Evaporator; Condenser; Fig. 2 - Screw Compressor - York YCAS Installation Operation & Maintenance

Refrigerant gas is drawn into the void created by the
unmeshing of the fi ve 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 press es 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 cy cles overlap, a resulting smooth fl ow 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 pri ma ri ly rolling on a contact band on each of the
rotor's pitch circle. This results in virtually no rotor
wear and in creased reliability, a trademark of the screw
com pres sor.
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
han dle axial loads. Together they maintain accurate rotor
po si tion ing at all pressure ratios, thereby min i miz ing
leak age and maintaining effi ciency. A springless check
valve is installed in the compressor discharge housing
to pre vent compressor rotor backspin due to system
re frig er ant pressure gradients during shut down.
Motor cooling is provided by suction gas from the
evap o ra tor flowing across the motor. Redundant
over load pro tec tion is provided using both thermistor
and cur rent over load protection.
FIG. 2 – SCREW COMPRESSOR
YORK INTERNATIONAL
The compressor is lubricated by removing oil from
the refrigerant using an external oil separator. The
pres sur ized oil from the oil separator is then cooled in
the condenser coils and piped back to the compressor for
lubrication. The com pres sor design working pressure is
450 PSIG (31 bar). Each chill er receives a 300 PSIG (21
bar) low side and a 450 PSIG (31 bar) high side factory
test. A 350 watt (115-1-60) cartridge heat er is located
in the com pres sor. The heat er is tem per a ture activated
to prevent re frig er ant condensation.
The following items are also included:
• An acoustically tuned, internal discharge muffl er to
min i mize noise, while maintaining max i mum fl ow
performance.
• Discharge and suction shutoff valves.
• A rain-tight terminal box.
• A suction gas screen and serviceable, 0.5 - 3.0
micron full fl ow oil fi lter within the compressor
housing.

Evaporator

The system uses a high efficiency Shell and Tube
type Di rect Ex pan sion Evaporator. Each of the 3 or 4
re frig er ant circuits consists of 4 passes with the chilled
liq uid cir cu lat ing back and forth across the tubes from
one end to the other.
The design working pressure of the standard evaporator
on the shell side is 150 PSIG (10 bar), and 350 PSIG (24
bar) for the tube (refrigerant side). The water baffl es
are fab ri cat ed from galvanized steel to resist corrosion.
Re mov able heads are provided for access to internally
en hanced, seamless, copper tubes. Water vent and drain
con nec tions are included.
The evaporator is equipped with a heater for protection
to -20°F (-29°C) ambient and in su lat ed with 3/4" (19
mm) fl exible closed-cell foam.
The water nozzles are provided with grooves for
me chan i cal couplings and should be insulated by the
con trac tor after pipe installation.

Condenser

The fi n and tube condenser coils are manufactured
from seamless, internally enhanced, high condensing
co ef fi cient, corrosion resistant copper tubes arranged in
00485VIP
FORM 201.19-NM6 (804)
2
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