Fig. 3: Diagrammatic View, Down Stroke.
In the meantime the air above the piston, being compressed, will hold the upper receiving valve 86a to its seat, and when the pressure is slightly greater than that in the main reservoir, this pressure acting under the upper discharge valve 86c, will lift this valve from its seat and now the air will be free to flow through passage "G" to the main reservoir connection. On the down stroke the action is similar, air is taken in through the upper receiving valve 86a, while the air below the piston is being compressed and forced past the lower discharge valve 86d, to the main reservoir. (See Fig. 3.)
46. Q. What lift should the air valves have?
A. All valves should have a lift of three thirty-second of an inch.
47. Q. At what speed should the compressor be run to obtain the best results?
A. At 100 to 120 single strokes per minute.
48. Q. What kind of oil should be used in the air end of the compressor and on the swab?
A. Valve oil.