Daikin VRV II Series Design, Installation & Testing Instructions page 38

Installation
Choosing a
General
Refrigerant piping content volume of the VRVII R410A Series is larger than the VRV Inverter Series, and
Vacuum Pump
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).
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, and the vacuum pump oil may flow back. Moreover, if the vacuum pump stops during the
operation by some reason, the same thing happens.
In such cases, different oil mixes in the HFC system refrigerant apparatus cycle, and becomes the cause of
a refrigerant circuit trouble. Therefore, in order to prevent the counter flow from the vacuum pump, a check
valve is needed.
Vacuum pump with check valve or vacuum pump adapter
1. Vacuum pump performance
(1) Exhaust velocity
(2) Degree of vacuum
Gauge Pressure
Absolute Pressure
Torr
Micron
∗ mmHg
Pa
Degree of vacuum must be within the range expressed by
0 Torr
0 Pa
760 mmHg
Perfect vacuum
32
Vacuum pump with
check valve
The 2 most import things for determining vacuum pump performance are as follows:
(1) Exhaust velocity
(2) Degree of vacuum
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.)
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
kg/cm2
kg/cm2 abs
Torr
Micron
mmHg
hPa
5 Torr
667 Pa
755 mmHg
Vacuum target value
Vacuum pump adapter
Reverse flow preventive
vacuum adapter
Standard atmospheric pressure
0
1.033
760
760000
0
1013.33
Si39-303
Perfect vacuum
–1.033
0
0
0
760
0
760 Torr
1013.33 hPa
0 mmHg
Standard atmospheric pressure
(V0992)
General Information