Npshavailable Calculator
Plan your water tank & vessels project with our free npshavailable calculator. Get precise measurements, material lists, and budgets.
Reviewed by Abdullah, Technical Content Specialist
Formula
NPSHa = hatm + hs - hf - hvp
NPSHa equals the atmospheric head (hatm) plus static suction head (hs, positive if above pump) minus friction losses in suction piping (hf) minus the vapor pressure head (hvp) of the liquid at operating temperature. All values are in feet of liquid. Atmospheric pressure is converted using hatm = Patm x 2.31 / SG.
Worked Examples
Example 1: Standard Water Pump at Sea Level
Problem:Calculate NPSHa for a water pump at sea level (14.7 psi) with water at 68F, 10 ft static head above pump, and 2 ft friction loss.
Solution:hatm = 14.7 x 2.31 / 1.0 = 33.96 ft\nhvp = 0.339 x 2.31 / 1.0 = 0.78 ft\nNPSHa = 33.96 + 10 - 2 - 0.78 = 41.18 ft
Result:NPSHa = 41.18 ft (well above typical NPSHr of 5-15 ft)
Example 2: Hot Water Pump Application
Problem:Calculate NPSHa for pumping water at 180F with 5 ft static head and 3 ft friction loss at sea level.
Solution:hatm = 14.7 x 2.31 = 33.96 ft\nhvp at 180F = 7.51 x 2.31 = 17.35 ft\nNPSHa = 33.96 + 5 - 3 - 17.35 = 18.61 ft
Result:NPSHa = 18.61 ft (adequate but reduced due to high temperature)
References
Reviewed by Abdullah, Technical Content Specialist · Editorial policy