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Refrigerant gas is injected into the void created by the
unmeshing of the five lobed male and seven lobed fe-
male rotor. Further meshing of the rotors closes the ro-
tor 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
rotor 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
YORK INTERNATIONAL
The compressor is lubricated by removing oil from the
refrigerant using an external oil separator. The pres-
surized oil is then cooled in the condenser coils and
piped back to the compressor for lubrication. The com-
pressor 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:
• Internal discharge check valve to prevent rotor back-
spin or shutdown.
• 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.
Evaporator
The system uses a high efficiency Shell and Tube type
Direct Expansion Evaporator. Each of the 2 refriger-
ant 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 24 bar (350 PSIG) for
the tube (refrigerant side). The water baffles are fabri-
cated from galvanized steel to resist corrosion. Re-
movable 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 19 mm (3/4") 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-
LD03674
FORM 201.18-NM6
2
13
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