NPSH in pipeline boosting pumps 2

[Hierro]

How do I calculate the NPSHa in a pipeline boost application (no tanks as suction feed)? Say for instance, that pressure I expect in the suction point is 200 psig...

Thanks

 

[TD2K]

The NPSHA is the pressure at the pump suction above the fluid's vapor pressure.

So, take your suction pressure (in psiA) and subtract the vapor pressure of the material (in psiA). That will give you the pressure (in psi) above the fluid's vapor pressure.

Multiply by 2.31 and divide by the specific gravity just like if you were calculating the head for a pump. The 'head' will be in feet of fluid and is the NPSHA you have.

If the minimum suction pressure for the pump is less than the 200 psig (assuming this is the normal operating pressure), you should use the minimum suction pressure in the calculation along with the maximum vapor pressure. In all reality, you'll likely have lots and lots of NPSHA.

 

[hero123]

See the NPSH(A) calculation can be done by the following formula:

in case the storage tank is open to atmosphere:
NPSH(A) = P (atm)+ pressure due to height of liquid in storage tank - vapour pressure of the pumped liquid at working temeperature and pressure-pressure losses in the piping from storage tank to suction nozzle of the pump.

in case the storage tank is not open to atmosphere:
NPSH(A) = pressure due to height of liquid in storage tank - vapour pressure of the pumped liquid at working temeperature and pressure-pressure losses in the piping from storage tank to suction nozzle of the pump.

take care of the units and maintain a consistency.

p (atm) = atmospheric pressure
pressure due to height of liquid in storage tank = density x acceleration due to gravity x height
vapour pressure can be taken from charts or tables
pressure losses in piping can be calculated using several formulae available in handbooks.

hope this helps.