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Unread 16-08-2012, 01:12
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Tristan Lall Tristan Lall is offline
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Re: Seeking SMC Pneumatics Advice

Quote:
Originally Posted by IndySam View Post
Cv will vary according to the pressure used and even temperature, it must be calculated for every given situation. It is a poor value to use for our purposes.
I like the idea behind using Cv, but I don't like the way the rules implement it (it's under-specified), and I don't like the way many valve manufacturers are vague about it (not specifying the test conditions, not specifying the ratings independently for different products in the same line, etc.).

The Cv ratings can be measured according to several standards, which are not necessarily equivalent. (A couple articles in Machine Design describe the controversy: see the accusation and the rebuttal.1)

1 This is actually the first time I'm seeing the rebuttal article, so I'm not going to reply with what I thought I was going to write about the merits of the different standards. This requires more research—but maybe someone else should take that project on, and report back the bottom line on the appropriateness of using different standards to find Cv.