Chris Landis
Valve/Vacuum Product Manager
Parker Hannifin Corp.
Richland, Mich.

In recent years, much discussion has centered on Cv ratings (also known as capacity coefficients or flow factors) and whether or not American, European, and Japanese pneumatic-valve manufacturers rate valves the same way. With ANSI/NFPA, ISO, and JIS organizations all specifying slightly different test methods and rating criteria, the confusion is understandable.

Leaving that ongoing discussion to the respective standards organizations, here’s a look at the practical aspects of designing the most efficient and economical system without under or oversizing components. First, we’ll calculate Cvsfor standard pneumatic cylinders and examine Cvvalues for standard ISO valves, including 18 and 26 mm and ISO Sizes 1, 2, and 3. We’ll also chart average rod speed relative to cylinder bore size to pinpoint ISO valves that best match flow demands.

The approach is based on standard Cv calculations:

Cv=
Q

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