Pipeline size VS control valve size 1 - Eng-Tips

Hey everyone! I have been in a debate with one of our reps, regarding control valve sizing.


If I have a 12" line, and a 6" or 8" triple offset valve can do the required flow control (ie it has the CV and it isn't at too far opening angle), should I quote that? Is there a rule of thumb?

I was always told ISA best practices was not to drop more than 2 pipeline sizes below the line for a control valve. So in my example, the smallest valve should be a 12"er. However, I've tried to check this and the only thing I could find was in a book "control valve primer" by Hans Baumann, saying never go below HALF the pipeline size.

By the way, the media is water at ambient temp.


anyone have an idea what the right answer or rule is here? There is no rule, other than choosing your control valve by Cv, not pipeline size. If the step is huge enough that it will create a turbulent mess at the valve inlet and outlet, do a reduction for 10 or 20 pipe diameters upstream and downstream. To minimize, look into a valve with reduced port or trim features.

Often, pipes are sized for future flows in my experience. I can count dozens of pipes in which the valve size was half or less to achieve proper authority and good control. We generally do the lengthened reducers when the size will be 2/3 or less on larger pipes, but not at all on 1-1/2" and smaller. The few feet of higher-velocity water makes a nice place to stick a flow meter too.

Try this book: Fisher Control Valve Handbook

Rather than a rule-of-thumb or a limit on valve vs pipe size, the methods and equations are in there to determine the effect of reducers and such on performance.



Best to you,

Goober Dave

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