How to Calculate a Net Positive Suction Head for a Pump in a Well

Measure the distance from the center of the pump suction to the ground. Pumps generate suction by moving a plunger in a sealed tube. You need to measure from the middle of the plunger. Add the result to the distance that the surface of the water is below the ground, which you should have been told when the well was drilled. The result is called the static head of the pump, the number of feet that the pump needs to apply pressure over to raise the water.

Subtract the static head from 33.957 if you live at sea level. Label this result as Result A. The 33.957 figure represents the atmospheric pressure at sea level, expressed in feet of water. If you live at a significantly higher altitude, then you you need to use the atmospheric pressure at your altitude. To express any altitude in feet of water, multiply the number of psi of pressure by 2.31.

Look up the loss of head due to friction for the length and diameter of pipe that your well uses. Subtract this number from Result A. Label this result Result B.

Subtract 0.62 from result B. The 0.62 figure represents the vapor pressure of water expressed in feet of water. This final result is the net positive suction head available for your well pump.