glossary of terms
Constant Speed Operation
A compressor that runs continuously between a set load/unload pressure range.
Cycling
The operation of a compressor between its load and unload settings.
Differential (operating range)
The separation between the load and unload pressures of a compressor.
Discharge Line
A tube (copper, Teflon, braided hose, etc.) located between the compressor head and the receiver. The discharge
line itself may be the receiver in some systems.
Idle Speed
Measure of an enginešs RPM while the compressor is unloading. It will only be different from the max speed if the
unit is equipped with a throttle control to slow engine speed.
Intake Unloaders
Valves located in the head of the compressor that unload the compressor when signaled by a pilot device. The
compressor begins to build pressure again once the signal is extinguished.
Load Pressure
Within the operating range, it is the minimum pressure to which the receiver will fall. Also, the minimum pressure
needed to run a tool.
Max Speed
Measure of an enginešs RPM while the compressor is loading.
Pilot Device (auxiliary device)
Used in constant speed applications to actuate other devices.
Pressure Switch
Used in start/stop operation to turn the compressor on at load pressure and off at unload pressure. A pressure
switch can vent discharge line air at the unload pressure if it is an unloading type.
PSI
Pounds per square inch, a measurement of the amount of pressure stored in a receiver.
Receiver
Either a tank, line or other reservoir where compressed air is stored.
SCFM
Standard cubic feet per minute, a flow rating used to describe air delivery at different pressures.
Start/Stop Operation
Operated via a pressure switch, the compressor will stop running at the unload pressure. Once air is used and
pressure drops to the load pressure, the pressure switch turns the compressor back on and begins to build
pressure.
Unloading Device (discharge unloader)
Vents discharge air to atmosphere in constant speed or start/stop operation.
Unload Pressure
Within the operating range, it is the maximum pressure to which the receiver will build.