Enter the atmospheric pressure, friction, and elevation into the calculator to determine the net positive suction head available (NPSHA).

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## NPSHA Formula

The following formula is used to calculate a net positive suction head available:

NPSHA = Ha +/- Hs – Hf + Hv – Hvp

- Where NPSHA is the net positive suction head available (ft)
- Ha is the atmospheric pressure (ft) (Typically 33.9 ft at sea level)
- Hs is the head due to elevation (ft)
- Hf is the head loss due to friction (ft)
- Hv is the velocity head (ft)
- Hvp is the vapor pressure of the liquid (ft)

If the pump is below the body of water Hs is positive. If the pump is above the water, Hs is negative.

Assuming the velocity head and the vapor pressure of the liquid are negligible the formula can be reduced to:

NPSHA = Ha +/- Hs – Hf

## NPSHA Definition

**What is NPSHA? **

NPSHA stands for net positive suction head available and is a measure of the total equivalent pressure head (ft) that a pump has available at its inlet.

## Example Problem

How to calculate NPSHA?

**First, determine the head due to atmospheric pressure.**The pump in this example is at sea level, so the equivalent head of atmospheric pressure is 33.9 ft.

**Next, determine the distance from the body of water to the pump.**For this problem, the pump is located below the water at 5ft.

**Next, determine the losses due to friction.**The equivalent head lost due to friction in this example is 6ft.

**Finally, calculate the NPSHA.**Since the pump is below the water, Hs will be positive:

NPSHA = Ha + Hs – Hf

NPSHA = 33.9 + 5 – 6

NPSHA = 32.9 Ft.