**Related Resources: calculators**

### Cavitation Centrifugal Pump Minimum Safe Suction Head Formulas and Calculator

If the suction pressure of a pump falls to a very low value, the fluid may boil at a low pressure region (e.g. at the vane inlet). A formula is given for the minimum suction head, which depends on the fluid density and vapor pressure at the operating temperature and also on the ‘specific speed’.

Symbols used:

ρ = fluid density,

ρ_{a} = atmospheric pressure,

g =
Acceleration due to gravity

ρ_{v} = vapor pressure of liquid at working

V_{s} = suction pipe velocity

h_{f} = friction head loss in suction pipe plus any other losses

H_{a} = pump head

σ_{c} = cavitation constant which depends on vane

Units should be kept consitant..

Minimum safe suction head formula and calculator:

H_{min} = ρ_{a} / ρg - ( σ_{c} H_{a} + V_{s}^{2} / 2g + h_{f} + ρ_{v} / ρg )

Range of σ_{c}:

Safe region σ_{c}>0.0005N_{s}^{1.37}, where N_{s} = specific speed.

Dangerous region σ_{c}< O.OOO22N_{s}^{1.33}

A ‘doubtful zone’ exists between the two values.

Alternative cavitation formula

** Net Positive Suction Head Available **

NPSH-A = (((Pe – Pv)/ρ) x 10.2) + Hz – Hf + (V² / 2g)

where:

Pe = Absolute pressure in pumped vessel (bar)

Pv = Vapour pressure of fluid (bar)

ρe = Density of fluid (kg/dm³)

Hz = Minimum fluid level above pump (m)

(negative term if below pump)

Hf = Friction losses in suction side pipework (m)

Ve = Fluid velocity in pump flange (m/s)

g = Acceleration due to gravity (9.81m/s²)

Reference:

Mechanical Engineering Data Book, Butterworth Heinemann, Carvill, James 2003

Related:

- Centrifugal Pump Cavitation Review
- Preventing Cavitation Centrifugal Pump
- Cavitation Review Centrifugal Pump
- Centrifugal Pump - Net Positive Suction Head

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