
Flooded type water cooled screw chiller (PCB Control)
MCAC-CTSM-2012-11
68
d Discharge the residual refrigerant in the gas system.
e Carry on replacement of the parts of the system.
f After the replacement, extract vacuum in the gas part.
g After the vacuum extraction, keep the negative voltage until the resumed vacuum in the unit meets
the requirements.
h Open the angle valve of liquid system and compressor liquid/air stop valve to ensure the loop of the
entire system is unobstructed.
i Add proper amount of refrigerant, generally 5~10k.
Compressor Oil System
Each compressor/circuit has its own oil system which includes an oil filter, oil solenoid valve, Venturi tube,
oil separator heater, and an oil shut-off valve. A typical oil system is shown in Fig. 34. See Table 33 for oil
charge Quantities.
Fig. 34.
Each screw compressor is connected to a tank (oil separator) separating and collecting the oil from
discharge gas. The discharge gas pressure pushes the oil back into the compressor for compressor seal
and lubrication of all moving parts. During the compression, the oil joints the discharge gas before being
conveyed again into the oil separator and re-start the cycle. The oil flow is granted by the pressure
difference created between the condenser and the evaporator. This difference depends on the cooling
water and evaporator water temperatures. During the start-up it is vital to establish rapidly the
appropriate temperature difference, by checking the right cooling water temperature. The head of
cooling water pump at zero flow rate should not exceed the maximum working pressure of condenser
and plant water side.
Oil recovery system
Each compressor includes a system to recover the oil accumulated inside the evaporator during the
normal operation. This system consists of a jet pump able to collect continuously all the oil from the
evaporator preventing from the accumulation due to the low speed refrigerant gas. The high-pressure
discharge gas feeds the jet pump that creates a depression, which allows the suction of the oil
refrigerant mixture from the evaporator into the compressor to re-establish the oil level inside the
lubrication system. On the oil recovery piping a sight glass allows to check the oil-gas mixture flow to the
compressor. If flow is insufficient or the unit continuously stops for “Low Oil Level” alarm, verify the