NPSH = Hp + HZ – Hvp – Hf

                Hp = Absolute pressure at surface of liquid 
in ft
           Hz = Height in ft of liquid above or below 
centerline of pump.
         Hvp = Vapor pressure head of liquid in ft.
           Hf  = Friction loss head between surface of 
liquid & pump  
                     suction pipeline in ft.
       NPSH = Net Positive Suction Head in ft.
      NPSHa = NPSH available + of the system.
      NPSHr = NPSH required + by pump manufacturer.
      NPSHa > NPSHr 
     As good engineering practice provide NPSHa-NPSHr = 1.5 
m of liquid.