what is positive suction pressure n negative suction pressure?

[jimkanajojo]

hi im yoga.currently doing a project about suction pressure effect on the performence of a centrifugal pump.i need informations about suction pressure of a centrifugal pump. for example, what is positive suction n negative suction, how to create it, the effect of these pressures on the performence of the pump n testing procedures. it would be kind enough if anyone can tell me where can i find these information on da net or mail me about it. i would appreciate more if anyone can explain to me in detail . thank you.

 

[dadfap]

jimkanajojo

NPSH is net positive suction head and there are two things to consider

NPSHA is net positive suction head AVAILABLE and that is provided by the system to the inlet of the pump.

NPSHR is net positive suction head REQUIRED at the inlet to the first stage of the pump to ensure that cavitation does not take place. The NPSHR is available from the manufacturer and can expressed as pressure or feet / metres of fluid over the pump intake.

As long as NPSHA is greater than NPSHA at maximum flow, your centrifugal will work.

DADFAP

 

[25362]

Dadfap has summarized the issue. However, I may add a few points only to better clarify the situation:

Although there is nothing wrong with pressure, the technical jargon prefers to use "lift" or "head" instead, and measure it in ft or m of liquid.

In previous threads you may find interesting discussions about NPSH_a and NPSH_r that may serve you as a good tutorial. Otherwise, any book on pump hydraulics may give you sufficient information. I'll mention only two that come to mind:

Karassik's Pump Handbook (McGraw-Hill)
Yedidiah's Centrifugal Pump User's Guidebook- Problems and Solutions (Chapman & Hall)

Good luck.