Why centrifugal pump started with discharge valve shut off?

It is a common practice to start large capacity centrifugal pump with the discharge valve closed. If the characteristic curve for a centrifugal pump are examined it will be seen that when the quantity of water discharged is zero the power required by the pump is zero or very small amount. by starting the pump with discharge valve closed the power demand made by the pump on the pump motor is kept to very minimum .after the pump has started and the momentary high motor current demand has stabilized, the discharge valve is opened.

2.How does a priming pump of centrifugal type emergence fire pump work?

3.centrifugal pump diagram?
4.how centrifugal pump work?

5.How centrifugal compressors handle air, where centriful pumps do not?

◆Centrifugal pumps and compressors operates on an equivalent principle of changing K.E. of the rotating impreller to pressure energy of the fluid it handles.The fluid particles ar thrown out from the tip of the impeller with huge kinetic energies, which is coverted to pressure energy by the special volute design of the casing. Both cent. pumps and compressors operates on same principle but have a different clearence levels, and imepeller dimensions.The perfomance of a centrifugal pump will be largely dependend upon the wear ring clearence. Wear ring clearence is the clearence between the impeller and the casing at the inlet side of the pump. If this clearence is high, the fluid inside the casing will be pumped back to the suction eye, reducing pump efficency. For a traditional pump handling liquids, this clearance is relatively higher.For a centrifugal compressor, the wear ring clearence will be extremely small. This will permit handling of fluids of terribly low densities i.e, air .A large impeller can create very high angular velocites at the impeller tips, which traslates into high pressure energy of the fluid handled. The Auxilliary blowers for main engines and T/C blowers are centrifugal with large imepller diamters because of this reason. Large rotational speeds also increases the rate of energy transfer to the fluid handled, which also results in handling of light fluids.


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