Air Compressor Glossary

Alphabetical Definitions of Common Air Compressor Terms

• After Cooler

  • A heat exchanger used for cooling air discharged from a compressor. Resulting condensate may be removed by a moisture separator following the aftercooler.

• Air Dryer

  • A devise that removes moisture from compressed air. Typically accomplished by cooling the air through a refrigerator or dessicant bed.

• Atmospheric Pressure

  • he measured ambient pressure for a specific location and altitude in PSI (pounds per square inch).

• Automatic Sequencer

  • A device which operates compressors in sequence according to a programmed schedule.

• Capacity

  • The amount of air flow delivered under specific conditions, usually expressed in cubic feet per minute (CFM).

• Check Valve

  • A valve which permits flow in only one direction.

• Compression Ratio

  • The ratio of the discharge pressure to the inlet pressure.

• Constant Speed Control

  • A system in which the compressor is run continuously and matches air supply to air demand by varying compressor load.

• Cubic Feet Per Minute (CFM)

  • Volumetric air flow rate.

• Cut-In/Cut-Out Pressure

  • Respectively, the minimum and maximum discharge pressures at which the compressor will switch from unload to load operation (cut in) or from load to unload (cut out).

• Cycle

  • The series of steps that a compressor with unloading performs; 1) fully loaded, 2) modulating (for compressors with modulating control), 3) unloaded, 4) idle.

• Cycle Time

  • Amount of time for a compressor to complete one cycle.

• Desiccant

  • A material having a large proportion of surface pores, capable of attracting and removing water vapor from the air.

• Dew Point

  • The temperature at which moisture in the air will begin to condense if the air is cooled at constant pressure. At this point the relative humidity is 100%.

• Demand

  • Flow of air at specific conditions required at a point or by the overall facility.

• Discharge Pressure

  • Air pressure produced at a particular point in the system under specific conditions measured in PSI (pounds per square inch).

• Discharge Temperature

  • The temperature at the discharge flange of the compressor.

• Filters

  • Devices for separating and removing particulate matter, moisture or entrained lubricant from air.

• Full-Load

  • Air compressor operation at full speed with a fully open inlet and discharge delivering maximum air flow.

• Gas

  • One of the three basic phases of matter. While air is a gas, in pneumatics the term gas normally is applied to gases other than air.

• Gauge Pressure

  • The pressure determined by most instruments and gauges, usually expressed in psig. Barometric pressure must be considered to obtain true or absolute pressure (PSIG).

• Horsepower, Brake

  • Horsepower delivered to the output shaft of a motor or engine, or the horsepower required at the compressor shaft to perform work.

• Humidity, Relative

  • The relative humidity of a gas (or air) vapor mixture is the ratio of the partial pressure of the vapor to the vapor saturation pressure at the dry bulb temperature of the mixture.

• Inlet Pressure

  • The actual pressure at the inlet flange of the compressor typically measure in PSIG.

• Intercooling

  • The removal of heat from air or gas between compressor stages.

• Leak

  • An unintended loss of compressed air to ambient conditions.

• Load Time

  • Time period from when a compressor loads until it unloads.

• Load/Unload Control

  • Control method that allows the compressor to run at full-load or at no load while the driver remains at a constant speed.

• Modulating Control

  • System which adapts to varying demand by throttling the compressor inlet proportionally to the demand.

• Multi-Stage Compressors

  • Compressors having two or more stages operating in series.

• Piston Displacement

  • The volume swept by the piston; for multistage compressors, the piston displacement of the first stage is the overall piston displacement of the entire unit.

• Pressure

  • Force per unit area, measured in pounds per square inch (PSI).

• Pressure Dew Point

  • For a given pressure, the temperature at which water will begin to condense out of air.

• Pressure Drop

  • Loss of pressure in a compressed air system or component due to friction or restriction.

• Pressure Range

  • Difference between minimum and maximum pressures for an air compressor. Also called cut in-cut out or load-no load pressure range.

• Receiver

  • A vessel or tank used for storage of gas under pressure. In a large compressed air system there may be primary and secondary receivers.

• Reciprocating Compressor

  • Compressor in which the compressing element is a piston having a reciprocating motion in a cylinder.

• Relative Humidity

  • The ratio of the partial pressure of a vapor to the vapor saturation pressure at the dry bulb temperature of a mixture.

• Specific Gravity

  • The ratio of the specific weight of air or gas to that of dry air at the same pressure and temperature.

• Speed

  • The speed of a compressor refers to the number of revolutions per minute (rpm) of the compressor drive shaft or rotor shaft.

• Unload

  • (No load) Compressor operation in which no air is delivered due to the intake being closed or modified not to allow inlet air to be trapped.

• Valves

  • Devices with passages for directing flow into alternate paths or to prevent flow.