Special valve for cavitation[/] 2

[aatara]

Hello, I hace two multiorifice in serie that produce cavitation in a water coolant system of a nuclear plant. The DP is aproximately 3 kg/cm2 (Outlet pressure is atmosferic).

Do you know special valve to change my passive design and that reduce or eliminate the cavitation?. This valve must be ASME III.

Thank you in advance

 

[davefitz]

There are many . Try CCI ( control components inc) in Rancho Santa Margarita , California; they sell a "drag" style valve.

 

[Scotsinst]

I would say with only 3kg inlet pressure, you won't have much cavitation damage. Not enough to warrant buying an anti-cavitation valve. Do you need a backpressure control valve? A Masoneilan Camflex or a Fisher V500 with stellite trim would work well for a fraction of the cost.

 

[jlapp]

I agree with Scotsinst. CCI is VERY expensive and misapplied to applications that don't warrant the expediture. Masoneilan has many lower cost solutions.

 

[1ton]

Yeap!! I agree with you guys. CCI is too expensive for this application, for a 3 bar drop you don't need a drag valve. You also need to check the temperature of the water. It must be close to boiling temp. for it to cavitate at atmospheric. That would be my first check or reaction.

If the Control valve selection is not done properly then you might have cavitation in the valve body, and that would help also...
ex-CCI guy

 

[chandrasekaran]

Conval sizing program gives d.p. across valve /d.p. at each stage of Restriction device downstream valve, in addition to noise & cavitation.
High performance rotary valve with integral diffuser pack (ABB introl / Fisher / Metso Automation / Masoneilan) may be an option.I suppose this is in a cooling water return line handling large volume.

 

[4carats]

One way to define severe service is to calculate the percent of pressure drop across the valve. If it is over 50%, it will be severe service. Assuming your delta P across your valve is 3 bar, or 45 psid, while valve outlet pressure is atmospheric. Then [P1 - P2]/P1 is almost
[60 - 15]/60 or 0.75, i.e. 75% (>50%). You need a serve service valve.
You need a valve with a K-factor (or lost coefficient) large enough to absorb the fluid energy at all flows. Once you specify the flows, the effective flow areas for each brand/model of control valves can be calculated if trim geomtry is not too geometries, along with its trim exit velocity and trim exit Kinetic Energy. In marine engineering, at water fluid velocity of 100 feet/sec., pitting starts to occur at the tips of the propellers. 100 feet/sec is equivalent to 70 psi for water. Therefore you need to consider a control valve that will not give you a trim exit fluid Kinetic Energy larger than 70 psi.

 

[Scotsinst]

I'm afraid I must disagree with 4 carats (my home water faucet is not a severe service valve).
Cavitation is only caused by reduction below the vapor pressure at the vena contracta and increase in pressure due to pressure recovery, downstream. Cavitation causes valve and piping damage, not pressure drop, or pressure drop ratio.
If you ask CCI (an excellent company) they will explain that water at 3 bar does not have enough energy potential in the cavitation to damage hardened valve trim, which is why a simple valve with hardened trim is normally used in these services. The cavitation is not eliminated, it simply doesn't do much damage. The pipe reducer at the valve outlet and large pipe diameter downstream reduces the cavitation jet impingement on the pipe wall (the characteristic "rocks in the line" noise).

 

[BHMech]

Alternative to CCI Drag is Copes-Vulcan Raven Trim. These are less expensive, I can recommend an ex-CCI guy who now works for Copes if you like. They also have other trim designs that would suit your application.

 

[4carats]

Copes Vulcan offered my Company a valve using Raven trim free of charge. Our Company did not accept the offer because Copes Vulcan could not answer our Company the following questions:
1. Why is there no Pressure Equalizing Ring to keep the plug centered?
2. Why Copes Vulcan cannot give our Company a sizing program of the Raven trim?
3. Why Copes Vulcan cannot answer our Company how to characterize the Raven trim so that one valve can take the duty (the flow vs lift) of two valves (i.e. the bypass valve and the main valve)?
4. Why Copes Vulcan cannot tell my Company whether increased channel density (more turns) can be made in the disks for a valve of fixed size? (since they can only offer valves of limited sizes).
5. Why Copes Vulcan cannot let our engineers talk to their design engineers of the Raven trim in order to solve an engineering problem?
................
......
Our Company has decided to remove Copes Vulcan from our Approved Manufacturer's List except buying parts for the existing Copes Vulcan values that use Hush trim.

