Condition Monitoring, Troubleshooting and Reliability in Rotating Machinery

18Estimating Reciprocating Compressor Gas Flows

Simple hand calculations can be used to evaluate reciprocating compressors in the field.

By Robert X. Perez

Reciprocating compressors, like the one depicted in Figure 18.1, are commonly used to move gases throughout the petrochemical industry. These types of compressors commonly employ one or more reciprocating pistons, which are driven off a common crankshaft, to compress gas and move it from a lower to higher pressure. There are multiple design and operating factors, such as piston and rod geometry, speed, and operating pressures, that affect the actual flow realized under operating conditions.

The purpose of this brief discussion is to explain to readers how they can estimate the flow capabilities based on readily available information. To calculate compressor flows, the users must understand a cylinder’s swept volume, clearance volume, volumetric efficiency, and compression ratio. Once these basic factors that affect flow are understood, then field troubleshooting and assessments are possible.

Figure 18.1 Single stage reciprocating compressor.

Swept Volume

The swept volume of a compressor cylinder is equal to the area of the compressor piston times the piston’s stroke length, i.e., Swept volume = piston area x stroke length (see Figure 18.2). If a cylinder had a 100% volumetric efficiency, then the flow created by a cylinder ...