15
unit unloads via Suction Valve Unloading, this item
is included. Located on the inlet valve covers, the
tower provides the mechanical motion (pneumatically
driven via a diaphragm) to physically open the inlet
valve(s). 1, 2 or 4 towers are employed depending
upon the model of compressor. This tower must be
supplied with gas pressure to operate the suction valve
unloaders. The unloader gas pressure must exceed
the inlet pressure by a minimum of 30 psig in order for
the unloader mechanism to operate effectively. If the
unit comes with an unloading valve of some type, the
plumbing from the valve to the towers is done at the
factory. If no unloading valve device is present, use a
minimum of 1/4” tube of appropriate pressure rating, to
supply unloading gas/air to the unloader towers.
Hydraulic Unloader Valve – Provided on all pressure
lubricated Hycomp model ambient air compressors and
some air boosters and gas compressors. Located at
Figure 9: Constant Speed Unloader (Pilot
Valve)
Constant Speed
Unloader Valve (Pilot
Valve)
Connect to Unloader
Towers or 3-Way
Check Valve
Connect to Air
Receiver
the top of the oil pump housing, this unloader valve
senses oil pressure and supplies unloading pressure
to the unloading towers, when there is not suffi cient oil
pressure (see Figures 7 and 8). When the oil pressure
rises, the hydraulic unloader valve vents the unloader
pressure to atmosphere. This provides protection to
the compressor in the event of a potentially damaging
oil pressure drop. It also insures the compressor will
not begin compression until oil pressure has risen to
an acceptable level. THIS VALVE IS ONLY TO BE
USED WHEN THE UNLOADER GAS IS AIR OR A
NON-CONTAMINATING GAS THAT CAN BE SAFELY
RELEASED TO THE LOCAL ENVIRONMENT.
Constant Speed Unloader (Pilot Valve) – Provided
upon request for any Hycomp model air compressor.
Not used on air boosters or gas compressors. Located
on the side of the oil pump housing, this unloader
valve senses discharge receiver pressure and sends
pressure to the unloader towers when the receiver
pressure is adequate. When receiver pressure falls
below the required pressure, the pilot valve vents
the unloader pressure to atmosphere. Connect the
inlet to the discharge air receiver, and the outlet to
the unloader towers or a three way check valve. The
pilot valve is used when an air compressor is to run
continuously and a minimum operating pressure is to
be maintained. The pilot valve is not used on air or
gas booster compressors. THIS VALVE IS ONLY TO
BE USED WHEN THE UNLOADER GAS IS AIR OR A
NON-CONTAMINATING GAS THAT CAN BE SAFELY
RELEASED TO THE LOCAL ENVIRONMENT.
Figure 10: Dual Control - Constant Speed Unloader and Hydraulic Unloader
To Unloader
Towers
To Air
Receiver
Constant Speed
Unloader Valve
Hydraulic Unloader Valve
(installed in Oil Pump
which is not shown)
Unloader Towers
3-Way Check
Valve
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