Flow Turbulence Cavitation


If given the choice we would prefer to have liquid flowing through the piping at a constant velocity.

Corrosion or obstructions can change the velocity of the liquid, and any time you increase the velocity of a liquid you lower its pressure, inviting cavitation problems.

Good piping layouts reduce fluid velocity. The good layouts would include:

  • Ten diameters of pipe between the pump suction and the first elbow.
  • In multiple pump arrangements we would prefer to have the suction bells in separate bays so that one pump suction will not interfere with another. If this is not practical, a number of units can be installed in a single large sump provided that :
  • The pumps are located in a line perpendicular to the approaching flow.
  • There must be a minimum spacing of at least two suction diameters between pump center-lines.
  • When all pumps are running.
    • The upstream conditions should have a minimum straight run of ten pipe diameters to provide uniform flow to the suction bells.
    • Each pump capacity must be less than 15,000 gpm..
    • Back wall clearance distance to the centerline of the pump must be at least 0.75 of the suction diameter.
    • Bottom clearance should be approximately 0.30 of the suction diameter
    • The minimum submergence should be as follows:
      • 20,000 gpm 4 feet
      • 100,000 gpm 8 feet
      • 180,000 gpm 10 feet
      • 200,000 gpm 11 feet
      • 250,000 gpm 12 feet

The metric numbers are:

  • 4,500  1.2 meters
  • 22,500  2.5 meters
  • 40,000 3.0 meters
  • 45000 3.4 meters
  • 55,000  3.7 meters