NPSHr and pump suction specific speed(S)/pump operating speed relation

[hswang2]

Dear expert

I have some questions below.
1. Suction specific speed of pump and pump operating speed is the same thing or different. It should be different, and what is the relationship between these two characters?
2. As we increase the pump operating speed, the Reynolds no will increase, and we must get higher head result.
3. NPSHr=V^2 / 2g, and pump inlet velocity (V) = Q/ A , but how to get this relationship S = N Q ^(0.5) / NPSHR (^0.75)? and how to interpret the physical meaning that high value of S correspond to a low NPSHr.

Thank you very much.

 

[ione]

NPSHr is not equal to the dynamic pressure (V^2/2g) it is a parameter provided by the pump's manufacturer.

Moreover don’t take specific speed for suction specific speed.

http://www.mcnallyinstitute.com/09-html/09-12.html

Suction specific speed is a concept strictly related to cavitation. This figure indicates the amount of NPSH required for a given values of flow.

Specific speed is an indicator of the pump performance.