Key equations for Process Engineers Process Design Process Equipment

Net Positive Suction Head definition – NPSH for pumps

NPSH definition

Net Positive Suction Head or NPSH for pumps can be defined as the difference between liquid pressure at pump suction and liquid vapor pressure, expressed in terms of height of liquid column. Suction head is the term used to describe liquid pressure at pump suction in terms of height of liquid column. When vapour pressure is also expressed in terms of equivalent height of liquid column, and subtracted from the suction head, the difference is npsh available at the pump suction.

where, hL is the head loss between 0 and 1,
p0 is the pressure at the water surface,
pV is the vapour pressure (saturation pressure) for the fluid at the temperature T1 at 1,
Δz is the difference in height z1 − z0 (shown as H on the diagram) from the water surface to the location 1,
and ρ is the fluid density, assumed constant, and g is gravitational acceleration.

NPSH Calculation

Normally the NPSH required by the pump at its suction (NPSHr) is specified by the pump manufacturer. Hence when you design a pumping system, you would most likely need to calculate the NPSH available (NPSHa).

You can easily calculate the available NPSHa using the equations from above.

Here are some more tutorials, references and calculators to help with those calculations.



Sign up for free if you are not a member already.

Get Heat Exchanger Design Software

Advertise with us

Advertise directly with us. Get links to your website. Reach out to our reader base of engineering professionals.
Email -