Gardner Denver Reavell 5236, Operating & Maintenance Manual

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P a g e | 3
5236.MK2
COMPRESSOR
V14.0, En
This system comprises a pilot unloader valve, (PUV), and two diaphragm drain valves, (DDV's). The
PUV comprises a three way air valve operated by a solenoid in one direction and a combination of air
and spring pressure in the opposite direction and is automatically actuated by a signal from the motor
starter or a electronic timer. It is of the normally closed mode (compressor unloaded) when de-
energised.
The DDV's are positioned below the crankcase doors mounted on the door of the surge vessel, this
being an integral part of the crankcase, they are piped to the first and second stage separators and
function as unloaders and condensate drain valves.
When the PUV solenoid is energised, first stage air pressure activates flexible diaphragms within the
DDV's which forces the valve onto their seats, thus bringing the compressor onto load. When the PUV
solenoid is de-energised the first stage is released to atmosphere via the PUV exhaust port and air
pressure from both the compressor separators forces the DDV's open allowing condensate to drain
from the separators and the compressor to run in an unloaded condition. The system is designed so
that the DDV's are open during starting, for condensate draining whilst running on load and on
shutdown.
It is essential that a timer is fitted in the unloading circuit to provide a timed drainage facility to prevent
accumulation of condensate. Time between drainage cycles should be set to a 30 minute period with
an approximate 5/6 second duration to clear condensates from the separators.
1.9 SUCTION UNLOADING
The unloading of the suction valves during compressor start-up is necessary to reduce starting torque
and prevent motor overload.
This system comprises a PUV and two first stage suction unloaders. The PUV comprises a three-way
air valve operated by a solenoid in one direction and a combination of air and spring pressure in the
opposite direction this is automatically actuated by a signal from the starter/control panel. It is of the
normally open mode (compressor unloaded) when de-energised.
The first stage suction unloaders are positioned on the first valve covers and are used to automatically
unload the compressor during starting and when running unloaded.
When the PUV solenoid is de-energised , second stage (i.e. receiver) air pressure forces the unloader
piston down to unload the first stage suction valve until the solenoid is re-energised, bring the
compressor on to load.
The suction unloaders can also be used manually, by means of the hand operated knobs.
Manual operation is necessary when the system pressure is lower than 10 barg. Lower system
pressures may prevent correct operation of unloaders and cause motor overload.
To operate by hand, screw down knobs fully in a clockwise direction, this moves the push rod which
operates the valve unloader fork to hold the suction valve plate off its seat thus allowing air to flow
freely in and out of the compressor cylinder without compressing the air.