Page 35 - Reciprocating Compressors Operation Maintenance
P. 35
22 Reciprocating Compressors: Operation and Maintenance
Isothermal Compression
Adiabatic Compression
Area represents
power saved by
two staging
Combined card on a two
stage reciprocating unit
with perfect interceding
Volume
FIGURE 1-12. Theoretical combined indicator card of a two-stage positive
displacement compressor with perfect interceding.
rocating unit, all cylinders are commonly combined into one unit assem-
bly and driven from a single crankshaft.
For reciprocating compressors, multistaging is used
1. To save power.
2. To limit gas discharge temperature.
3. To limit pressure differential.
Power saving has been demonstrated by the indicator card in Figure 1-8.
Because there is intercooling between stages, there is a reduction in the
maximum gas discharge temperature. Limitation of maximum discharge
temperature is particularly important for safety when holding air in large,
high pressure compressors where distortion of cylinder parts may be a
problem. This is true even though the gas may not become appreciably
more hazardous when heated.
The limitations imposed by high pressure differentials involve avoid-
ance of excess strain in the frame, running gear, and other parts. This is a
