31 - Installation requirements -
6.5.1 Safeguarding against too high pressure
Operating refrigerant pumps against too high pressure (e.g. against partially or fully
closed throttled condition) is not allowed and will damage the refrigerant pump!
A by-pass valve (adjustable) has proven good practice to safeguard the pump against too
high pressure.
To set the by-pass valve select the pressure difference across the pump according table 1 for
the following de-livery head. (take into account the pressure losses in the pipework to the by-
pass valve)
960 RPM 1150 RPM 1450 RPM 1740 RPM
GP 41
11 m 16 m 25 m 36 m
GP 42
20 m 30 m 48 m 70 m
GP 51
13 m 19 m 31 m 47 m
GP 51a
16 m 23 m 37 m 50 m
GP 52
26 m 40 m 65 m -
GP 82
- - 55 m 85 m
A diameter of DN20 has been proven for the by-pass valve.
6.5.2 Dry-run protection
If a minimum level cut out switch is mounted on the separator, it shall be used to switch the
pump off in case of a lack of refrigerant (dry run protection).
6.5.3 Pressure differential switch
A pressure differential switch - with time delay during start up - shall be used when there is
insufficient discharge pressure.
The delay should be set at approx. 30 s, which means if the pump was not able to build up
pressure (e.g. 0,3 – 0,5 bar) within 30 s, the pump will be stopped
This procedure can be repeated a maximum of four times. Then a malfunction message should
be submitted and the pump switched off. After that a restart should only be made after inves-
tigation of the cause of failure and acknowledging the fault indicator.
The pressure differential switch does not protect the pump against too high pressure running
(dead heading)!
6.5.4 Flow switch
A flow switch must be installed, when a bypass valve is not fitted in the refrigerant circuit. It
is known when the bypass valve is not fitted, the pump is capable of producing a differential
pressure without volume flow and has not been stopped by the differential pressure switch.
The flow switch control in the pump discharge shall stop the flow as the flow drops below 0,2
m/s.
See also WITT information sheet W 4652-0.01
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