4-6
4.2 Precautions for Operation
4.2.1 Prevention of Liquid Flow-back
Liquid flow-back is a phenomenon where refrigerant that did not completely evaporate with the gas
reaches the compressor. Liquid flow-back may cause insufficient lubrication of the compressor,
abnormal vibrations and noises, and abnormal foaming of lubricating oil (too much oil loss). To prevent
liquid flow-back, properly adjust the expansion valve of each liquid cooler.
For details, refer to "Troubleshooting" in this manual C.
4.2.2 Purging of Non-Condensable Gases
Some types of refrigerants emit bad smells or toxic gases. Make sure to ventilate
the air during work.
If there is a leak on the low-pressure side of the refrigeration cycle, air may enter the package unit.
If non-condensable gas like air enters the unit, the condensing pressure rises and the energy
consumption increases. This leads to uneconomical operation.
Follow the procedure below to check for non-condensable gases.
1. When the compressor is stopped, allow the cooling water to flow to the condenser for at least 15
minutes. Check the condensing pressure by using the pressure gauge of the compressor.
2. Check the cooling water temperature.
3. Compare the condensing pressure checked in step 1 above with the refrigerant saturation pressure
that depends on the cooling water temperature (as shown in Table 4-3).
4. When the pressure inside the condenser and the refrigerant saturation pressure that depends on the
cooling water temperature are approximately equivalent, non-condensable gases do not exist.
When the pressure inside the condenser is 0.05 MPa or more higher than the refrigerant saturation
pressure that depends on the cooling water temperature, there is a possibility of non-condensable
gases entering the unit. In that case, purge the non-condensable gases from the condenser.
Table 4-3
Typical Refrigerant Temperature and Saturation Pressure
Temperature °C
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