Flexible Impeller Pumps

Flexible impeller pumps are of the positive displacement type with the impeller made of an elasto- mer. The impeller consists of a number of radial flexible vanes the outer diameter of which is larger than the inner diameter of the pump casing, so that the tips of the vanes are bent thus staying in close contact with the casing. As the impeller turns a cam between inlet and outlet port serves as a restriction which bends the vane passing by somewhat more so that part of the trapped liquid is squeezed out into the discharge line. Having passed the cam the vane opens up again and admits liquid from the suction line.

Flexible impeller pumps have excellent self-priming capability due to the close contact between the rubber impeller and the casing. On the other hand they are very sensitive to lack of liquid (dry running) which may damage the impeller after just a few seconds up to some minutes depending on pump quality. The high friction of the impeller in the casing means an important loss of energy, which is not available for transport of the liquid to be pumped.

Flexible impeller pumps are mostly used for cooling water on board of ships. In sanitary design, however, they are also used for foodstuff and beverages, because their self-priming capability reduces hygienically critical orifices in the system and the gentle pumping action does less harm to the products than centrifugal pumps (milk).

(taken from Wikipedia)

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