Flow Analysis for V-Port Ball

[Sid89]

Hello Everyone,

Is there any way we can analytically calculate rated Cv values for custom cut V-port and Slotted balls (e.g 5degree V-Port ball or 3/8" slotted ball). What formulae can be used to compute it? If someone has done it and share the information, it will be really helpful.

 

[RVAmeche]

Rated Cv values are by definition provided by the manufacturer, which will have determined them through empirical testing or their own internal calculations.

If you're working with a manufacturer, it'd be easiest to ask them for the information. If you're modifying existing valves, I'd recommend setting up a test rig to determine it if you need accurate data. There's probably equations somewhere online but they will likely come with various assumptions you may or may not meet.

 

[Sid89]

We are modifying existing valves with a customized cut on balls and we do not have flow test rig setup. I was looking for some analytical calculations to compute rated Cv values for those customized V-port and Slotted Balls. We can make some assumptions while doing analytical calculations.

 

[RVAmeche]

I'm not aware of any public equations that factor in physical parameters of the valve to determine Cv. Possibly CFD with a 3D model of your new internals?

Out of curiosity, why not just get a different valve or change the trim instead of re-creating the wheel?

 

[Sid89]

RVAmeche ... Thanks for the CFD suggestion.

We often custom cut the ball as per service requirements and hence the need to compute rated Cv.

 

[RVAmeche]

Are you a third party doing this for various customers or internal to your plant?

Assuming by service requirements you're talking about solids content, fluid viscosity, or something of that nature, I think it'd be easier to select an initial ball valve w/ the Cv required by the system and then modify/cut the ball as you need to. Unless you're adding restrictions to the ball these will only increase the Cv of the valve. Since ball valves aren't really used for throttle control I'm not really sure why the Cv changing slightly is a big deal.

 

[Sid89]

We do it internal to our plant. Our production department requires rated Cv values for custom cut balls to adjust/measure process outputs. Have you ever modeled it in CFD?

 

[LittleInch]

Well if you've got a load of these already then you can do some tests and measurements and work out a set of cv versus cut angles.

It sounds like you're trying to be a V cut valve supplier on the cheap?

I don't think you'll get anywhere without testing. V cut ball valves are a law unto themselves.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[The Obturator]

Is your post query related to your other ongoing post on the problem where a ball valve is shearing off the soft seats? I queried you on that one whether you were modifying a manufacturers design and received no reply. Seems to be the case here.

Per ISO-4126, only the term Safety Valve is used regardless of application or design.

 

[RVAmeche]

I have not, and I think you'd still need to physically test one of the valves to confirm your model.

Maybe instead of modifying ball valves (and experiencing the issues in your other post), it'd be better to control process flow with a different type of valve such as globe.

 

[Sid89]

The Obturator and RVAmeche,

Its a different case than the one being discussed in another post. The other one is a full port ball and here we are trying to compute rated Cv values for custom cut V-port balls.

Globe valves are costly and we usually are able to control process parameters using V-port balls.

 

[fel3]

Find a local university with a hydraulics lab and see if they can test the valves. About 15 years ago I did several rounds of hydraulic performance testing for a fire hydrant manufacturer so they could get their hydrants certified in different cities. My client contracted with my alma mater to do the testing (I don't remember what the cost was). The university had moved most of the hydraulics lab that I had used during my undergrad in the late 1970s out of the engineering building and into a new facility where they did commercial hydraulics testing.



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