2. Guideline for each installation process
31 _
Heat pump
60Hz/R410A
Part 3 Design and installation
2.7.3 Choosing a vacuum pump
The necessity for counter flow prevention
After the vacuum process of the refrigerant cycle, the inside of the hose will be vacuumed after stopping the vacuum pump,
the oil of vacuumpump may flow back. Moreover, if the vacuum pump stops during the operation for some reason.
Therefore, in order to prevent the counter flow from the vacuum pump, a check valve is reguired.
1) Vacuum pump performance
The 2 most important things for determining vacuum pump performance are as follows:
① Exhaust velocity
② Degree of vacuum
①
Exhaust velocity
Exhaust volume is usually expressed as l/min or m
3
/hr. The larger the number, the faster the vacuum is achieved.
Generally speaking, the faster the exhaust velocity, the larger and heavier the vacuum pump itself is.
Commercially available vacuum pumps (exhaust velocity of 20 - 30 l/min) usually take an extremely long time to achieve
vacuum. (We recommend a vacuum pump of approx. 60 - 100 l/min.)
②
Degree of vacuum
Ultimate vacuum varies largely according to use of the vacuum pump. Vacuum pumps used for vacuum forming cannot be
used for vacuum drying. (A vacuum pump with a high degree of vacuum is required.)
When selecting a vacuum, you should select one which is capable of achieving 0.2 Torr of ultimate vacuum.
Degree of vacuum is expressed in Torr, micron, mmHg, and Pascal (Pa). The units correlate as follows:
Unit Standard atmospheric pressure Perfect vacuum
Gauge pressure kg/cm
2
0 -1.033
Absolute pressure kg/cm
2
abs 1.033 0
Torr Torr 760 0
Micron Micron 760000 0
mmHg mmHg 0 760
Pa Pa 1013.33 0
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