Minimum sumergible level - NPSH available

[PalomaP]

I understand that it should be a minimum sumergible level for vertical pumps to avoid vortix. However how to calculate the NPSH available of the system? Obviusly the static head has to be at least the minimum sumergible level? Any comments?
Thanks a lot

 

[BigInch]

The minimum liquid level in your sump must be above the pump intake by the vortex prevention depth. Minimum distances from pump intake to sump walls and to sump floor should also be maintained.

NPSHa should be calculated from that same minimum liquid level to the pump centerline.

http://virtualpipeline.spaces.msn.com

 

[GregLamberson]

NPSH is a function of the system, which is its sucton head or lift, frictionas, and the vapor presure of the liquide being handled. NPSH for a new system can be calculated, if it is anexisting installation can be determined by pressure/vaccuum gauge.

By definition, NPSH is the net positive suction head above the vapor pressure of the liquid at the suction flange of the pump top maintain a liquid state.

You can use NPSHa = Hp +/- Hs - Hf - Hvp

Basi8cally NPSH = static suction head (if any)+ atmospheric pressure (if open tank) or the psitive pressure (if closed pressurized tank) which is Hp above. Then subtract the vapor pressure (Hvp), friction losses (Hf) and static suction lift (Hs).

The NPSHa is directly dependent on the suction conditions and in turn defines the required suction characteristics of the pump. You haven't provided any detaiuls, but when you consider a typical application of NPSH as it affects the system, the keys are head-capacity and pump suction size.

Greg Lamberson, BS, MBA
Consultant - Upstream Energy
Website:

http://www.oil-gas-consulting.com

 

[PalomaP]

GregLamberson, My concern was about confusing minimum liquid level and NPSH available when working with vertical pumps...

 

[GregLamberson]

My apologies, BigInch as usual has nailed it.

Greg Lamberson, BS, MBA
Consultant - Upstream Energy
Website:

http://www.oil-gas-consulting.com

 

[BigInch]

Easy. Darcy asked me the same question in 1853.

http://virtualpipeline.spaces.msn.com

 

[quark]

huh... BigInch, you are taking advantage of my weak memory.

 

[BigInch]

I could never take advantage of you Quark. Actually

asked a number of NPSH questions just a couple of days
ago.

http://virtualpipeline.spaces.msn.com