What do you mean NPSH in pump ? learn in easy way....

                                            NPSH

                   NPSH mean Net Positive Suction Head                                              

• Now, What is NPSH?

         NPSH = the total suction head in feet of liquid less the vapor pressure at the pump center line of liquid being pumped.

        So Net Positive Suction Head,

        = Static head + Surface pressure head – Vapour pressure of product - friction loss 

• NPSH is describing as term 1.NPSH required & 2. NPSH Available

1. NPSH required establish the pump capability of working in a minimum of positive suction head.
2.  NPSH available establish in original working condition of the pump in a process with positive suction head.

  Ø  NPSH available should be more than that of NPSH required to eliminate the risk of cavitation which can damage the pump.

       

•      For reducing NPSH-A.........

•     Use the double suction pump

•     Use lower speed pump

•     Use pump with larger impeller eye-opening

•     if possible use inducer. inducer can cut NPSHR by almost 50%

•     VAPOR PRESSURE:-

   Here it is necessary to know about vapor pressure because this term is required to understand NPSH & Cavitation.

         

     Vapour pressure is about liquid boiling, we know that water boiled at 212°F or 100°C.but this is only true at atmospheric pressure. Every product will boil (make bubble) at some combination of pressure and temperature. So that if you know about the temperature of product you need to know its vapor pressure to prevent boiling and formation of a bubble.

     

   “Vapour pressure define as the ability of the liquid to evaporate. Vapour pressure will go up with the temperature. The absolute pressure that is exerted by a liquid substance when sealed in a container containing only that substance and its vapor at a given temperature”.

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