28 replies to this topic

[Afshin445]

Thank you kkka for your useful information.

[kkala]

I have traced another practice of 1970s, reflecting what probably is generally accepted today as a minimum. It says that discharge line design pressure shall be pump shutoff differential pressure + maximum suction pressure. In case there is a vessel with PRV on the suction line, it clarifies that max suction pressure shall be PRV set pressure + maximum static pressure.
This is Shell formula (see Ankur2061 post) explained in words (without HPD).
Shutoff differential pressure can be estimated as 1.2 or 1.25 x differential pressure at design conditions.
We refer to electric driven process or feeding pumps.

Edited by kkala, 27 January 2010 - 03:03 PM.

[ASOKA]

Dear All,

In many design criteria and practice I found two below formula for estimation of Shut-off pressure of Motor Driven Centrifugal pumps in absence of any Perfoemance Curves:

Shut-off pressure = 1.25 x Diff. Pump Pressure + Design Pressure of Upstram Vessel + Static Press. (From HLL).

Shut-off pressure = 1.25 x Diff. Pump Pressure + Static Press. (From HLL).

I want to know which one of above formula is correct. In this regards, I want to know how those formula is developed.

I appriciate if someone advice me in this regards.

Regards,

Dear all

hi , i am Ashok
i have a doubt regarding this , pump will reaches it shut off pressure at no flow condition , but at the same time we cant expect the vessel to be at its design pressure. but as worst case we generally go with the equation Shut-off pressure = 1.25 x Diff. Pump Pressure + Design Pressure of Upstram Vessel + Static Press. (From HLL).


can anyone clarify this

i have a scenario, the suction tank (a water tank) is operating at atmospheric pressure. the pump(centrifugal type) and the tank are located at the same elevation (no static head available). now if we do the hydraulic and find the pressure at the suction nozzle it comes less than atmospheric pressure, ie vacuum. whether flow will happen?

Thanks
Ashok

[fallah]

Your case not to be worse than suction lift situation!.It is adequate having NPSHA=NPSHR+acceptable margin