confined in chamber "b" will escape to the
atmosphere through the vent port "c". The pressure now being removed
from above the governor piston, the spring 9 aided by the steam pressure
under the valve 5, will force the piston upward, unseating the steam
valve 5, allowing steam to pass through the governor to the compressor.

12. Q. When the steam valve is seated, is steam entirely shut off from
the compressor?

A. No; there is a small port drilled through the valve; its purpose is
to maintain a circulation in the steam pipe and keep the compressor
working slowly; thereby preventing condensation when the steam valve is
closed.

13. Q. With the automatic brake valve in release, running, or holding
position, does the maximum pressure head operate?

A. No; as during this time the main reservoir pressure is not
sufficiently high to actuate its diaphragm.

14. Q. Where does the air come from that operates the maximum pressure
head?

A. From the main reservoir direct. (See Fig. 1.)

15. Q. When does the maximum pressure head control the compressor?

A. When the automatic brake valve is in either lap, service or emergency
position, also when the main reservoir cut-out cock is closed.

16. Q. How is the pressure created on top of the diaphragm in the
maximum pressure head?

A. By the regulating spring 19.

17. Q. What is the adjustment of this spring?

A. Spring 19 is adjusted to the maximum pressure desired in the main
reservoir usually 130 pounds.

18. Q. Explain the operation of the governor when the main reservoir
pressure exceeds the tension of the regulating spring 19.

A. When the pressure in chamber "a" exceeds the tension of the
regulating spring 19, the diaphragm 20 is forced upward, unseating the
pin valve, allowing air to flow from chamber "a" to chamber "b" above
the governor piston, forcing it down, shutting off steam and stopping
the compressor.

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