NPSH in submersible application

[aRom]

I would like to know if NPSH is a factor in submersible pumping applications?
We have a hydraulically driven centrifugal pump that has been converted to a submersible pump, the pump curve indicates the required NPSHr but this data is for a standard centrifugal application.
Am i right in thinking that only the minimum submergence calculation is applicable?
Cheers

 

[LittleInch]

No. The depth of submergence replaces the height difference between liquid level and level of the pump inlet. It will always be positive. Friction in the pipe is now zero. But pressure on top of the liquid remains as does the vapour pressure of the liquid.

But if your liquid is very volatile you can still have low NPSH.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Artisi]

The NPSHa will be atmospheric pressure plus submergence, simply check NPSHr against NPSHa. The only problem is ensure that submergence is sufficient to overcome air entrainment / vortex from the surface.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[bimr]

Minimum submergence is the amount of liquid required above the pump’s suction bell to prevent a vortex from being created. Vortexes endanger the pump because they can cause air entrapment and pre-rotation. You can estimate the depth using a vortex calculation.

 

[Artisi]

bimr:
if only it was that simple - vortices from side walls, bottom of the sump etc - no air entrainment but lots of pre-rotation and disturbed flow into the impeller eye - but that's another discussion

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)