Daikin WCT Series Operating & Maintenance Manual page 11

Figure 4, Oil & Motor Cooling and Drain Lines
Oil Return Control
Two eductor circuits are provided to properly return oil and refrigerant mixture from the refrigeration
circuits to the oil sump for separation. See Figure 5.
Oil migration is often the result of operating conditions. Small portion of the oil used within the
compressor will be occasionally carried out of the compressor, especially when frequent compressor
start/stop is made. Most of the case oil out of the compressor happens through vent line (see Figure 4) and
will primarily drain to bottom of IGV plenum, and any oil out of the compressor eventually fall or drain to
the evaporator.
The excess accumulation of oil in the evaporator will cause oil-foaming which may entrain liquid
refrigerant into compressor (carry over) and letting compressor performance lower. Also it will cause
evaporator performance down.
For preventing performance loss mentioned in above, Eductor Circuit 1 is equipped for primary oil return,
proactively works preventing oil loss to evaporator. Eductor Circuit 2 works preventing excessive oil
accumulation in the evaporator which helps to maintain good chiller efficiency.
In Eductor Circuit 1, high pressure condenser refrigerant gas flows continuously through the eductor
inducing any low pressure oil accumulated in the inlet guide vane plenum to the oil sump.
OMM WCT
Vent Line
nd
2 Stage
Discharge
Oil Pressure
Centrifugal Chillers
Oil Lubrication
Line
st
1 Stage
nd
Impeller
2 Stage
Impeller
Compressor
Oil Temp
Control
Ref from
Cond
Oil
Filter
Regulator
D-EOMWC01302-16EN - 11/84
st
1 Stage
Suction
Oil
Oil
Cooler
Ref to
Evap