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 ft
3
/min. 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(0.71~1.06 ft
3
/min) usually take an extremely
long time to achieve vacuum. (We recommend a vacuum pump of approx. 60~100
ℓ
/min(2.12~3.53 ft
3
/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, Pascal(Pa), and psi. 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
760
0
hPa
hPa
1013.33
0
psi
psi
14.70
0
Degree of vacuum must be within the range expressed by
0 Torr
0 hPa
0 mmHg
0 psi
6.67 hPa
5 mmHg
0.096 psi
1013.33 hPa
760 mmHg
14.70 psi
Perfect vacuum
5 Torr
Vacuum target value
760 Torr
Standard atmospheric pressure
2. Guideline for each installation process
32
_
Heat pump 60Hz/R410A
Installation of
Outdoor Units
SINGLE ZONE
