Minimum submergence in Vertical pumps

[mechatronic]

Hi all,

Is it possible to advise me how to arrive at vertical pump overall length?

Sorry I am not strong in the subject

What I have not understood is -

Min submergence = NPSH required - absolute pressure + Vapor pressure

If vendor gives NPSH required value can we find out Min submergence value ? if so how ?

or if Min sumbergence value to be given by vendor , how to arrive at overall length of the pump.

Kindly help with information

 

[BigInch]

"If vendor gives NPSH required value can we find out Min submergence value ? if so how ?"

Convert the two pressures to head (I assume you know both the absolute pressure and the vapor pressure of the fluid at your operating temperature) and calculate the submergence depth using the formula you already have.

The get the overall length you will need, you must know what the distance from the pump's mounting plate (or other similar reference point) to the minimum water level you will ever have in your sump or well when the pump is in the installed position, to which you must add the minimum submerged depth.

Be sure the minimum submerged depth is sufficient to prevent votex generation and pulling in air from the surface and that the overall length is not too close to the bottom of your sump or well.

http://virtualpipeline.spaces.msn.com

 

[pleckner]

The advise given is correct but if you are indeed weak in the subject, contact a vendor of vertical submerged pumps, such as Goulds. Tell them your appllication and they will suggest a proper pump with the proper shaft length; even if you don't buy it from them. The vendors are more than willing to help for free. You become a contact for future work.

 

[Artisi]

Submergence is a seperate consideration to NPSHr and not a function of it.

Quoting from Cameron's Hydraulic Data.

" Submergence must not be confused with NPSH regardless of whether the suction is negative (lift) or positive (flooded). Usually submergence is a term used to relate liquid level to the setting of a vertical immersed wet pit type pump with a free air surface at the liquid supply level." ... "The amount of submergence will depend to some extent on the design of the suction intake; i.e. a bell or a cone shaped entrance should require less than a straight pipe."

All other advice is valid for your needs, i.e.

From BigInch

"The get the overall length you will need, you must know what the distance from the pump's mounting plate (or other similar reference point) to the minimum water level you will ever have in your sump or well when the pump is in the installed position, to which you must add the minimum submerged depth.

Be sure the minimum submerged depth is sufficient to prevent votex generation and pulling in air from the surface and that the overall length is not too close to the bottom of your sump or well."

and from pleckner - contact a pump manufacturer or their agent if you are unsure of how to decide on the right submergence.

I must add that the inlet position in relation to the sump or well wall is also a major consideration.

What type of pump / installation and flow rate you are talking about.
Cameron's also gives submergence recommendation based on the flow rate.

Naresuan University
Phitsanulok
Thailand

 

[mechatronic]

Thanks to all who have answered - Refering to vendor is always there - but before asking any vendor I wanted to have a broader view.

BigInch , Thanks a lot for the practical tip.

mechatronic