how to resolve cavitation problem 3

[smain06]

I suppose that I have cavitation problem in the miltistage horozontal pump i want to know how to eliminate this cavitation and how to improve the performance for this pump
thank you for your help.

 

[Artisi]

First up you need to establish why it is cavitating - thát's assuming it is cavitation, why do you think it is cavitating.

Is this a new installation or has it always been a problem in an existing installation.

The usual cause of cavitation is insufficient NPSHa which can be from a multitude of reasons.

You will need to supply a lot more detail to get to the cause of the problem.

 

[stanier]

refer to

http://www.mcnallyinstitute.com

for technical papers on this issue. Then ask a more informed question.

Cavitation and the Centrifugal Pump by Griist is a classic text worth investing in.

 

[bk19702]

I echo other's sentiment on this in that you should familiarize yourself with the issue and provide more detail to the specific situation and what is occurring.

'Supposing' you have a cavitation problem indicates you are not entirely sure of what cavitation is to be begin with.

 

[MortenA]

More or less the same as the other guys says:

1) Determine if you actually have cavitation (dont assume)
2) Calculate your NPSHa
3) Compare to your NPSHr
4) If this agrees with your theory about cavitation then look for high losses in the suction line, elevation changes and the like.

There are no magical tricks here and the bottom line may be that you have a poor design here.

Best regards

Morten

 

[SeanB]

Stand along side the pump and listen. There is no mistaking the sound of a cavitating pump. Sounds like you are pumping gravel.

 

[sms]

As has been said, increase NPSHa...

"Why don't you knock it off with them negative waves? Why don't you dig how beautiful it is out here? Why don't you say something righteous and hopeful for a change?" Oddball, "Kelly's Heros" 1970

Please see FAQ731-376 for tips on how to make the best use of the Eng-Tips Forums.

 

[bulkhandling]

Have a look of the level in the pumpbox. Likely the level is low, or very low. Try to throttle down a little the valve (ball or butterfly) at the discharge pipe. This will reduce the pumping rate and force the suction level higher. Reduced flow rate also means a reduced NPSHr.

If the level is close to the maximum and pump is still cavitating - you probably bought a wrong pump or there IS a gravel in the pump.

Good luck.

 

[jme1976]

Some pumps sound just sound like that anyway.

 

[lowedogg]

A busted check valve will often rattle. Be certain of where the sound is coming from. Severe cavitation is (as mentioned above) quite unmistakable. It can be like a mini-earthquake originating from the pump.

Inadequate NPSHa is the most common culprit. The NPSHr published by the manufacturer is when the pump is brand new. If the pump is older, it will actually have a higher NPSHr due to wear on the pump seals.

Are you dealing with an open or closed system? If your system is closed, then you have some sort of leak, or the air was not vented properly at start up. Is there an air separator and air vents installed? Are they working correctly?

If your system is open, then check out the NPSH situation. Is there some connectivity in the piping system that is short circuiting the NPSHa? This could be in the form of a cooling tower bypass line connected to a low point in the return piping to the pump suction (for example).

Many details must be known about the system as a whole in order to diagnose the problem...

 

[Newmanite]

Do you have a screen or some type of debris mesh on the intake of the pump? Can you modify it if there is or perhaps fit a larger bellow on it to increase the available medium around the intake?