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V100-VL400 User Manual – General Description
5. REGULATION SYSTEM
Each suction valve is fitted with an unloader which
incorporates an air operated diaphragm and spring-
loaded fork to hold the suction valves off their seats
and cause the compressor to run unloaded. The
unloader forks are actuated by the regulation
system to provide the required control of the
compressor.
The unloaders may also be operated manually to
enable the compressor to be started up initially in
an off-load condition.
The normal method of regulation is by Air Governor
Control. An alternative method using an additional
control panel is available which allows the
compressor to be operated in either the Continuous
mode or the Automatic Start/Stop mode. The panel
can also control a stand-by compressor or a
multiple installation.
5.1 Air Governor Control
Air Governor Control provides continuous running
control in which the air governor responds to air
pressure in the receiver to operate the suction valve
unloaders. If the pressure rises to the set point of
the governor the valve unloaders are operated. The
compressor continues to run, but in the unloaded
condition. When the air pressure in the receiver falls
to the pre-set level the unloaders are released,
allowing the suction valves to close and the
compressor comes on load.
The air governor also operates a valve in the base of
the intercooler to drain accumulated condensate
and relieve interstage pressure.
Refer to Publication C20160-014 for details of the Air
Governor.
5.2 Control Panel
The optional wall-mounted control panel
incorporates a pressure switch, solenoid valve,
runon timer and a solenoid timer. It operates in
conjunction with a separately mounted automatic
contactor type starter for the compressor. The panel
carries a 'HAND/OFF/AUTO' selector switch.
Selector switch in 'HAND' position: The compressor
starts and then runs continuously, responding to
system air demand by unloading at the upper
pressure switch setting and loading at the lower
pressure switch setting.
Selector switch in' AUTO' position: The compressor
starts when receiver pressure is less than the low
setting of the pressure switch. It then runs on load
until receiver pressure reaches the upper setting of
the pressure switch which then operates the
solenoid valve to actuate the unloaders and also
initiates the run-on timer. The compressor continues
to run off-load for the time period set by the run-on
timer. If receiver pressure falls during this period to
the lower setting of the pressure switch, the switch
opens, allowing the solenoid valve to close and the
unloaders to release the suction valves. The
compressor then comes on load.
If receiver pressure does not fall to the lower setting
of the pressure switch during the run-on period the
run-on timer will cause the compressor to be shut
down automatically. It will re-start automatically
when receiver pressure falls sufficiently to operate
the pressure switch.
The unloader solenoid valve in the control panel also
operates the intercooler condensate drain/ pressure
relief valve.
Should the compressor shut down automatically
through the operation of the low oil pressure/high air
temperature safety device it cannot be restarted
until the fault has been rectified and the 'SET RUN/
FAULT RESET' push button on the control panel is
pressed.
Refer to Publication C20160-040 for details of the
Control Panel.
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