Glossary
- Absolute Pressure
- Total pressure measured from zero (perfect vacuum).
- Actual cubic feet per minute (acfm)
- Flow rate of air at actual operating pressure and temperature.
- Aftercooler
- A heat exchanger used for cooling air discharged from a compressor. Resulting condensate may be removed by a moisture separator following the aftercooler.
- Atmospheric Pressure
- The measured ambient pressure for a specific location and altitude.
- Automatic Sequencer
- A device that operates compressors in sequence according to a programmed schedule.
- Brake Horsepower
- Horsepower delivered to the output shaft of a motor or engine, or the horsepower required at the compressor shaft to perform work.
- 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 absolute discharge pressure to the absolute inlet pressure.
- Cubic Feet per Minute (cfm)
- Volumetric air flow rate per minute converted back to ambient conditions.
- Cycle
- The series of steps that a compressor with unloading performs 1) fully loaded; 2) modulating (for compressors with modulating control); 3) unloaded; and 4) idle.
- Cycle Time
- Amount of time for a compressor to complete one cycle.
- 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 percent.
- Discharge Pressure
- The pressure at the discharge connection of a compressor.
- 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.
- 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.
- Intercooling
- The removal of heat from air or gas between compressor stages.
- Leak
- An unintended loss of compressed air to ambient conditions.
- 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.
- Pneumatic Tools
- Tools that operate by air pressure.
- Positive Displacement Compressors
- Compressors in which successive volumes of air or gas are confined within a closed space and the space mechanically reduced, resulting in compression. These may be reciprocating or rotating.
- Pressure
- Force per unit area, measured in pounds per square inch (psi) or kilo Pascals (kPa).
- Pressure Drop
- Loss of pressure in a compressed air system or component due to friction or restriction.
- 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.
- Sequence
- The order in which compressors are brought online.
- Stages
- A series of steps in the compression of air or a gas. Most plant industrial compressors have 2 stages.
- Standard cfm
- Flow of free air measured and converted to a standard set of reference conditions (14.5 psia, 68°F, and 0 percent relative humidity).
- Start/Stop Control
- A system in which air supply is matched to demand by the starting and stopping of the unit.
- Variable Speed Drive
- An electronic device to vary the speed of a motor enabling it to achieve energy savings at low flows.
- Unload/No load
- Compressor operation in which no air is delivered because the intake is closed or modified not to allow inlet air to be trapped.
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