How a Reciprocating Compressor Works

A compressor increases the pressure and density of a gas as the volume decreases. Compressors can do this in a number of ways. However, the commonality between all compressors is the fact that they all use some sort of fuel, such as gasoline or electricity, to power whatever compression method they use. Also, because the compressor increases the pressure on the gas, it increases the temperature of the gas. Many other types of compressors are used for various chemicals and fuels that require compression. A reciprocating compressor uses pistons to compress air. The compressor has a similar design to an internal combustion engine; it even looks similar. There is a central crankshaft that drives anywhere from two to six pistons inside cylinders. The crankshaft is generally driven by an external motor. This motor can be electric or internal combustion. However, it determines the total horsepower of the compressor.

Compressing the Gas

As the pistons draw back, gas is injected from an intake valve in the compressor. This gas is injected into the cylinders of the pistons, and is then compressed by the reciprocating action of the pistons. The gas is then discharged either to be used immediately by a pneumatic machine, or stored in compressed air tanks. However, the gas must be stored or used directly from the compressor to prevent it from losing its pressurization.

Components

Frame

The reciprocating air compressor's most obvious component is its frame, also called its crankcase. Usually, this component is shaped like either a square or a rectangle. The main function of the frame is to provide support for the crankshaft.

Piston

The piston is one of the most important components of a reciprocating air compressor. The piston is what actually compresses the air contained within the piston. Most often, a reciprocating compressor will have pistons made out of aluminum alloy. However, if the model of reciprocating compressor uses non-lubricated pistons, they will most commonly be made out of cast iron.

Compression Rings

The compression rings help the pistons to do their work. They function as seals against the pressure of the air as the piston compresses it. The compression rings fit onto several grooves cut into the piston. The number of compression rings will depend upon the diameter of the piston as well as the pressure present in the compressor.

Oil Scrapper Rings

Oil scrapper rings are only present in certain types of air compressors. Splash-lubricated oil compressors usually have scrapper rings. These rings are used to direct the oil caught by the compression rings toward the crankcase.

Crank Shaft

The crank shaft is the component that actually motivates the reciprocating compressor. The crank shaft is usually made from iron with several other sub-components such as crank pins holding the pieces of the shaft together, and a flywheel on the end of the shaft closest to the crank.

Cylinder Head

Every reciprocating compressor has a cylinder head, which is usually made from cast iron. Sometimes cylinder heads are referred to as simply cylinders. The cylinders are what the air flows through. They are designed to allow as streamlined a passage of air as possible, so that as little of the pressure generated from its pistons is exhausted. Cylinders fasten to the body of the compressor as tightly as possible, which also helps minimize pressure loss.