Various attempts have been made to overcome the need for frequent replacement of the wear plate in open-impeller pumps. For example, the wear plate may be faced with hard tool steel. Although, the steel resists wear, it is so hard that it must be ground to produce a flat, even surface. This makes the manufacture of such wear plates expensive.

Alternatively, the edge of the wear plate around the inlet opening may be faced with a high-quality hard-wearing rubber. Although this is relatively cheap, rubber-faced wear-plates last only slightly longer than conventional wear plates of plastics or synthetic rubber. In tests in which a centrifugal pump of known type was operated continuously to draw a slurry of sand-gravel and water to a height of fifteen feet, the self-priming ability of the pump was tested at intervals. A pump having a conventional wear plate of hard plastics material (polyurethane) became unable to draw water into the pump when re-started after a period of 41/2 hours.Water Control valves A pump with a high quality Buna-N type rubber-faced wear plate lost its ability to draw water to a height of fifteen feet after 91/2 hours.

In some existing forms of closed impeller pumps, a seal is formed between two closely-spaced cylindrical surfaces, one surface being provided on the inlet to the impeller and the other being provided on a sleeve integral with the casing and surrounding the inlet. However, when such pumps are used to pump gritty slurries, there is a tendency for abrasive particles to become trapped in the seal and, because the radius of the seal is relatively small, the centrifugal force at the seal is insufficient to throw the particles clear of the seal.FORGED STEEL VALVES Further, as the interface between the surfaces extends parallel to the axis of rotation the centrifugal force does not act in a direction to throw gritty substances out of the seal. In addition, with this arrangement the closed impeller cannot easily be replaced with an open impeller when stringy substances are to be pumped.

It is an object of the invention to provide a centrifugal pump which is capable of pumping gritty slurries and which avoids the need for frequent replacement of the wear plate.Water Pump Control Valves

It is a further object of the invention to provide a centrifugal pump which is capable of pumping gritty slurries but which can be modified to pump stringy liquids merely by replacing the impeller.

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2012-01-04

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