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.

24.  Q. If, with the automatic brake valve handle in running position, the brake pipe and main reservoir do not stand twenty pounds apart, where would you look for the trouble?

A. Would first learn if the maximum pressure head was properly adjusted, and if it were, would then look for the trouble in the adjustment of the regulating spring in the excess pressure head.

25.  Q. What should be done?

A. The regulating spring should be properly adjusted.

26.  Q. How should the adjustment of the regulating spring in either pressure head be made?

A. By removing the cap nut 25 or 17 and screwing the regulating nut 26 or 18 up or down as may be required.

DEFECTS OF THE GOVERNOR

27.  Q. What would be the effect if one or both of the pin valves leaked?

A. Would cause a delay in opening of the steam valve after the pin valve had seated; and if air leaks by faster than it can escape through the relief port “c”, pressure will accumulate in chamber “b” and force the governor piston downward, so as to partially or wholly close the steam valve 5.

28.  Q. How can you tell if the pin valves leak?

A. Leakage past the pin valve in the maximum pressure head will cause a constant blow at the relief port in all positions of the brake valve; leakage past the pin valve in the excess pressure head will cause a blow in the first three positions of the brake valve only.