Self Priming Pumps – Working and its Use

The self priming pumps are a special form of centrifugal pump that eliminates the necessity for external priming devices. If a centrifugal pump is found on top of the suction vessel or sump , it should be primed before it is started, to get rid of air from the suction line and casing, and to fill the suction line and casing with liquid. This should be done before starting the pump, otherwise the pump won't pump, and the air can harm the pump bearings. The priming operation on a regular centrifugal pump that's operating with a suction lift is done by pulling a vacuum at the top of the pump casing, using a vacuum pump or the plant vacuum systems. A self priming pump eliminates the requirement for this external priming mechanism.

The operating self priming centrifugal pumps work like any other pump that's operating with a suction lift and that has been properly primed. When the pump shut down or stops working, the liquid drains out of the suction line and back to the sump. However, as a result of the special design of the over-sized self priming pump casing, a amount of liquid remains within the bottom of the casing. When the pump is started again, the pump goes through a priming cycle, which generally takes several minutes. Throughout the priming cycle, the liquid that had remained in the pump casing is pushed by the impeller out the discharge, along side some of the air that is in the casing. This creates a vacuum at the impeller inlet, which draws liquid up the suction line. The priming cycle continues till all of the air is pushed out of the discharge and the water has worked its way up the suction line to the impeller. Then, the pump is totally primed and begins pumping like every primed centrifugal pump.

Self priming pumps can be used anywhere where a pump is running with a suction lift. The pump is also costlier than a regular centrifugal pump, however it eliminates the external priming mechanisms, and eliminates any bearings or motors in the sump that other pump types would possibly need. Normally, suction lifts are restricted to approx. twenty feet with self priming pumps.

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Created on Dec 31st 1969 18:00. Viewed 0 times.

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