A. Oil should be used sparingly in the low pressure cylinder, but more is required in the high pressure cylinder, owing to higher temperature. A good quality of valve oil should be used.
172. Q. How is the steam end of the compressor affected by the use of too much oil?
A. This may cause the compressor to short stroke, and where the piston type of valve is used, may cause the compressor to stop.
L-T EQUIPMENT
AUTOMATIC CONTROL VALVE
173. Q. What is the duty of the control valve?
A. To admit air from the main reservoir to the locomotive brake cylinders when applying the brakes; to automatically maintain the brake cylinder pressure against leakage; to develop the proper brake cylinder pressure regardless of piston travel; and to exhaust the air from the brake cylinders when releasing the brake, in all automatic applications of the brake.
174. Q. Explain the operation of the control valve when making an automatic service application of the brake.
A. Air enters the control valve at the connection marked "BP" (Fig. 21), which leads to chamber "F" above the piston 3, forcing it down, uncovering the feed groove "G" in the bushing, allowing air to feed past the piston into the slide valve chamber, and then through port "H" to the auxiliary reservoir. The air will feed through in this manner until the auxiliary reservoir and brake pipe pressure equalize. When a gradual reduction of brake pipe pressure is made, it will be felt in chamber "F", above piston 3, creating a difference in pressure on the two sides of the piston, which will cause it to move upward.
