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.