Enter the pump differential pressure at shut-off (psi) and the suction pressure (psi) into the Shut Off Pressure Calculator. The calculator will evaluate the shut-off discharge pressure (discharge pressure at zero flow).

Shut Off Pressure Calculator

Calculates the maximum discharge pressure a centrifugal pump can produce at zero flow.

From Pump Head
From ΔP

Shut Off Pressure Formula

Shut-off discharge pressure is the pressure at the pump discharge when the flow rate is zero. In pump terminology, this is the shut-off or dead-head condition. For this calculator, the shut-off discharge pressure is found by adding the suction pressure to the pump differential pressure at shut-off.

P_{SO} = P_{suc} + \Delta P_{SO}
Variable Meaning Typical Units
PSO Shut-off discharge pressure psi, kPa, bar, atm
Psuc Suction pressure at the pump inlet psi, kPa, bar, atm
ΔPSO Pump differential pressure at shut-off psi, kPa, bar, atm

This means the calculator is combining:

  • the pressure already present at the suction side, and
  • the pressure rise the pump can generate at zero flow.

Rearranged Forms

If you know any two values, you can solve for the third.

\Delta P_{SO} = P_{SO} - P_{suc}
P_{suc} = P_{SO} - \Delta P_{SO}

How to Use the Calculator

  1. Enter the pump differential pressure at shut-off.
  2. Enter the suction pressure.
  3. Make sure both values use the same pressure basis and compatible units.
  4. Calculate the result to find the shut-off discharge pressure.

If you are solving for suction pressure or differential pressure instead, enter the other two known values and let the calculator back-calculate the missing variable.

Example

If the suction pressure is 30 psi and the pump differential pressure at shut-off is 50 psi, then the shut-off discharge pressure is:

P_{SO} = 30 + 50 = 80 \text{ psi}

So the pump discharge pressure at zero flow would be 80 psi.

Why Shut-Off Pressure Matters

Knowing the shut-off pressure is useful for pump selection, system protection, and troubleshooting. It helps estimate the highest discharge pressure the pump may see when flow is blocked or a discharge valve is closed.

  • Pump curve interpretation: Shut-off occurs at the zero-flow end of the curve.
  • Equipment protection: It helps check whether piping, seals, gauges, and casings are exposed to acceptable pressure levels.
  • Relief and safety review: It is often compared against design limits and protection settings.
  • Startup diagnostics: A measured shut-off pressure that differs greatly from expectation may indicate wear, incorrect rotation, air entrainment, or instrumentation issues.

Important Notes

  • Use consistent units: Do not add psi to kPa or bar unless the values are converted first.
  • Use the same pressure reference: Do not mix gauge pressure with absolute pressure.
  • Add algebraically: If suction pressure is negative, include the sign in the calculation.
  • Use shut-off differential pressure: The differential value should come from the zero-flow condition, not from a normal operating point on the pump curve.

Negative Suction Pressure Case

If the pump suction is under vacuum relative to atmosphere, the suction pressure may be negative on a gauge basis. In that case, still use the same equation and keep the negative sign.

P_{SO} = -3 + 42 = 39 \text{ psi}

This is a common point of confusion. The shut-off discharge pressure is not always equal to the differential pressure alone; it depends on the suction pressure entering the pump.

Common Mistakes

  • Using operating differential pressure instead of shut-off differential pressure.
  • Ignoring a negative suction pressure value.
  • Mixing gauge and absolute readings.
  • Comparing a calculated result to field data taken at non-zero flow.

Frequently Asked Questions

Is shut-off pressure the same as normal discharge pressure?
No. Shut-off pressure is the discharge pressure at zero flow. Normal discharge pressure is measured while the pump is actually moving fluid through the system.

Where does the shut-off differential pressure come from?
It is typically taken from the pump curve at the zero-flow point or from manufacturer performance data.

Can I use any pressure unit?
Yes, as long as all entered pressures use compatible units and the same reference basis.

What does a high shut-off pressure indicate?
It indicates the pump can generate a large pressure rise at zero flow, which may be important when checking component pressure ratings and control settings.