Hot water pump

The hot water pump is a centrifugal pump for handling water at temperatures above 100 ºC. They are used for boiler feeding (see Boiler feed pump), central heating (see Circulator pump) and feed water circulation, and also as circulating pumps in nuclear plants (see Reactor pump). 

Materials frequently used for hot water pumps are cast iron, nodular cast iron, cast steel, cast chrome steel and austenitic cast steel as well as appropriate wrought alloys for specific pump casings. 

In the event of sudden temperature changes, considerable stresses act in the tie bolts of ring-section pumps and in the barrels of barrel pull-out pumps.

In order to prevent any shifting of the pump and motor shaft centrelines towards one another under the influence of the high casing temperature, the pump feet are usually arranged at shaft centreline height on the pump casing. This pump foot arrangement is characteristic of hot water pumps in ring-section design. 

See Fig. 1 Hot water pump

In single-stage hot water pumps, the feet are very often also arranged at the bottom of the pump casing. 

See Fig. 2 Hot water pump

To compensate for unavoidable shaft displacement, double Cardan couplings are used (see Shaft coupling). These offer a reliable alternative to pump casings with feet at the centreline.

Depending on temperature and pressure conditions, the casing is sealed (see Sealing element) by O-rings, spiral-wound gaskets or flat gaskets. 

The shaft seal must operate at a low temperature level. For this reason, frictional heat is dissipated. This is done either by means of an external coolant which supplies the shaft seal chamber or heat exchanger, or may alternatively be effected by environmentally friendly air cooling.

See Fig. 2 Hot water pump

Mechanical seals or occasionally even gland packings or floating ring seals can be used as types of seal (see Shaft seal). 

The shaft itself runs in oil-lubricated rolling element or plain bearings cooled by air, oil or water.