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Section II – Description
Water-cooled Fluid Coolers
Water-cooled fluid coolers are of the shell and tube design. Fluid passes through the shell transferring
its heat to the water flowing through the tubes. Fluid leaving the cooler does not pass through a
thermal mixing valve as in an air-cooled unit, but goes directly to the fluid filter and the compressor.
Fluid discharge temperature at the compressor is maintained by a water temperature regulating valve
located in the discharge water line. The water temperature-regulating valve uses a probe to sense fluid
temperature and opens and closes, governing water flow through the cooler.
Aftercoolers
Air-cooled aftercoolers are furnished as standard equipment on the QSF. Water-cooled aftercoolers are
available as an option on standard QSF. Aftercoolers are used to lower the temperature of the
discharge air, thereby condensing water vapor from the compressed air. This allows most of the
contained water to be trapped and expelled from the unit, reducing water related problems
downstream.
Air-cooled aftercoolers are part of the air-cooled fluid cooler. Cooling air from the fan is blown through
the aftercooler and the fluid cooler.
Water-cooled aftercoolers are placed in series with the fluid cooler. Incoming water is first directed
through the aftercooler and then on to the fluid cooler.
A combination moisture separator and water trap is provided for collecting and expelling water to the
customer's drain.
Modulation Control Standard
As the motor starts driving the compressor rotors, air is drawn in, compressed and discharged into the
reservoir. When the air pressure in the 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. 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 transducer 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. See control
schematic in parts manual.
Auto/Dual Standard
The Auto/Dual system is standard on the Quincy QSF Compressor.
The control uses a programmable timer to shut the compressor down if it stays unloaded for the
programmed time period. 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 electronic control to load
the compressor, the timer will reset.
Quincy Compressor – QSF Series
7
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