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Understanding the
Air Compressor Language
Absolute Pressure is the entire pressure
measured from zero.
After-cooler is a heat exchanger which is utilized for cooling air which
has been discharged from a compressor. The condensation that results may
be removed by a moisture separator following the after-cooler.
Brake Horsepower (bhp) is needed at the compressor shaft to operate. It
is also horsepower that is transported to the output shaft of a motor or
engine.
Capacity is often conveyed in cubic feet per minute (cfm). It is the
quantity of the flow of air which is transported under explicit
circumstances.
Actual capacity is the precise volume rate of flow of air or gas
compressed and transported from a compressor which is operating at its
precise degree of speed, pressures and temperatures. Actual capacity is
most often stated in actual cubic feet per minute (acfm) with conditions
that exist at the compressor inlet.
Adiabatic compression occurs without the transference of heat or gas
during the compression process.
Isothermal compression occurs when the temperature of the gas remains
stable.
Compression Ratio is the ratio of the absolute discharge pressure to the
ratio of the absolute inlet pressure.
Actual Cfm (acfm) represents the flow rate of air at a certain point at
a particular condition at that point.
Inlet Cfm occurs under rated conditions in which the inlet Cfm flows
through the compressor inlet filter or inlet valve.
Standard Cfm represents the flow of free air which is measured, then
changed to a typical set of reference conditions, such as 14.5 psia, 68°
F, and 0% relative humidity.
Cycle is the sequence of steps performed by a compressor which is
unloading. These steps are as follows: fully loaded; adjusted (used for
compressors with adjusted controls); unloaded; and idle.
Cycle time is the period of time that it
take a compressor to complete one cycle.
Degree of Inter-cooling is the difference in air or gas temperature
between the inlet of the compressor and the outlet of the intercooler.
Discharge Pressure is the air pressure that is generated at a certain
point in the system under certain conditions.
Discharge Temperature is the temperature at the discharge projection
(flange) of the compressor.
Compression Efficiency is the ratio of hypothetical power to actual
power passed on to the air or gas transported by the compressor.
Full-Load is an air compressor operating at the full rate of speed with
an inlet fully open and discharged delivering a maximum flow of air.
Gauge Pressure is the pressure which is established by the majority of
the instruments and gauges. It is most often stated in psig. In order to
obtain accurate or absolute pressure, barometric pressure must be
considered.
Theoretical or Ideal Horsepower is the horsepower that is required to
isothermally compress the air or gas transmitted by the compressor at
certain conditions.
Inlet Pressure is the real pressure at the inlet projection (flange) of
the compressor.
Intercooling involves removing heat from air or gas between compressor
stages.
Leak is the unintentional loss of compressed air to conditions on all
sides.
Load Factor involves the compressor load average ratio to the maximum
rated compressor load over a certain period of time.
Load Time is the period of time from compressor loading until unloading.
Load-Unload Control involves a method of control that permits the
compressor to operate at full load or at no load when the driver
maintains a constant speed.
Modulating Control is a system which adjusts to differing demands by
which the compressor inlet is throttled in proportion to the demand.
Perfect Intercooling is the condition whereby the temperature of the air
exiting the intercooler is equal to the air temperature at the intake of
the compressor.
Pressure Drop is when friction or restriction causes a loss of pressure
in a compressed air system.
Rated Capacity is the volume rate of the air flow of rated pressure at a
particular point.
Rated Pressure is the operating pressure by which performance of the
compressor is calculated.
Specific Power is a measure of the efficiency of air compressor, most
often in the form of bhp/100 acfm or acfm/bhp.
Standard Air is the definition used in ISO standards which has been
established by The Compressed Air & Gas Institute and also PNEUROP
(European Committee of Manufactures of Compressors, Vacuum Pumps and
Pneumatic Tools). It is air at 14.5 psia (1 bar); 68F (20C) and dry (0%
relative humidity).
Surge is a phenomenon in centrifugal compressors wherein a flow reversal
and an unstable operation are the results of a reduced flow rate.
Theoretical Power is the power that is needed to compress a gas
isothermally through a certain range of pressures.
Torque refers to the driving couple of a motor or a machine.
Total Package Input Power refers to the entire electrical power
contribution to a compressor. This would include the drive motor,
cooling fan, motors, controls, etc.
Unload (or No Load) is the operation of the compressor whereby no air is
delivered because the intake has been closed or modified so that it will
not allow inlet air to be trapped.
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Understanding the
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