Quincy Compressor QSB Series, Instruction Manual

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Section II - Description
8
Quincy Compressor ® - QSB/T ™
Capacity Control System
As the motor starts driving the compressor rotors, air is
drawn in, compressed and discharged into the air/fluid
reservoir. When the air pressure in the air/fluid reservoir
exceeds the set point of the pilot valve (normally 100
PSIG), the valve opens and passes a controlled volume of
air to the inlet valve air cylinder.
NOTICE!
Other pressures are available optionally.
The air forces a piston to move within the cylinder,
closing the inlet valve. The compressor will continue to
run, matching air demand with air delivery by constantly
adjusting the position of the inlet valve. The inlet valve
regulates compressor capacity between 100% and nearly
0% of rated delivery.
When maximum pressure (typically 10 PSIG above
normal full load pressure) has been obtained in the air
system, complete compressor unloading occurs. The
pressure switch located in the control panel sends a signal
to the control and the solenoid valve opens, venting the
residual pressure from the blowdown valve. At the same
time, control air from the reservoir check valve is directed
through the solenoid to the inlet valve air cylinder. The
inlet valve is held in a closed position preventing the
intake of air into the compressor and serving as a check
valve preventing reverse air/fluid flow through the inlet
valve and air filter.
Auto Dual (Standard)
The Auto Dual system offers two choices of controlling
the Quincy QSB/T
™ Compressor:
With the selector switch in the Continuous Run position,
the compressor operates continuously, matching air
demand as the differential pilot valve controls the position
of the inlet valve. When maximum system pressure is
reached, the pressure switch opens, venting the air/fluid
reservoir and, although the compressor continues to run
unloaded, no air is compressed.
When Auto Dual is selected, the compressor will perform
as above, however, a solid state timer is activated when
the pressure switch contacts open. This timer is
adjustable within a ten (10) minute range. When the timer
reaches the end of its delay period, the compressor will
automatically shut down and assume a standby mode.
Upon a drop in system air pressure, the pressure switch
contacts close, restarting the compressor automatically.
The timer should be set, during unit start-up, for a
minimum of six (6) minutes.
During the unloaded/timing mode, if plant pressure
should drop causing the pressure switch contacts to close,
the compressor will continue to operate, resetting the
timer and instructing the inlet valve to reopen.