 

[cemo]

hi you guys
I just can you tell that 3 kg dp is nothing .Eventhough the application might have cavitation problem.
As somebody says cavitatasion couse damages on the valve trim.
You can reduce the cavition effect by using cavitation preventing plug and also you can protect your valve by using hardened or stellited trim.
This is that simple.
I can suggest you to go to Flowserve .They have many cavitation trims with VALTEK valves for severe service.

 

[Fog1]

Your pressure drops are quite low so there’s no need to go to CCI besides which the drag trim will more than likely force the valve size up one because of the large outside diameter it requires.

I could run a calculation for sigma, I haven’t but my guess is that you could get away with the old cage trim design as long as the pressure drop ratio’s can be accommodated in the nest.

Try Valtek or Valve Solutions.


Fog Jones

 

[itchyudder]

Hey guys...

Doing a little more detective work, I discovered that the patents for the Raven trim has been rejected by the US Patent Office. Apparently the Raven design is a copy of the DRAG valves provided by CCI.

 

[jsummerfield]

The Camflex is not the correct Masoneilan valve. Consider the Lincoln Log. Better still, send your requirements to Cor Val in Houma Louisianna. If they do not have a model that fits your application, sometimes (once in my case) they can fabricate the valve from billit with better price and delivery than Fisher, Masoneilan, Valtek, CCI and the other usual suspects. Plan on a serious support.


John

 

[spud1]

itchyudder,
Can you confirm your source for this information?
The Patent on the CCI Drag Trim Elaped in 1994, and as such no patent infringement could have occured. The RAVEN trim has already been accepted by the US Patent Office due to a number of unique features that make it very different from the CCI Drag trim, So different in fact that CCI has applied to the US Patent office to get the Copes Patent Relaxed so they can use the design features within their own Drag trim. I believe this is now tied up in the US Courts.

 

[itchyudder]

Hey Spud1,

I called a CCI guy and this is what they sent back to me this morning.

If you look up reexamination document # 6161584 in the public domain of the US Patent & Trademark Office, you will see that as of May 2003 the Patent office has reviewed and rejected the previously accepted Copes patents. Copes has the til the end of this November to file against the Patent Office's decision. But Copes does have the right to trademark the "Raven" name. So they can tack that on to anything else they want.

That's all I know. He's also forwarded me a copy of that 6161584 paper.

 

[Scotsinst]

This is a very interesting string and I've learned a lot about Copes Raven trim etc.
I'm afraid the answer is still simple. A single step valve with hardened trim will work just fine.
Ask CCI, Masoneilan and Fisher how many drag trims, Lincoln logs or Cav III 2-stage trims have been applied with a 45 psig inlet pressure?
What is your water mains pressure? If your water tower is 100ft then you have about 40 psig. How many drag style trims are made by Moehn?

 

[jsummerfield]

Scotsinst was and is absolutely correct. Three bar/kg/cm2 is not severe service even in hot water - perhaps if extremely big and pretty hot. Separating the issues, the cavitation trim comments are more applicable at 103 kg or even 30 kg/cm2 at an elevated temperature.


John

 

[4carats]

People,

Please check the amount of energy released by cavitation.

The US Patent Office has rejected Copes Vulcan (Raven trim)to patent former CCI technology.

Itchtudder is correct. US Patent Office reexamination document 6161584 refers.

4carats

 

[aatara]

Thanks to everybody.

At the end, I decided to install 2 meters of Stainless Steel pipes after the last orifice to reduce the impact of the cavitation. Finally, I will test the wall thikness every year, with UT to study this problem in the future.