Valves trims

[sencae]

Good morning every once.
Presently I am working on Cv calculation of Valves with different shape of valve trim, if I change shape of stem trims Cv valve also changing.
For example in Quick opening amount of fluid discharge between seat and trim are more compare to Equal opening, please refer Figure 02.
If this statement is true then 100 % open condition the Cv valve won’t be same for Quick, Linear and Equal condition.
For example (100% open condition)
Quick valve (Cv value) = 2809
Linear valve (Cv value) =2600
Equal valve (Cv value) = 1150
Pease conform me whether this Cv valves and graph (figure 03) are correct or not.

Thanks
Senthil Ramajayam

 

[LittleInch]

Where did the bottom graph come from?

Makes it look like the valve isn't actually 100% open when you say it is?

How is anyone supposed to know based on the minute amount of information you've supplied??

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

 

[sencae]

Just for explanation purpose I have created myself, if it’s wrong please correct me on this.

 

[LittleInch]

No one can correct it as we have no idea how it was created. IT should by rights follow the other graph figure 01.



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

 

[SPDL310]

I have a couple of guesses where you may be going wrong to reach the figures you are getting.

1.) You are making the assumption that all the valves are traveling the same distance. They are not. The characteristic curve is Cv vs %opening; not linear travel. All of the valves should be traveling far enough to fully develop the Cv of the orifice. Presumably the orifice is the same size for all of your examples.

2.) You are calculating your Cv values incorrectly. For the contoured seat/plug combos the restriction area will move with the plug you will need to determine this through CAD measurements to make sure you are reporting off of the smallest restricted area.

3.) Somewhat tied to number 2, but are you limiting your total outputted Cv value? There should be a Cv value for the seat trim, and Value for the body. You add those values in series, and your combined valve Cv from opening can never be greater than that.

Hopefully that helps.

 

[Nick_Gray_88]

This is quite straight forward..

If the valve is the same lift/travel then the Cv will differ depending on the characteristic curve, if it is a drilled cage, if it is a contoured plug the max. Cv will be the same.

Cv through the drilled plug needs a reduced area for linear and equal percent to create the characteristic curve, so when at full open this reduced area reduces the overall Cv.

With a contoured plug, so long as your open area at max. travel is the same your max. Cv should be the same.

This should have the caveat that no control valve should be 100% open ever.