Page 148 - Reciprocating Compressors Operation Maintenance

I 34 Reciprocating Compressors: Operation and Maintenance

(from)
Suction tine

1
Discharge HneaE """"" H^v^

mean piston speed

FIGURE 3-8. Piston stroke position superimposed on pV-diagram (Source:
Hoerbiger Corporation of America, Ft. Lauderdale, Florida).

Compression

With both suction and discharge valve closed, the piston's return
stroke to the left compresses the gas in the cylinder and reduces its vol-
ume while it increases its temperature and pressure, until the pressure
exceeds the desired delivery pressure, P, by the amount sufficient to open
the discharge valve (point B in the PV-diagram).
This excess pressure is necessary to overcome the equalization static
pressure on the valve plate and to lift the valve plate against the spring load.

Gas Discharge

When the discharge valve opens, the excess pressure decreases in
diminishing waves to P 2. Just before the piston reaches the end of its left-