FLOW TURBULENCE CAVITATION F022
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
- Vaporization cavitation.
- Air ingestion (acts like cavitation).
- Internal recirculation cavitation..
- Vane Passing Syndrome cavitation.