Page 57 - Reciprocating Compressors Operation Maintenance

C H A F T E R 2

Design and Materials for

Reciprocating Compressor

Components

Today's modern, heavy-duty, continuous-service reciprocating com-
pressor cylinders can be attached to a single horizontal or vertical frame.
When more than one cylinder is used, the various configurations are
almost endless. As previously seen, these machines range from simple
one-cylinder, single-stage compressors for air service to multi-stage,
multi-service process gas compressors.
Regardless of the service, from the smallest to the largest, reciprocat-
ing compressors share both the same principles of operation and the
same basic design features. Figure 2-1 illustrates a modern two-cylinder,
two-stage compressor with intercooling between stages.
Some type of driver rotates a crankshaft, which converts rotary motion
into reciprocating motion. The crankshaft is usually made from a steel
forging and is supported by at least two main bearings.
The number of main bearings increases with the number of throws on
the crankshaft that are required for the number of cylinders used. A typi-
cal crankshaft is counter-weighted, either integral with the shaft or sepa-
rate from and bolted to it, in order to offset the effect of the unbalanced
forces associated with a reciprocating compressor.
Most modern compressors use anti-friction or sleeve main bearings,
although there are many older design compressors still in service that use
two- or three-piece, adjustable babbitted bearings. This practice was

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