7 centrifugal pump priming seven

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Pump PrimingPump Priming

Prof. Dr. Eng. Maher HigazyProf. Dr. Eng. Maher Higazy

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Pump PrimingPump PrimingPriming Centrifugal pumps usually are completely filled with the liquid to be pumped before starting. When so filled with liquid, the pump is said to be primed. Pumps have been developed to start with air in the casing and then be primed. This procedure is unusual with low-specific-speed pumps but is sometimes done with propeller pumps12. In many installations, the pump is at a lower elevation than the supply and remains primed at all times. This is customary for pumps of high specific speed and all pumps requiring a positivesuction head to avoid cavitation.

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Pumps operated with a suction lift may be primed in any of several ways. A relatively inexpensive method is to install a special type of check valve, called a foot valve, on the inlet end of the suction pipe and prime the pump by filling the system with liquid from any available source.

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Foot valves cause undesirable frictional loss and may leak enough to require priming before each starting of the pump. A better method is to close a valve in the discharge line and prime by evacuating air from the highest point of the pump casing.Many types of vacuum pumps are available for this service. A priming chamber is a tank that holds enough liquid to keep the pump submerged until pumping action can be initiated.Self-priming pumps usually incorporate some form of priming chamber in the pump casing.

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