3.1. General industrial pumps.
Centrifugal overhung pumps are mainly used for circulation of water (for condenser cooling) and intermediate cooling medium. Domestic and foreign companies offer a wide range of such pumps with a flow rate from 5 to 400 m3/h and a head from 5 to 125 m. The external view of pumping assembly of the given type is presented in fig. 3.1.
Fig. 3.1. The centrifugal overhung pump of “K” type. External view.
To raise the system reliable performance the pumping machinery should be a subject to redundancy. Standby pumps are brought into the diagram along with the main ones, and isolation valves for pumps switching-over are installed on pipelines.
3.2. Special leakproof pumps.
Special leakproof pumps are applied for liquid ammonia pumping in pump circulating circuits of refrigeration units. Pumps construction avoids the refrigerant leak. Integrated motor elements are separated from a pumped fluid with thin-wall (0.5 mm) liners. Motor cooling and bearings lubrication are performed by the pumped fluid. Pumps serial production of this type for ammonia refrigeration units was commercialized at Kishinev factory of leakproof pumps “CRIS” SRL. The external view of leakproof ammonia pump is presented in fig. 3.2.
Fig. 3.2. The electric pump unit of “ЦГ/TSG” type. External view.
Centrifugal ammonia pumps must have the liquid boosting not less than 1.5 m, which prevents boiling-up of liquid ammonia upstream of the pump (cavitation effect). To make boosting the pump intake branch pipe should be lower than the minimum possible level in a circulating receiver by the given value and the hydraulic resistance of suction line should be minimal.