Sensing cavitation?

[nocam1334]

Is there any way to measure or sense cavitation in pumps?

 

[JRLAKE]

Yes. Calculate your NPSHa and compare it to your NPSHr.

Sometimes you can hear cavitation (sounds like rocks being pumped) and sometimes you can't.

Check for pitting on the tips of the impeller and within the pump's nozzle area.

I'm sure others can offer more advice.

 

[BigInch]

Ultrasonics will pick it up.

http://virtualpipeline.spaces.msn.com

"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain

 

[BigInch]

and high speed photography.
thread407-218061

http://virtualpipeline.spaces.msn.com

"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain

 

[JRLAKE]

BigInch has better toys than I do.

 

[pumpking]

Those snails make another entry into eng-tips... Marvelous use of Spanish Holidays - how we have all learnt from the effects of Spanish TV !!!!

To answer the post, it has been mentioned, check NPSH against curve etc and then if you are trying to avoid operating at these points, put some kind of protection device onto the motor based on flow rates etc - not sure of your reasoning or application, but there are many things to assist you...



Ash Fenn

http://www.cdrpumps.co.uk

 

[habenikt]

Vibration analysis can detect cavitation. The frequencies of cavitation are less than 1x shaft RPM

Habenikt

 

[btrueblood]

"The frequencies of cavitation are less than 1x shaft RPM "

!

No higher frequencies, say from bubble collapse? I think that is what BigInch was alluding to...

Does your statement hold for multi-bladed turbine pumps, regardless of number of blades? What about multi-cylinder piston pumps?

 

[agmotes]

btrueblood is right, cavitation shows up in the 0 to 1x range. And with water, cavitation always occurs slightly unless the NPSHa is ten times or more than the NPSHr. One must note that cavitation causes the most damage at 2x NPSHr, and slightly less, say 1.5x, will cause enough cavitation that the collapse of the bubbles are cushioned by the large amount of bubbles around it, thereby decreasing damage to the impellers. On the other hand, more than 2x causes a decrease in cavitation resulting in less damage. On another note you can always look at the pump curve vs. the system curve and try to get the pump running right in the best efficiency point, or where the 2 curves intersect. The closer you can get to the BEP, the less cavitation you'll get and your pump will run much more efficiently.

agmotes