Air Source Screw Water Chiller Unit – Installation Operation and Maintenance Manual
35
Note: The vacuum drying procedure must be strictly performed for all systems. Otherwise, ice plug
will occur.
(1) Procedure for common vacuum drying
①
Vacuum drying (the first time): Connect the pressure measuring set to the stop valve of the liquid
pipe and gas pipe. Then, start the vacuum pump and keep it running for over two hours. (The
vacuum degree should be lower than –756 mmHg.)
②
If the vacuum degree cannot reach a value lower than –756 mmHg after two-hours' pumping, it
indicates that water or leak source exits in the pipe system. In this case, keep pumping for another
one hour.
③
If the vacuum degree cannot reach a value lower than –756 mmHg after three-hours' pumping,
check for leak sources.
④
Perform pumping from the directions of both the liquid pipe and gas pipe.
⑤
Vacuum stability test can be performed when the vacuum degree reaches –756 mmHg. If the
hand of the vacuum gauge does not point to a larger value after one hour, it indicates that no water or
leak source exists. If the hand of the vacuum gauge points to a larger value after one hour, it
indicates that water or leak source exists.
Note: It is forbidden to remove the pressure gauge during vacuum pressure maintaining
process. Otherwise, external air will be taken in.
(2) Procedure for special vacuum drying
Special vacuum drying is applicable to the following scenarios:
①
Water is detected during the blowing and cleaning of refrigerant pipe.
②
Rain water may enter the pipe in the rainy season.
③
Rain water may remain in the pipe since the pipe is not checked for a long time.
④
Rain water may enter the pipe during construction.
The procedure for special vacuum drying is as follows:
a. Vacuum drying (the first time): Keep the pump running for two hours.
b. Vacuum breaking (the first time): Fill nitrogen into the pipe. The pressure is 0.5 kgf/cm
2
.
Dry nitrogen can dry out the inner part of pipe. However, the inner part of pipe cannot be thoroughly
dried out by using this method if too much water exists. Therefore, avoid water inflow and
condensate water during refrigerant piping.
c. Vacuum drying (the second time): Keep the pump running for one hour.
Determining the result: When the vacuum degree is lower than –756 mmHg, the test is passed. If the
vacuum degree cannot be lower than –756 mmHg after two-hours' pumping, repeat step b and step c.
Note: Maintain system pressure after vacuum drying is completed. Keep the pipe in vacuum for one
hour. If the pressure does not rebound, the test is passed.
