Reciprocating compressor

A reciprocating compressor compresses gas the way a piston engine burns fuel, just run for a different purpose: a piston moves down a cylinder on the suction stroke to pull gas in through a valve, then moves back up on the compression stroke, closing that valve and forcing the gas out through a discharge valve at higher pressure. Most field packages use multiple cylinders and stages to reach the pressure ratio needed, and the whole unit is driven by a natural gas engine or electric motor sized to the horsepower required.

Reciprocating units dominate wellhead, gathering, and vapor recovery service because they handle a wide range of pressures and volumes efficiently and can be packaged small enough to sit on a single wellsite. They need more routine maintenance than a screw or centrifugal unit — valves, packing, and rings all wear with use — which is exactly why service and maintenance is such a large part of a compression company's business. On the show, guests describe building small electric reciprocating units specifically for vapor recovery and wellhead duty, and separately describe reciprocating engines as the standard choice for smaller-scale power generation before a project is big enough to justify a combined-cycle plant.

The tradeoff with reciprocating equipment is maintenance frequency versus flexibility: because it compresses gas in discrete strokes rather than continuously, it tolerates a wider range of gas compositions and pressure swings than a screw or centrifugal unit, which is exactly what a small, changeable wellsite throws at it. That flexibility is why reciprocating compressors remain the default choice for wellhead, gathering, and vapor recovery duty even though they demand more frequent valve, packing, and ring service than the simpler continuous-compression alternatives.