MICROFICHE REFERENCE LIBFUUW - Cd3wd.com

NPSHR is the maximum dynamic suction lift which a pump can handle withoutallowing the head (or pressure) in the pump to drop below the vaporpressure of the pumped liquid. If the pressure anywhere in the pumpingsystem drops below this vapor pressure, cavitation will likely occur whichcan sharply decrease the performance of the pump (see Section 4.2.5.)and if severe enough can damage the pump and/or piping (Rouse, 1950).To insure that t?* ’ ? phenomenon does not occur, the New Positive SuctionHead Available (NPSHA) should be determined for any pumping systemplanned, and should always exceed the NPSHA. From Figure 2.2NPSHA = Patm - HssL (or + HssH) - PV - HF (2.10)where P atm= absolute atmospheric pressure, andpV= vapor pressure of pumped liquid.P atmmust be obtained for the local atmospheric conditions and altitude,while Pv is a function of the liquid’s volatility at a given temperature.2.2.3 Power (HP)-Any water lifting device adds energy to the water on which it acts,either by raising it to a higher elevation and/or increasing its pressure,in the case of a sprinkler system. The rate at which the device adds thisenergy or head to the water is calledthe water horsepower (WHP) and canbe found asWHP=Q l Hm l ywk,(2.11)