Air Dryer – A devise that removes moisture from compressed air. Typically accomplished by cooling the air through a refrigerator or dessicant bed.
Atmospheric Pressure – The measured ambient pressure for a specific location and altitude in PSI.
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.