Flooded type water cooled screw chiller (PCB Control)
102
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
correct operation of the corresponding circuit.
Oil Charging/Low Oil Recharging
Pre-cautions in changing of oil
1.
Use only qualified oil and do not mix different brand of oil together. Different kinds of refrigerant should
match different kinds of oil, note that some synthetic oil is incompatible with mineral oil.
2. When using the synthetic oil for the chiller system, be sure not to expose the oil to atmosphere for a
long time, it is also necessary to vacuum the system completely when installing the compressor.
3. In order to ensure no moisture inside the system, it is suggested to clean the system by charging it
with dry Nitrogen and then vacuum the system repeatedly as long as possible.
4. It is essential to change for new oil especially after the motor burns out; the acidity debris still remain
inside the system so clean work must be done to overhaul the system. Check the oil acidity after 72
hours of operation and then change it again until the oil acidity is in the standard value.
5. Contact local distributor/agent for concerning unqualified oil to be used.
