Air Compressor Types
Types of Compressors and Their Use
There are many different types of compressors—rotary screw, reciprocating, centrifugal and more. Reciprocating compressors have pistons and crankshafts typical of an engine; these units are primarily used for special applications or small, inexpensive units for low demand. Rotary screw compressors are used in a variety of applications; these machines typically require less maintenance than reciprocating compressors, especially in constant run situations. Rotary screw compressors and reciprocating compressors are positive displacement pumps, meaning that the pump would theoretically continue to build pressure if the discharge were closed and the unit was supplied with adequate horsepower. Centrifugal compressors will typically cavitate if run past design specifications. They are not positive displacement.
Recriprocating Compressors
Recriprocating units use positive displacement. This means they take in air into a closed space. This intake creates pressure. This air intake is accomplished by use of a piston.
A recriprocating compressor's basic design involves a piston within a cylinder that has one closed end. This cylinder contains one intake valve and one discharge valve. The intake valve takes air into the cylinder and the discharge removes it. The piston's movement draws air in and out of the cylinder.
This type of compressor may be either single or double-acting. This means they either use one side of their piston, or both.
They may also be single or multi-staged. A single-stage compressor completes the entire compression process in a single action--i.e., one piston stroke. A multi-stage compressor pumps a gas from one compressor action to another, such as a series of cylinders to achieve final pressure. A multi-stage compressor is used for various reasons--higher pressures and intercooling being the most common.
Rotary Screw Compressors
Like their cousin the recriprocating compressor, rotary screw compressors employ positive displacement. Their design typically consists of two rotors, also known as screws, that work together to create compression. The rotors spin within a closed space that is usually sealed by injected lubricant. As the rotors move, their grooves trap air and create pressure.
Generally, rotary screw compressors are easy to maintain and operate. They are designed for continuous duty, and cooling of the unit takes place inside the compressor itself.
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