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Automated Butterfly Valves upstream and downstream torques

Automated Butterfly Valves upstream and downstream torques

Automated Butterfly Valves upstream and downstream torques

This is probably a dumb question but I am sizing a high performance butterfly valve to a scotch yoke actuator and am confused regarding the open and closed position. If the valve is fail closed should the spring close it on the upstream or downstream side?

RE: Automated Butterfly Valves upstream and downstream torques

I think it may be depended on the actuator orientation and the spring setup. Should verify it with vendor or provide the orientation as required by the design, if necessary.

RE: Automated Butterfly Valves upstream and downstream torques

Assume you look at the butterfly valve from the top view, the disc shall close in the clock vise direction from the fully open position.

RE: Automated Butterfly Valves upstream and downstream torques

If you are considering triple offset butterfly then there is a preferred flow direction and that is for the flow to assist in closing the valve. These valves are torque seated and therefore have prescribed limits for the amount of torque that the shaft should be subjected to to limit the seat loading in order to maximise the life of the seal ring. If you are looking to apply a safety factor nominated by an actuated valve specification, I would advise against; such factors are not really applicable in this instance. There is minimal friction to overcome in these valves (basically the stem friction only) the only considerations should be: torque to open; dynamic torque; torque to maintain closed position.
The other thing often overlooked is that butterfly valves should be installed (cryogenic service excepted) with the stem horizontal, which keeps the line debris out of the trunnion/stem bearing area. This may necessitate the actuator being independently supported.

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