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.