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 = + h_p(s) + h_v(s) - h_vp    Fluid source at pump inlet

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

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

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

  NPSHA = + h_atm + h_z(s) - h_f(s) - h_vp     Fluid source above pump

  + h_atm = atmospheric pressure unless the source is pressurized  

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

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

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

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

NPSHA = + h_atm - h_z(s) - h_f(s) - h_vp   Fluid source below pump

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

fluid is at atmospheric pressure + h_atm

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