NPSHa 2

[rww88]

I have found the concept of NPSHa quite interesting and have been thinking through the classical definition. Will someone tell me if it is possible or likely that a NPSHa analysis could result in a negative quantity for NPSHa? I could refer to this concept as NNSHa (Net Negative Suction head available). If if fact this can physically occur, would this new term more corretly be referred to as Net Negative Suction head unavailable or Net Postive Suction head unavailable.

 

[25362]

To packdad, I believe one should think about the function of the machine. Centrifugal pumps (being of a dynamic character) add velocity head to the fluid. A head that is then partly (because of pumps' inefficiency) converted into static head (pressure) by the diffusing volute.

Thus any velocity head in the entering fluid, generally relatively small, whether the fluid is pre-rotating or not, would, by logic, contribute to the pumps' work.

The differential head is, as its name indicates, the difference between the total heads (Bernoulli) at discharge and suction.

With displacement pumps the NPSHA is estimated quite differently in this respect.

I hope the above helps to clarify thoughts.