Centrifugal Pump Troubleshooting

You have four opportunities to trouble shoot centrifugal pumps and each opportunity can offer you a clue as to what is wrong with the pump...

A Little Bit More About Cavitation

Cavitation means different things to different people. It has been described as:

• A reduction in pump capacity.
• A reduction in the head of the pump.
• The formation of bubbles in a low pressure area of the pump volute.
• A noise that can be heard when the pump is running.
• Damaged that can be seen on the pump impeller and volute.
• Just what then is this thing called cavitation? Actually it is all of the above. In another section of this series I described the several types of cavitation, so in this paper I want to talk about another side of cavitation and try to explain why the above happens.

Cavitation implies cavities or holes in the fluid we are pumping. These holes can also be described as bubbles, so cavitation is really about the formation of bubbles and their collapse. Bubbles form when ever liquid boils. Be careful not to associate boiling with hot to the touch. Liquid oxygen will boil and no one would ever call that hot.

Fluids boil when the temperature of the fluid gets too hot or the pressure on the fluid gets too low. At an ambient sea level pressure of 14.7 psia (one bar) water will boil at 212°F. (100°C) If you lower the pressure on the water it will boil at a much lower temperature and conversely if you raise the pressure the water will not boil until it gets to a higher temperature. There are charts available to give you the exact vapor pressure for any temperature of water. If you fall below this vapor pressure the water will boil...