Technical data

The rotors are manufactured from forged steel and use
asymmetric profiles. The compressor incorporates a
complete anti-friction bearing design for reduced power
and increased reliability. Four separate cylindrical roller
bearings handle radial loads. Two 4-point angular
contact ball bearings handle axial loads. Together they
maintain accurate rotor positioning at all pressure ratios
thereby minimising blow-by and maintaining efficiency.
Oil is injected into the compressor by differential
pressure to lubricate the bearings, seal the rotors and
remove the heat of compression. The injected oil mixes
with the compressed gas and is separated from the
refrigerant gas in the oil separator.
The compressor has an oil reservoir located at the rotor
bearings to provide lubrication during start-up and
during coast-down even in the event of a power failure.
A check valve is installed in the compressor discharge
housing (suction housing for S4 and S5 compressors) to
prevent reverse running of the rotors due to system
refrigerant pressure gradients during shutdown.
The open-drive compressor shaft seal consists of a
spring-loaded, precision carbon ring, high temperature
elastomer "0" ring static seal, and stress-relieved,
precision lapped collars. The entire shaft seal cavity is at
low pressure, being vented to the oil drain from the
compressor, combining low pressure with direct oil
cooling for long seal life.
Capacity control is achieved by use of a slide valve
providing fully modulating capacity control from 10% to
100% of full load. The slide valve is positioned between
the male and female rotors and moves axially to match
the compressor capacity to that of the evaporator
refrigeration load. As the slide valve moves toward the
unloaded position, less suction gas is pumped through
the compressor.
The slide valve is actuated by oil pressure controlled by
external solenoid valves via the control centre. When
the compressor is shut off, a spring returns the slide
valve to unloaded position to ensure that the
compressor starts with the slide valve in the unloaded
position.
2-2 035L02381-GB0
MOTOR
TERMINAL BOX
RELIEF
VALVE
RELIEF
VALVE
CONDENSER
LIQUID LINE
ISOLATION VALVE
ISOLATION
VALVE
COOLER
OIL
SEPARATOR
Figure 2.2 YS Centrifugal Liquid Chiller (Rear View)