Glossary of Terms
Term | Definition |
---|---|
Aftercooler |
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 desiccant bed. |
Atmospheric Pressure |
The 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. |
Demand |
Flow of air at specific conditions required at a point or by the overall facility. |
Desiccant |
A material having a large proportion of surface pores, capable of attracting and removing water vapour 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%. |
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) vapour mixture is the ratio of the partial pressure of the vapour to the vapour 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. |
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 vapour to the vapour 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. |