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 device 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 measured 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.