19. Q. How long will the governor remain in this position?
A. Until the main reservoir pressure in chamber "a" under the diaphragm becomes slightly less than the adjustment of the regulating spring 19, when the diaphragm 20 will move down, seating the pin valve, shutting off the flow of air from chamber "a" to chamber "b". The air entrapped above the governor piston will escape to the atmosphere through the relief port "c"; this will allow the governor piston to raise, unseating the steam valve 5, again allowing steam to pass through the governor to the compressor.
20. Q. Is the maximum pressure head cut out in any position of the automatic brake valve?
A. No; as the air that operates this head comes direct from the main reservoir, therefore is not controlled by the brake valve.
21. Q. Is the excess pressure head cut out in any position of the brake valve?
A. Yes; as the air that operates this head comes through the automatic brake valve, and when the handle is moved beyond holding position, the port in the rotary valve seat, through which the air flows to chamber "d" is closed, thereby cutting out this head, leaving the compressor under the control of the maximum pressure head.
22. Q. What is the object of the duplex or double head governor?
A. By use of the duplex governor the main reservoir pressure may be controlled at two different predetermined pressures; as when running along the excess or low pressure head controls the compressor, at the low pressure—usually ninety pounds—this being sufficient to keep the brakes released and fully charged; whereas, in lap position, as following a brake application, the maximum or high pressure head controls the compressor at the maximum pressure used—generally 130 pounds—this for a prompt release and quick recharge of the brakes. From this it will be seen that the compressor has to work against the high pressure only during the time the brake is applied.
23. Q. In what position should the automatic brake valve handle be placed when adjusting the excess pressure head? The maximum pressure head?
A. Running position for the excess pressure head; lap position for the maximum pressure head.