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valve releases air pressure trapped in the discharge line between the compressor pump and the non-
return valve. This allows the compressor to re-start more easily without being under load at the
outset.
The pressure switch on electric-powered, oil lubricated, single-stage compressors is factory pre-set
with cut-in and cut-out pressures of approximately 650 kPa (94 psi) and 870 kPa (126 psi),
respectively. This range is ideal for the vast majority of compressed air applications supplied by an
electric air compressor. Most pneumatic tools are designed for a supply pressure of only 620 kPa
(90 psi). Unless absolutely necessary for a special application, compressor operation at higher
pressures is not recommended because it increases electricity consumption and compressor pump
wear and tear. For reference, these compressors can be adjusted up to a cut-out pressure not
exceeding 1,000 kPa (145 psi).
For electric-powered, oil lubricated, two-stage compressors the pressure switch is factory pre-set
with cut-in and cut-out pressures of approximately 950 kPa (138 psi) and 1,200 kPa (174 psi),
respectively. These compressors should not be adjusted to a higher cut-out pressure.
The pressure switch on electric-powered, oil free compressors – both single-stage and two-stage – is
factory pre-set with cut-in and cut-out pressures of approximately 650 kPa (94 psi) and 870 kPa (126
psi), respectively. These compressors should not be adjusted to a higher cut-out pressure.
On engine-driven models the pilot valve regulates the operation of the compressor pump to maintain
the air receiver tank pressure between the pre-set cut-in and cut-out levels. Rather than turn off the
engine when the cut-out pressure is reached, which would necessitate physically re-starting the
engine if more compressed air is required, the pilot valve actuates the head unloader in each cylinder
head to keep the inlet valve open. Air can be felt pulsing in and out of the inlet air filter whenever the
compressor pump is in this “unloading” mode. When the pressure drops to the cut-in value, the pilot
valve deactivates the head unloader in each cylinder whereupon the compressor enters into
“pumping” mode.
An added feature to reduce fuel consumption, noise emission and wear and tear is the automatic
throttle control system whereby engine speed is reduced to idle whenever the compressor is in
unloading mode and subsequently increased to maximum revolutions when the compressor switches
to pumping mode.
On engine-driven, single-stage compressors the pilot valve is factory pre-set with cut-in and cut-out
pressures of approximately 800 kPa (116 psi) and 1,000 kPa (145 psi), respectively. This is the
optimum range for most applications using an engine-driven air compressor and it should not be
adjusted higher.
For engine-driven, two-stage compressors the pilot valve is factory pre-set with cut-in and cut-out
pressures of approximately 1,000 kPa (145 psi) and 1,200 kPa (174 psi), respectively. It should not be
adjusted higher.
If the pressure switch or pilot valve does not shut off the compressor pump discharge into the air
receiver tank at the cut-off pressure setting, the safety valve will protect the air tank against over
pressurising by automatically releasing air when the pressure exceeds a pre-set value.
Airmac air receiver tanks are designed and manufactured to comply with the requirements of
Australian Standard AS 1210 and all Australian Workplace Health and Safety Regulations. A copy of
the Manufacturer’s Data Report (as per AS 4458) is available from your Airmac dealer or Glenco Air &
Power Pty Ltd upon request.
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