Page 153 - Root Cause Failure Analysis

Compressors 141

- DISCHARGE
IN LET

Figure 10-12 Annular-ring valves (Gibbs 1971).

Cylinder Orientation Orientation of the cylinders in a multistage or multicylinder
compressor directly affects the operating dynamics and vibration level. Figure 10-13
illustrates a typical three-piston, air-cooled compressor. Since three pistons are ori-
ented within a 120" arc, this type of compressor generates higher vibration levels than
the opposed piston compressor illustrated in Figure 10-14.

Pe~ormance
Refer back to the previous discussion of the laws of thermodynamics governing all
compressors. Reciprocating-compressor performance is governed almost exclusively
by operating speed. Each cylinder of the compressor will discharge the same volume,
excluding slight variations caused by atmospheric changes, at the same discharge
pressure each time it completes the discharge stroke. As the rotation speed of the com-
pressor changes, so does the discharge volume.

The only other variables that affect performance are the inlet-discharge valves, which
control flow into and out of each cylinder. Although reciprocating compressors can
use a variety of valve designs, it is crucial that the valves perform reliably. If they are
damaged and fail to operate at the proper time or do not seal properly, overall com-
pressor performance will be reduced substantially.