cavitation

You wrote:
"I can't understand how cavitation is formed in con. reducer and avoided in ecc. reducer"

First of all I think the person who told you this or wrote it did not make the point correctly or you missunderstood what was being said.

Concentric or Eccentric Reducers do not "cause" cavation. Cavation occurs naturally in all pump suction lines. The suction of a pump is the lowering of the pressure in the suction line to the pump. The lowering of the pressure of the line fluid lowers the vapor pressure in the line. The lowering of the vapor pressure allows the fluid to "Boil" at a lower temperature. When a fluid boils it starts to form bubbles. As the bubbles form they will join and become larger. These large bubbles create "cavities" in the suction fluid. When these cavities come in contact with the pump impeller they cause cavitation erossion.

You cannot prevent the formation of these tiny cavation bubbles. What you can do is reduce the potential for the build-up of larger bubbles and therefore reduce the impact of cavation erossion.

A reducer installed in the line does not cause or prevent the formation of the tiny bubbles or cavation. What it can do, if improperly installed is to provide a place where the tiny bubbles can collect, build bigger bubbles and then be sucked into the pump.

An Eccentric Reducer properly installed, with the Flat-On-Top (FOT) in a pump suction line does not provide a place where these bubbles can collect. They are swept right through the pump while they are small and insignificant. On the otherhand a Concentric Reducer or an Eccentric Reducer installed improperly (Flat-On-Bottom) in a pump suction line will provide a place for the tiny bubbles to collect and build. Then you have a higher effect of cavation erossion.

I hope this has helped.
Jop

That is a good article but I stand by my previous statement.