This term describes the movement of the shaft in a radial direction.

This deflection can cause a premature seal or bearing failure as well as cause rotating pump components to contact and damage stationary components.

There are multiple causes for this radial deflection:

  • Operating off the best efficiency point (BEP) causes the shaft to deflect in a radial direction. The deflection is normally 60° or 240° from the pump cutwater, measured in the direction of shaft rotation if you are using conventional Francis Vane impellers with a specific speed between 1500 and 4000.
  • Dynamic unbalance of the rotating assembly.
  • A bent shaft.
  • A non-concentric shaft sleeve.
  • A non-concentric mechanical seal attached to a sleeve or shaft.
  • Misalignment between the pump and its driver.
  • Pipe strain can cause the shaft to be non centered.
  • Thermal growth in a non-centerline design can displace the shaft from the pump center line .