Installation SiE33-102
30 General Information
Choosing a
Vacuum Pump
General
Refrigerant piping content volume of the Plus Series is larger than the VRV Inverter Series, and
consequently takes more time for vacuum drying. If you have time to spare, you may use the same vacuum
pump, but if you want to save time, you will have to use a pump with higher exhaust velocity (exhaust
volume).
1. Vacuum pump performance
The 2 most import 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 m³/h. The larger the number, the faster vacuum id
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, nnHg, and Pascal (Pa). The units correlate as follows:
Unit Standard atmospheric pressure Perfect vacuum
Gauge Pressure kg/cm² 0 –1.033
Absolute Pressure kg/cm² abs 1.033 0
Torr Torr 760 0
Micron Micron 760000 0
cmHg cmHg 0 76
Pa hPa 1013.33 0
Degree of vacuum must be within the range expressed by
0 Torr
0 Pa
76 cmHg
Perfect vacuum
5 Torr
667 Pa
75.5 cmHg
Vacuum target value
760 Torr
1013.33 hPa
0 cmHg
Standard atmospheric pressure
(V0992)
Si33-102.book Page 30 Tuesday, June 26, 2001 3:18 PM
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