Compressor Governor

1. Q. When steam is first turned on, what must it pass through before entering the compressor?

A. The compressor governor.

2. Q. What does Fig. 1 represent?

A. This shows a sectional view of the SF compressor governor in open position.

3. Q. What is the duty of the compressor governor?

A. To automatically regulate the main reservoir pressure by controlling the steam to the compressor.

4. Q. How are the regulating portions of the governor designated?

A. The one having two pipe connections and a light regulating spring is known as the excess pressure head; the other, with a single pipe connection and heavy regulating spring, as the maximum pressure head.

5. Q. When does the excess pressure head control the flow of steam to the compressor?

A. When the automatic brake valve is in any one of its first three positions; namely, release, running and holding positions.

6. Q. With the automatic brake valve in release, running or holding position, what pressure is in chamber "f" above the diaphragm? In chamber "d" below the diaphragm?

Fig. 1: The SF-4 Compressor Governor. Connections: FVP, Feed Valve Pipe. ABV, Automatic Brake Valve. MR, Main Reservoir. B, From Boiler. P, To Air Pump.

A. Air, at feed valve pipe pressure, enters at the connection marked "FVP" and flows to chamber "f" above the diaphragm; this pressure acts in conjunction with the regulating spring 27 in creating the total pressure on the diaphragm. Air at main reservoir pressure flows through the automatic brake valve to the connection marked "ABV" to chamber "d" under the diaphragm.

7. Q. At what pressure is the regulating spring in the excess pressure head adjusted?

A. Usually twenty pounds.

8. Q. With the spring adjusted at twenty pounds, what will be the total pressure on the upper side of the diaphragm?

A. Twenty pounds, plus the pressure in the feed valve pipe.

9. Q. With the feed valve adjusted at seventy pounds, and the regulating spring at twenty pounds, what pressure will be had in the main reservoir when the governor stops the compressor?

A. Ninety pounds.

10. Q. Explain the operation of the governor in controlling the compressor when a main reservoir pressure of ninety pounds is reached.

A. When the main reservoir pressure in chamber "d" slightly exceeds the pressure on top of the diaphragm it will move upward, carrying the pin valve with it. The air in chamber "d" passes by the unseated pin valve through port "b" into chamber "b" above the governor piston, forcing it downward, seating the steam valve 5, thus shutting off the steam to the compressor.

11. Q. How long will the governor remain in this position?

A. Until the main reservoir pressure falls below ninety pounds, when the combined spring and air pressure in chamber "f" will force the diaphragm 28 down, seating the pin valve. This shuts off the supply of air from chamber "d", and the air 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 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.

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.

29. Q. What would be the effect if the relief port "c" stopped up?

A. The compressor will not start promptly after the pin valve seats.

30. Q. What would be the effect if the drain port "W" were stopped up?

A. Steam leaking into the chamber under the governor piston will form a pressure and prevent the piston being forced downward to close the steam valve; the compressor will therefore continue to work until the main reservoir pressure is about equal to boiler pressure.

31. Q. If the pipe leading from the feed valve pipe to the excess pressure head of the governor breaks, what effect will it have on the compressor?

A. The compressor will stop when the main reservoir pressure reaches about forty-five pounds.

32. Q. If the pipe breaks, what should be done?

A. Plug the end toward the feed valve and put a blind gasket in the pipe leading from the automatic brake valve to the governor, at the connection marked ABV.

33. Q. If the pipe leading from the automatic brake valve to the governor breaks, what should be done?

A. Plug the pipe toward the brake valve; the compressor will now be controlled by the maximum pressure head.

34. Q. If the pipe leading from the main reservoir to the maximum head of the governor breaks, what should be done?

A. Plug the main reservoir end of the pipe. The excess pressure head will now control the compressor in the first three positions of the automatic brake valve handle, but will have no control after the handle is moved as far as lap position.

Parasite Governor

35. Q. What is the purpose of the parasite governor, and where is this governor located?

A. This governor is located in the pipe connection between the main reservoir and parasite reservoir, and its purpose is to control the flow of air from the main to the parasite reservoir.

36. Q. What is the purpose of the parasite reservoir?

A. It is here that air is stored for use in all air operated devices on the locomotive, except the brake.

37. Q. Explain the operation of the parasite governor.

A. The operation of this governor is much the same as the compressor governor, and differs only in that the supply valve is open when it is in its lower position.

38. Q. At what pressure is the regulating spring adjusted?

A. About fifteen pounds.

39. Q. What pressure is required in the main reservoir before air is admitted to the parasite reservoir?

A. At least fifteen pounds above that in the brake pipe.

40. Q. What pressure is obtained in the parasite reservoir?

A. The same as that in the main reservoir, when the main reservoir pressure is fifteen pounds greater than that in the brake pipe.

41. Q. What will prevent the charging of the parasite reservoir, and what should be done?

A. This may be caused by the feed valve being improperly adjusted, sticking in open position or leakage of main reservoir air past the valve to the feed valve pipe and governor top.