Determining Tubing Cv 1

[Timmigrant]

I'm designing a manifold and wanted to find out my flow rate through a valve, check valve and length of tube. I have the valve Cvs and appropriate formulae, does anyone have a good source for tubing Cvs of tubes in the following sizes: 1/4", 3/8", 1/2", 3/4" and 1"?

 

[Montemayor]

Although I have never heard of a "tubing" Cv, that doesn't mean that someone couldn't come up with one. However, based on the principles and reasons as to why the Cv principle was developed, I doubt you will find one.

Basically, the Cv principle is used to rate the maximum flow capacity through a device - a valve, for example. A tube doesn't qualify because you have stated it's principal flow determining characteristics: the I.D., the length, the configuration (is it looped? pig-tailed? straight?)

Until you identify the flow characteristic features, you can't determine an equivalent Cv. Can you be more specific as to where you obtain this tubing Cv criteria? Why would you want to apply it to tubing when you can resort to the conventional method of analyzing fluid flow through tubing: the Darcy-Weisbach relationship?


Art Montemayor
Spring, TX

 

[Timmigrant]

The reason I wanted to use Cv is that I wanted to develop an equivalent Cv for all the components on each of the branches entering the manifold. The branches all consist of a check valve, a solenoid valve and a length of tube. If I can find a Cv for the tube I can easily combine the Cvs of the valves and the tube into an equivalent Cv.

I have used some Swagelok data on determining the expected pressure drop over a length of pipe and correlated that back to an effective Cv, but the values I've calculated seem low, lower than my valve Cv of the same tube size. This doesn't make sense.

 

[MortenA]

Its not that difficult to claculate yourself (use a spreadsheet):

1) Set up the normal dP equations for a line for your lengths
2) solve to find flow rate for a dP of one psi

This equals Cv. Your methode does not make sense unless you know both ID and (equivalenth) length of your pipes.

Best regards

Morten

 

[Timmigrant]

Thanks Morten, that is essentially what I did was calculate an effective Cv, and used that in combination with my other valve Cvs. Thanks for your help guys.