Define the net positive suction head, Civil Engineering

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Define the Net Positive Suction Head

All values in the equations are in units of feet. 

Note: Only use values related to the suction side of the pump.  

NPSHR = Net Positive Suction Head Required.  Provided by the pump manufacturer. This is the value required to prevent cavitation.

NPSHA = Net Positive Suction Head Available. Determined by equations:

NPSHA = + hp(s) + hv(s) - hvp    Fluid source at pump inlet

      + hp(s) the pressure head at the pump inlet (p/γ)

      + hv(s) the velocity head at the pump inlet (v2/2g)

  hz(s) = 0, inlet is approximately at the centerline of the pump

  NPSHA = + hatm + hz(s) - hf(s) - hvp     Fluid source above pump

  + hatm = atmospheric pressure unless the source is pressurized  

+ hz(s) the fluid source is above the centerline of the pump

Note: + hz(s) denotes the situation is a Static Suction Head   

  - hf(s) = head lost due to friction in the suction piping only

- hvp = vapor pressure head  Note: The higher the fluid temperature, the higher the hvp and the lower the NPSHA.

NPSHA = + hatm - hz(s) - hf(s) - hvp   Fluid source below pump

- hz(s) the fluid source is below the centerline of the pump, and the

fluid is at atmospheric pressure + hatm

Note: - hz(s) denotes the situation is a Static Suction Lift


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