Butterfly Control Valve

I'm afraid your post isn't very clear- are you looking to have a pneumatically operated butterfly valve fail (default) to either the open or closed position in the case of air loss??

If so, all you need is a single acting, spring return actuator that is sized appropriately to the valve and material parameters. This can be set up to the required default position.

If you already have a double acting actuator it can still be done, but it is more complex and less reliable than using the appropriate type.

Take it apart and check the mechanism....

http://www.adamantvalves.com/Sanitary-Butterfly-Valves-with-Butt-weld-Ends-Pneumatic-Operation.html

Does torture come standard with that rack?

...and pinion?

Clearly what we have here is a failure to communicate. He seems to want the valve to fail closed, but it does not, and that is resulting in a local increase in frown density.

He probably did not get the double-acting actuator, and probably not even the spring-return style actuator.

Instructions:

(1) go purchase a double-acting actuator to fit on the stem of your wafer valve to take the place of the present one. Needs spring loading for when air fails to force actuator to return to the position you want it to.

(2) install the new one, and program it to open under air, close under air, whatever, and spring open or closed however you need it to.

(3) take the old actuator and pitch it over the fence and let the neighbors worry about it, or take it apart and play with it, then throw it over the fence, one part at a time.

OK, it not quite clear on what you are looking for,... I believe you want a normally 'Open Valve' (N.O.).

there is not enough information here, what size valve, on larger valves you have a gear box to assist in opening.

On smaller valves, it would be spring to close, (Normally Closed or N.C.) or spring to open (Normally Open or N.O.) and air to actuate it.

If I understand your problem right,you have a fail open butterfly control valve which will not close even if you put nitrogen to actuator.I assume this is a spring return actuator

If you put the correct air or nitrogen pressure in the correct side of the actuator and the valve would not close ,it means

a)The actuator is not sized properly

b)You are not putting the air pressure for which the actuator was sized

OR

c)The valve has an obstruction.If not carefully designed the disc will hit the flange/pipe ID in some design

Hope this helps