increases or decreases the amount of
Adjustment of Pump Governor
excess pressure that will be regularly carried; and that in running and holding positions of the automatic brake-valve the location of both hands on the large duplex gauge is governed by the adjustment of the feed valve; but that spring 27 in the excess-pressure governor top keeps the two gauge hands 20 pounds apart.