SiE33-102 Installation
General Information 29
3.2.6 Vacuum Drying
What is vacuum
drying?
Vacuum drying is:
“The use of a vacuum pump to vaporize (gasify) the moisture (liquid) inside the pipes and expel it leaving
the pipes completely dry inside.”
At 1 atm (760 mmHg) the boiling point (evaporating temperature) of water is 100˚C but if a vacuum is
created inside the pipes using a vacuum pump then the boiling point is rapidly reduced as the degree of the
vacuum is increased. If the boiling point is reduced to a level below that of the ambient temperature then
the moisture in the pipes will evaporate.
The evacuation of air conditioner piping provides the following effects.
1. Vacuum drying
2. Removes air and nitrogen (used in air-tightness test) from the inside of pipes.
Therfore, it is necessary to ensure that the both purposes have been achieved in the vacuum drying
operation.
<Example>
When outside temperature is 72˚C
As shown in the table on the right, the degree
of vacuum must be lowered below –75.2cmHg.
Boiling point
of water (˚C)
Pressure
∗cmHg Pa Torr
40 –70.5 7333 55
30 –72.4 4800 36
26.7 –73.5 3333 25
24.4 –73.8 3066 22
22.2 –74.0 2666 20
20.6 –74.2 2400 18
17.8 –74.5 2000 15
15.0 –74.7 1733 13
11.7 –75.0 1333 10
→ 7.2 –75.2 1066 8
0 –75.5 667 5
Above figures (cmHg) are gauge pressure readings.
Key points
Lower the degree of vacuum to below –755mmHg
(V1216)
Si33-102.book Page 29 Tuesday, June 26, 2001 3:18 PM
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