Reversed Fluid Flow


A couple of operating conditions could cause a reversal of the fluid flow in the piping:

  • A leaking discharge check valve in a parallel pump application.
  • Fluid separation caused by a sudden power failure to a running pump.

If reversed flow is not checked, the flow will enter the discharge side of the pump, and the pump will run as a turbine at the runaway speed determined by the available static head minus any losses in the lines and fittings. This reversed speed could reach a value in excess of 150% of normal speed

The magnitude of the reverse speed increases with:

  • Increasing pump efficiency.
  • Increasing specific speed.

The affect of this high speed reverse rotation:

  • Possible damage to the driver because of overload.
  • Water hammer in the lines that could rupture the pump casing or the lines.
  • Mechanical seal damage caused by the water hammer.
  • You could also get face separation in some single spring designs where the direction of the spring winding provides torque to the rotating seal face. Many Flexibox brand seals are manufactured this way.


  • On February 16, 2018