=Air brake questions=

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?

[Illustration:  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?