- Applications - 24
APPLICATIONS
5.1 GENERAL
In industrial refrigeration systems pumps are used to deliver refrigerant to the evaporators.
WITT refrigerant pumps are designed especially for this purpose.
The principle of a pump re-circulation system is shown in fig. 4.
Fig. 4 principle of pump recirculation system
WITT refrigerant pumps differ from conventional centrifu-gal pump designs due to the fact that
large volumes of entrained vapour (gas bubbles) do not completely stop delivery of the refrig-
erant liquid. Large volumes of gas occur in the pump suction when the evaporation tempera-
ture of the plant fluctuates during the production cycle, particularly during compressor start up
(pull down period) and during the rapid loading or unloading of compressor steps of capacity.
Large amounts of gas bubbles in the pump suction line will cause the mass flow of liquid re-
frigerant to be re-duced.
It is important to ensure the pump suction lines are sized generously.
With respect to the lifetime of the shaft seals the pump should only be operated in the pressure
range below 10 bar (145 psi) in continuous operation. If higher pres-sures are expected, this
should be specified when ordering.
Long periods of cavitation must be avoided, as this will cause premature failure of
the pump. It is im-portant the installation instructions in chapter. 6 are correctly
understood and followed.
A horizontal separator is recommended: this gives great-er surface area for the settlement of
any oil and stable suction head conditions.
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