M.11NPSH Calculator

Enter the pump suction conditions to check the risk of cavitation.

Liquid

Open tank: atmospheric pressure (1.013 bar at sea level; ≈ 0.90 bar at 1000 m).

Positive if the liquid surface is above the pump centreline, negative for suction lift.

Can be calculated with the M.02 Pipe Pressure Drop tool.

Results

Available NPSH (NPSHa)
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Safety margin
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NPSHa / NPSHr
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Status
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Vapour pressure
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Density
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    This tool is for preliminary sizing. Final design must be verified with material tests, the relevant standards and equipment manufacturer data.

    Formulas

    Available NPSH
    NPSHa = (p_s − p_v) / (ρ·g) + H_s − h_f
    Water vapour pressure (Antoine)
    log₁₀ p_v[mmHg] = 8.07131 − 1730.63 / (233.426 + T)

    Cavitation

    If pressure at the suction eye drops below the liquid’s vapour pressure, vapour bubbles form and collapse on the impeller, causing erosion, vibration and loss of flow. The NPSHr given by the pump manufacturer is the value at which a 3% head drop occurs, so NPSHa must clearly exceed NPSHr. With hot liquids, vapour pressure rises quickly and the margin shrinks accordingly.

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