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Product Description
Refrigerant gas is injected into the void created by the
unmeshing of the five-lobed male and seven-lobed fe-
male rotors. Further meshing of the rotors closes the
rotor threads to the suction port and progressively com-
presses the gas in an axial direction to the discharge
port. The gas is compressed in volume and increased in
pressure before exiting at a designed volume at the dis-
charge end of the rotor casing. Since the intake and dis-
charge cycles overlap, a resulting smooth flow of gas is
maintained.
The rotors are housed in a cast iron compressor hous-
ing precision machined to provide optimal clearances
for the rotors. Contact between the male and female
rotors is primarily rolling on a contact band on each of
the rotor's pitch circle. This results in virtually no rotor
wear and increased reliability, a trademark of the screw
compressor.
The compressor incorporates a complete anti-friction
bearing design for reduced power input and increased
reliability. Four separated, cylindrical, roller bearings
handle radial loads. Angular-contact ball bearings
handle axial loads. Together they maintain accurate
rotor positioning at all pressure ratios, thereby mini-
mizing leakage and maintaining efficiency. A springless
check valve is installed in the compressor discharge
housing to prevent compressor rotor backspin due to
system refrigerant pressure gradients during shutdown.
Motor cooling is provided by suction gas from the
evaporator flowing across the motor. Redundant over-
load protection is provided using both thermistor and
current overload protection.
FIG. 2 – SCREW COMPRESSOR
16
The compressor is lubricated by removing oil from the
refrigerant using an external oil separator. The pressur-
ized oil is then cooled in the condenser coils and piped
back to the compressor for lubrication. The compres-
sor design working pressure is 31 bar (450 PSIG). Each
chiller receives a 21 bar (300 PSIG) low-side and a 31
bar (450 PSIG) high-side factory test. A 350 watt
(115-1-50) cartridge heater is located in the compres-
sor. The heater is temperature-activated to prevent re-
frigerant condensation.
The following items are also included:
• An acoustically tuned, internal discharge muffler
to minimize noise, while operating flow for maxi-
mum performance.
• Discharge and suction shutoff valves.
• A rain-tight terminal box.
• A suction gas screen and serviceable, 0.5 micron
full-flow oil filter within the compressor housing.
Cooler
The system uses a Shell-and-Tube, Direct Expansion
Evaporator. Each of the refrigerant circuits consists of
4 passes with the chilled liquid circulating back and
forth across the tubes from one end to the other.
The design working pressure of the cooler on the shell
side is 10 bar (150 PSIG), and 21 bar (300 PSIG) for
the tube (refrigerant side). The water baffles are fabri-
cated from galvanized steel to resist corrosion. Remov-
able heads are provided for access to internally en-
hanced, seamless, copper tubes. Water vent and drain
connections are included.
The cooler is equipped with a thermostatically con-
trolled heater for protection to -29°C (-20°F) ambient
and insulated with flexible closed-cell foam.
The water nozzles are provided with grooves for me-
chanical couplings and should be insulated by the con-
tractor after pipe installation.
Condenser
The fin-and-tube condenser coils are manufactured from
seamless, internally enhanced, high condensing coeffi-
cient, corrosion-resistant copper tubes arranged in stag-
gered rows and mechanically expanded into corrosion-
resistant aluminum alloy fins with full-height fin col-
lars. They have a design working pressure of 31 bar
00485VIP
(450 PSIG).
YORK INTERNATIONAL
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