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Section II – Description
The Compression Cycle
The compression cycle of a rotary compressor is a continuous process from intake to discharge with no
reciprocating mechanisms starting and stopping as found in reciprocating compressors. The compressor
consists of two rotors in constant mesh, housed in a cylinder with two parallel adjoining bores. The male
drive rotor has four lobes that mesh with six flutes in the female rotor. All parts are machined to exacting
tolerances.
As the rotors rotate, (male-clockwise as viewed from the power-input end) air is drawn into the cylinder
through the inlet port located at the power-input end. A volume of air is trapped as the rotor lobes pass
the inlet cut off points in the cylinders. Compression occurs as the male rotor rolls into the female flute,
progressively reducing the space thereby raising the pressure. Compression continues until the lobe
and flute pass the discharge port. The compressed air is then discharged into the service line. There are
four complete compression cycles for each complete rotation of the male rotor. (Figure 2-1).
Description of Air Flow
With the compressor operating, air entering via the compressor air filter flows directly into the rotor
housing where it is compressed. Compressed air passes through the complete system then through a
minimum pressure check valve to the service connection.
Description of Fluid Flow and Compressor Cooling System
The fluid serves three functions: it lubricates the bearings, rotors, and gears; it removes heat from the air
as the air is being compressed thus lowering the compressed air discharge temperature; it also seals the
rotor clearances.
Coolers
All models use positive pressure in the reservoir to circulate fluid. Fluid is circulated through the cooler,
fluid filter, and into the compressor. In the compressor, some fluid is diverted directly through internal
passages to ensure positive lubrication of the bearings, gears and shaft seal. The remainder of the fluid
is injected into the early stage of the compression cycle to seal clearances, cool, and lubricate the rotors.
Fluid Coolers
Fluid coolers may use either air or water as a cooling medium. The following descriptions point out the
major differences between the two types of coolers.
Air-cooled Fluid Coolers
The air-cooled fluid cooler and aftercooler are of the finned aluminum tube design. Ambient air is
forced through the fins by a motor driven fan, cooling the fluid and air in the tubes. To maintain proper
compressor operation, the temperature of the ambient air should not exceed the temperatures listed in
the QSF specifications. The cooler fins must be kept clean at all times. Fluid leaving the receiver passes
through a thermal mixing valve before traveling on to the cooler. The purpose of the thermal valve is to
maintain a minimum fluid discharge temperature at the compressor of approximately 180
6
Quincy Compressor – QSF Series
0
Fahrenheit.
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