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Figure 22, Vane Control Solenoid Operation, Continued
Surge and Stall
Stall and surge are a characteristic of all centrifugal compressors. These conditions occur when low load combines
with high compressor lift. In a stall, discharge gas has insufficient velocity leaving the impeller to reach the volute
and just “sits” or stalls in the diffuser section. The compressor sound level goes way down due to no flow and the
impeller starts to heat up. In surge, the heated discharge gas alternately flows back through the impeller and then
reverses to the volute about every two seconds. Extreme noise and vibration occur. The compressor is equipped
with a temperature sensor that shuts it off if these conditions occur.
Lubrication System
The lubrication system provides lubrication and heat removal for compressor bearings and internal parts. In addition,
the system provides lubricant under pressure to hydraulically operate the unloading piston for positioning the inlet
guide vanes for capacity control. DWDC, dual compressor chillers, have completely independent lubrication systems
for each compressor.
Only the recommended lubricant, as shown in Table 13, can be used for proper operation of the hydraulic system
and bearing lubrication system. Each unit is factory-charged with the correct amount of the recommended lubricant.
Under normal operation, no additional lubricant is needed. Lubricant must be visible in the sump sight glass at all
times.
The compressor sizes, CE079, through CE126, utilize a separate lubricant pump located in the sump. The sump
includes the pump, motor, heater and lubricant/vapor separator system. The lubricant is pumped through the external
oil cooler and then to the oil filter located inside the compressor housing. DWSC/DWDC/DWCC 063-126 units,
single or dual compressor, all utilize a water-cooled oil cooler for each compressor.
Drain From Piston
#3 Outlet
SB
SA
#1 Intlet
LEGEND
Oil Under Pressure
To Oil
Pump Sump
Section “SB”
Energized
Section “SA”
De-energized
From Oil
Pump Discharge
OPENING
Oil Sump Pressure
Drain From Piston
#3 Outlet
SB
SA
#1 Intlet
To Oil
Pump Sump
Section “SB”
De-energized
Section “SA”
Energized
From Oil
Pump Discharge
CLOSING
Piston Drain
