cavitation- a deep dive.

[mrsmackpaul]

So I think we are all sort of right and sort of wrong

Cavitation of pumps, which is what I was talking about is different than cavitation in a Cummins around the liners

That been said, I think we are all learning and that is what really matters 

Thanks for the thoughts Vlad

 

Paul

[Vladislav]

You are always welcome Paul. And sure the rest of the crue.

My collage research thesis had relation to centrifugal pumps. Not directly though. I studied mining and my diploma theme was "hydromechanization' - destroying of soft soils by stream of water and than transporting it away in a shape of pulp by big pipes. The pipes were really big, of 500-700mm ID and of 3-4 km of length. Pumps which were sopposed to move such volume of fluid were large correspondingly. And correspondingly expensive were cavitation issues.

The most troubles with the pumps were predicted by regimes they're operated at. The main subject was managing it and the most straight and correct way was setting right revs. But that was a problem at the time (early 90's) since powerful semiconductive devices were unavalible and the pumps spinned at the speeds typical asynchrone electric motors provided. That way speeds of flow in suction and supply pipe lines didn't corellate well bringing cavitation to pumps and settling derbits on bottoms of pipes clogging them.

[mrsmackpaul]

So I'm correct that cavitation in pumps is a result of the discharge been greater than the capacity of the supply to the pump

 

Paul

[Vladislav]

16 hours ago, mrsmackpaul said:

So I'm correct that cavitation in pumps is a result of the discharge been greater than the capacity of the supply to the pump

 

Paul

Actually you are Paul. As KT engeneer mentioned the effect takes place at a spot where pressure in the fluid drops lower than the evaporation (actually - boiling) point. Fluid boils at a certain tempertature but that temp depends on pressure conditions. On high mountains water boils at 90 or so Celsias not 100 for example. Same for every fluid. So if we have a certain avarage temp say 20C or 95C fluid doesn't boil. But imagine if the pressure drops locally, by sonic wave from combustion in a liner or by hard centrifugal force in a impeller. I mean some portion of fluid is forced moving and the sorrounding portion can't go same fast due to its mass or because of dynamic resistance in the suction channel. So that point evaporaits for short moment building a bubble, filled with the fluid wapor. In the next moment the bubble moves to another area where pressure is normal or that same area gets pressure change (sonic wave went further off) and the bubble gets pressed down very fast. It makes hydraulic hit like in a injection line and its now sonic wave hits surround. Attacking a liner or empeller wheel or whatever is on its way. Hundreds of thousands such hits applied to the same spot during prolonged time (hours or years) chip off the material making a cavit and than later a hole.

[mrsmackpaul]

I wonder what connection between  the ph level and cavitation in motors like Cummins and IH is

I'm thinking it might be as simple less corrosion and more strength mainained longer on components 

I do wonder if "cavitation" is a generic term coined for this type of phenomenon in some motors and is it actually cavitation  ?

 

Paul 

[Geoff Weeks]

Wiki has a pretty good definition.