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Compressed Air System Glossary


Air Compressor Definition: An Air Compressor is a device that converts power into potential energy . The energy is stored in pressurised air (compressed air) there are a few different types of air compressors

Absolute pressure: Total pressure measured from absolute zero.

Aftercooler: Heat exchanger for cooling air discharged from air compressor.

Atmospheric pressure: Pressure above absolute zero at a specific location and altitude.

Capacity: The amount of air flow delivered or required under some specific conditions. May be stated as acfm, scfm, or cfm FAD.

Cubic feet of air per minute (cfm): Volume delivery rate of air flow.

Cubic feet of air per minute, free air (cfm FAD): cfm of air delivered to some specific point and converted back to ambient air (free air) conditions.

Actual cubic feet per minute (acfm): Flow rate of air measured at some reference point and based on actual conditions at that reference point.

Inlet cubic feet per minute (icfm): cfm flowing through the compressor inlet filter or inlet valve under rated conditions.

Standard cubic feet per minute (scfm): Flow of free air measured at a reference point and converted to a standard set of reference conditions (e.g., 14.5 psia, 68┬░F, and 0% relative humidity).

Demand: Flow of air under specific conditions required at a particular point.

Discharge pressure, rated: Air pressure produced at a reference point.

Discharge pressure, required: Air pressure required at the system inlet.

 Displacement: Amount of air (in cfm) displaced by the compressor piston under no load, discharging directly to the atmosphere.

Dual control: Load/unload control system that maximizes compressor efficiency. Compressor is normally operated at full load or idle, and is stopped and restarted automatically depending on demand.

Free air: Air at ambient conditions of temperature, humidity, and atmospheric pressure at any specific location.

Inlet pressure: The total pressure at the inlet flange of the compressor.

Load factor: Ratio of the average compressor load to the maximum rated compressor load during a given period of time.

Modulating control: Control system which will run the compressor at reduced output to accommodate demand variations. Running a compressor at less than full load results in a drop in compressor efficiency and thus an increase in operating costs.

Pressure: Force per unit area.

Pounds per square inch (psi): Force per unit area exerted by compressed air.

Pounds per square inch absolute (psia): Absolute pressure above zero pressure.

Pounds per square inch gauge (psig): Pressure difference between absolute pressure (psia) and ambient pressure.

Pounds per square inch differential (psid): Pressure difference between two defined points in the system.

Pressure dew point: Temperature at which water will begin to condense out of air at a given pressure.

Pressure drop: Loss of pressure in a compressed air system due to friction or flow restriction.