Subject: Troubleshooting the positive displacement rotary pump. 12-04

No liquid discharge.

The pump is putting out a low capacity.

The pump looses its prime after it has been running for a while.

The pump is using too much power

Excessive noise and vibration.

Excessive noise or a loss of capacity is frequently caused by cavitation. Here is how the NPSH required was determined initially:

With the pump initially operating with a 0 psig. inlet pressure and constant differential pressure, temperature, speed and viscosity; a valve in the inlet line is gradually closed until cavitation noise is clearly audible, there is a sudden drop off in capacity or there is a 5% overall reduction in output flow. Cavitation occurs with:

  • A loss of suction pressure.
  • An increase in fluid velocity.
  • An increase in inlet temperature.

Here are some common causes of cavitation problems:

You are experiencing rapid pump wear.

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