Cavitation in Valves

No, there's no ready formula. You'll need to evaluate the vapor partial pressure for your fluid and see if there's risk of happening.

With 1 barg inlet, it's a little hard to have some cavitation in some place... Unles your valve design allows some localized pressure drop spots. Depends on valve geometry.

Dear Ramannu

To enable a more precise answer please inform type of fluid, vapor pressure (Pv), critical pressure (Pc), Specific Gravity, max/norm/min flow rates, pipe size & schedule and type of valve.

Type of valve will determine the valve cavitation index Kc. The coefficient Kc inform the percentage of maximum pressure drop (P1 - Pv) that is allowed through the valve to avoid cavitation damage.

The coefficient Kc is determined by the valve manufacturer and can be found on the Technical Bulletin.

I used Masoneilan´s ValvSpeq calculation software considering P1 = 1 bar, dP = 0.9 bar, T = 45 C, fluid = water, flow rate of 1000 kg/h and the calculated result indicated an incipient cavitation. It means that, with the above data, there is nothing to worry about.

Again, a more complete answer will depend on the above requested data.

Regards

David Rodrigues

Dear David,

Thanks a nice reply, Its a water service valve, Max flow:150 meter cube per hour and Nor Flow: 100 meter cube per hour. Inlet pressure at Max flow is 1.4 Barg and Nor P is 1 BarG.

Its a Butterfly valve 100mm size.

Sp Gr, Pv, Pc shall be known to you.

If Kc=0.85 , what does this value states. What is incipient cavitation??

Kindly reply.

This seems to be pretty informative on your issue.

http://www.samson.de/pdf_en/l351en.pdf

Dear Sonave,

This file is good and useful, it will take time to read it.

you can tell if the valves is cavitating by increase levels of sound & vibration and pressure/flow fluctuation

if you can remove the valve then look for surface pitting

typically we design systems where the minimum pressure is 2.5 psi above the fluids maximum true vapor pressure (some customers want more margin)

got to have margin in preventing cavitation as calculations, property variations, and published fudge factors will only get you an estimate

I,'m sure that there is an increased level of sound. I was unaware that a 4" valve would flow 1000gpm.

This is the crux of the problem. The high flow rate is likely causing a transition from laminar to turbulent flow conditions and therefor there can be damaging cavitation in some areas of the valve or flow stream.

Recording the sound of the flows with a simple microphone solidly connected to the valve should document the condition and may help them trouble shoot.

Stepping up the pipe diameter to allow a 6" valve may or may not solve the problem.

Transferring the flow sounds to your ear with a screw driver can help you localize the area in which the problem is occuring if the source of the cavitation in the system is in doubt.

Best wishes,

Mr. Gee

The cavitation happens when at the given temperature pressure (or lack of it) is less than the vapour pressure of the liquid. This being water, at 45 deg C you need a vacuum pressure of about 0.1 bar (www.kayelaby.npl.co.uk/chemistry/3_4/3_4_2.html ) and you are very near it since your pressure drop is that much (1-0.9) this may create cavitation at the nozzles where the drops are taking place though the absolute pressure is high. Why you are having such a high drop across valve ?

dear all

this is amezing information about cavitation. Let me know even where cavitation can affect in piping. Because in my experience all condensate piping are having problem of corrosion. Is it because of this cavitation we have to use condensate pump rather than normal centrifugal pump to pump condensate.

C ur Vendor sizing calculation

IF CAVIATION INDEX Is INnegative valve will not caviatate

REGARDS

jose

Hi, ramannu!

First of all, a great big WELCOME to CR4. I hope you have some success in here, and I hope also to see you back in lots of blogs, offering your opinion.

From what you have said in your posts, there is nothing to indicate that cavitation is or will become a problem in the valve.

If you are really concerned, take the valve off for routine inspection, and check for pitting. No pitting, no cavitation worth thinking about.

Mark

Dear Mr.Mark,

This is a new valve, i am in the process to procure it. can i ask the vendor to have preventive measure. If i want to have some preventive measure, what shall i inform to vendor.

Hi, ramannu!

Tell the vendor that you want to avoid cavitation in the valve.

They will know the limitations of their product.

They might even ask you for the type of fluid, the flow rate of the system and the size of the piping going through the valve, and any other information they think they need, in case they think any of that information can make a difference in the possibility of cavitation.

When you give them that information, they will send you back details about how to prevent cavitation.

It's very unusual to think that there may be cavitation in a butterfly valve, however, since its operation is reasonably passive.

Mark

Chck this article

http://instrumentation.co.za/article.aspx?pklArticleId=2819&pklCategoryId=75

it has quite detailed description of cavitation in valves and the methodology.

As far as the method for testing is concerned, the only method I know is to chack the vibration spectrum of the valve at the rated parameters - temperature, pressure and fluid and analyse the spectrum.