COMPRESSED AIR SYSTEM GLOSSARY "A through C"
Absolute Temperature - See Temperature, Absolute.
Absorption - The chemical process by which a hygroscopic desiccant, having a high affinity with water, melts and becomes a liquid by absorbing the condensed moisture.
Actual Capacity - Quantity of gas actually compressed and delivered to the discharge system at rated speed and under rated conditions. Also called Free Air Delivered (FAD).
Adiabatic Compression - See Compression, Adiabatic.
Adsorption - The process by which a desiccant with a highly porous surface attracts and removes the moisture from compressed air. The desiccant is capable of being regenerated.
Air Receiver - See Receiver.
Air Bearings - See Gas Bearings.
Aftercooler - A heat exchanger used for cooling air discharged from a compressor. Resulting condensate may be removed by a moisture separator following the aftercooler.
Ambient Temperature - the temperature of the surrounding environment; technically, the temperature of the air surrounding a power supply or cooling medium; abbreviated [ABM]
Atmospheric Pressure - The measured ambient pressure for a specific location and altitude.
Automatic Sequencer - A device which operates compressors in sequence according to a programmed schedule.
Brake Horsepower (bhp) - See Horsepower, Brake.
Capacity - The amount of air flow delivered under specific conditions, usually expressed in cubic feet per minute (cfm).
Capacity, Actual - The actual volume flow rate of air or gas compressed and delivered from a compressor running at its rated operating conditions of speed, pressures, and temperatures.
Actual capacity is generally expressed in actual cubic feet per minute (acfm) at conditions prevailing at the compressor inlet.
Capacity Gauge - A gauge that measures air flow as a percentage of capacity, used in rotary screw compressors
Check Valve - A valve which permits flow in only one direction.
Clearance - The maximum cylinder volume on the working side of the piston minus the displacement volume per stroke. Normally it is expressed as a percentage of the displacement volume.
Clearance Pocket - An auxiliary volume that may be opened to the clearance space, to increase the clearance, usually temporarily, to reduce the volumetric efficiency ofa reciprocating compressor.
Compressibility - A factor expressing the deviation of a gas from the laws of thermodynamics. (See also Supercompressibility)
Compression, Adiabatic - Compression in which no heat is transferred to or from the gas during the compression process.
Compression, Isothermal - Compression is which the temperature of the gas remains constant.
Compression, Polytropic - Compression in which the relationship between the pressure and the volume is expressed by the equation PVn is a constant.
Compression Ratio - The ratio of the absolute discharge pressure to the absolute 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.
Critical Pressure - The limiting value of saturation pressure as the saturation temperature approaches the critical temperature.
Critical Temperature - The highest temperature at which well-defined liquid and vapor states exist. Sometimes it is defined as the highest temperature at which it is possible to liquify a gas by pressure alone.
Cubic Feet Per Minute (cfm) - Volumetric air flow rate.
cfm, free Air - cfm of air delivered to a certain point at a certain condition, converted back to ambient conditions.
Actual cfm (acfm) - Flow rate of air at a certain point at a certain condition at that point.
Inlet cfm (icfm) - Cfm flowing through the compressor inlet filter or inlet valve under rated conditions.
Standard cfm - 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.
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