The 6 Types of Basic Individual Compressor Controls

Compressor controls are designed to match compressor delivery with compressed air demand, by maintaining the compressor discharge pressure within a highly specified range.  This discharge pressure should be set as low as possible to minimize the energy usage.

Compressor systems are typically composed of multiple compressors delivering air to a common plant air header. The combined capacity of these machines is generally sized to meet the maximum plant air demand. System controls are almost always needed to orchestrate a reduction in the output of the individual compressors during the times of having lower demand. Compressed air systems are usually designed to operate within a fixed pressure range and to deliver a volume of air that varies with system demand. System pressure is monitored and the control system decreases compressor output when the pressure reaches a predetermined level. Compressor output is then increased again when the pressure drops to a lower predetermined level.

There are 6 basic types of individual compressor controls that a person has to take into account when looking into purchasing and using air compression:


  • Turns the motor which drives the compressor on or off in response to a pressure signal (seen on reciprocating and rotary compressors)


  • Allows the motor to run constantly but unloads the compressor when a predetermined pressure is reached. The compressor reloads at a predetermined lower discharge pressure. This is also sometimes referred to as constant speed or constant run control (seen on reciprocating, rotary, and centrifugal compressors).


  • Restricts passage of air to the compressor to progressively reduce compressor output to a specified minimum, when the compressor is then unloaded. This is also referred to as throttling or capacity control (seen on rotary and centrifugal compressors).

Dual/Auto Dual

  • This controller is commonly seen in small reciprocating compressors, allows the selection of either Start/Stop or Load/Unload. When used in a lubricant-injected rotary compressor it provides modulation or load/unload control to a preset reduced capacity. When unloading the addition of an over-run timer will stop the compressor after running unloaded for a preset time.

Variable Displacement

  • This controller allows progressive reduction of the compressor displacement without reducing the channel opening (seen on reciprocating and rotary compressors).

Variable Speed

  • This controller adjusts the compressor capacity by varying the speed of the electric motor driving the compressor in response to system signals.

Learn more about the these six basic compressor controllers and more about other FS Curtis products

Posted on: May 23, 2017, by : Darryl Frierson