1 reply to this topic

[Alex.U]

Hi ,

Equipment supplier of screw FO pump provided us info regarding pump gauge suction pressure (please don't mix it up with NPSH).

Do we have some formula to convert gauge suction pressure to NPSH in case if our tank is connected to atmosphere (1bar). Does it mean that we will get 1bar+(-0.4bar) = 0.6 bar and this can be equal to 5.2m of NPSH for example for fuel?

Because normally our suppliers saying NPSH (between 3 and 6m) and gauge pump suction pressure normally is approx. 0 or 0.1 bar...

What for do we need to know gauge suction pressure of pump if all calculations we did is relative only to NPSH what is important!.

For closed system sometimes gauge can show minus in suction side but this is because we can get backflow sometimes...but in our case we have open system...

 

Greetings,

Alex.

Edited by Alex.U, 13 March 2017 - 05:29 AM.

[sgkim]

Alex, hi, 

 

There would be no way to convert gauge suction pressure to NPSH.  Pump vendor has no information on the "gauge suction pressure" of your own situation.  The pump vendor requires NPSH as minimum for the trouble-free operation of its specific pump model.  

 

If you do not meet the minimum NPSH required for the pump the vendor will suggest a certain idea to sell the pump to you - just to raise the suction tank liquid level or to drop the pump suction nozzle elevation to provide sufficient NPSH available.  The minimum allowance of NPSH available for centrifugal pumps is usually around 1~3 m above the NPSH required by the pumps.

 

Pumps can not be operated at below the NPSH required because the fluid will vaporize in the suction line.  Pumps cannot pump the vapor, and partial vaporization of the fluid in the pump may damage impeller and casing due to the abrupt contration of vapor bubbles.      

If a pump requires a positive suction gauge pressure, you shall notice that the pump can not be operated under vacuum condition.    

 

~Stefano Kim