An Introduction to Gas Compressors

A compressor is a mechanical device that increases the pressure of a gas/air by reducing its volume. Compressors are similar to pumps.

Both increase the pressure on a fluid and both can transport the fluid through a pipe.

As gases are compressible, the compressor reduces the volume of a gas.

Liquids are relatively incompressible, so the main action of a pump is to pressurize and transport liquids.

Gas compressors are used in various applications where either higher gas pressures or lower volumes of gas are needed:

  • In pipeline transport of purified natural gas to move the gas from the production site to the consumer.
  • In petroleum refineries, natural gas processing plants, petrochemical and chemical plants, and similar large industrial plants for compressing intermediate and end product gases.
  • In refrigeration and air conditioning systems.
  • In gas turbine systems to compress the intake combustion air.
  • In storing purified or manufactured gases in small volume, high pressure cylinders for medical, welding and other uses.
  • In many various industrial, manufacturing and building processes to power all types of pneumatic tools.
  • In pressurized aircraft to provide a breathable atmosphere of higher than ambient pressure.
  • In some types of jet engines (such as turbojets and turbofans) to provide the air required for combustion of the engine fuel. The power to drive the combustion air compressor comes from the jet’s own turbines.
  • In turbochargers and superchargers to increase the performance of internal combustion engines by increasing mass flow.
  • In heavy road transport to provide compressed air for operation of vehicle brakes.


There are many types of equipment, often referred to as prime movers, which can be used to drive a compressor:


  • Steam turbines and gas turbines
  • Natural gas engines, gasoline engines and diesel engines
  • Electric motors
  • Hydraulic power systems


Compressors are classified in to two main categories as show below:

  1. Dynamic (Roto-Dynamic)
  2. Positive Displacement



A typical modern industrial compressed air system is composed of several major subsystems and many sub-components.

Major subsystems include the compressor, prime mover, controls, treatment equipment and accessories, and the distribution system.

The compressor is the mechanical device that takes in ambient air and increases its pressure. The prime mover powers the compressor.

Controls serve to regulate the amount of compressed air being produced.

The treatment equipment removes contaminants from the compressed air and accessories keep the system operating properly.

Distribution systems are analogous to wiring in the electrical world–they transport compressed air to where it is needed.

Compressed air storage can also serve to improve system performance and efficiency.


The prime mover is the main power source providing energy to drive the compressor. The prime mover must provide enough power to start the compressor, accelerate it to full speed, and keep the unit operating under various design conditions.

This power can be provided by any one of the following sources:

  1. Electric motors.
  2. Diesel or natural gas engines
  3. Steam engines or turbines.

Electric motors are the most common type of prime mover.
The are widely available and economical means of providing reliable and efficient power to compressors.

Diesel or natural gas engines are common compressor power source in the oil and gas industries.

Considerations such as convenience, cost, and the availability of liquid fuel and natural gas play a role in selecting an engine to power a compressor.

Although the majority of industrial compressed air systems use electric motors for prime movers, in recent years there has been renewed interest in using non-electric drives such as reciprocating engines powered by natural gas, especially in regions with high electricity rates.

Standby or emergency compressors may also be engine-driven to allow operation in the event of a loss of electrical power.

Maintenance costs for engine-driven systems are significantly higher than those that use electric motors.
The oldest method of driving compressors is through the use of a steam engine or turbine.

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