API 609 - Difference between Category A and B

[MPinson]

Hi,

API 609 related to Butterfly Valves is divided in 2 categories : A & B.

One of the piping classes on my project is giving me the choice between both, for all diameters, and there is no note saying when to use one or the other.

I'm guessing it is a matter of fluid.

Can someone explain to me concretly what is the difference between these categories, and when to use one or the other?

Thx

Mathieu (Piping Engineer)

 

[bcd]

You would get more responses if this is posted in Valve Engineering.

However, category A valves are "concentric" type. Also known as rubber lined butterfly valves. These are popular in low pressure systems (Class 150 or less), relatively lower cycle life, rubber liners are also good for abrasive slurry services.

Category B valves are "offset" type, meaning the shaft is offset from the disc, so they can handle higher differential pressures. Most of the offset types cause the disc to rotate freely from the seat after a few degrees of rotation, which minimizes seat wear and increases valve cycle life. The offset type can have rubber, polymer (PTFE or other), metal &graphite, or even metal seats. Lots of variety which makes these suitable for a variety of temperatures and pressures.

Note that the above is a generalization for each category, and there are many exceptions in each. But Cat. A is concentric and Cat. B is offset.

Google the terms concentric and offset butterfly valves and you will get links to many manufacturer web sites that will have plenty of pictures and videos showing the difference.

 

[casa903]

Hi

As a general philosophy Cat A (concentric) are used in utility services like air and water and Cat B (eccentric. may be double or triple eccentric) are used in process lines. Cat A are economical than CatB