Control Valve Actuator Fail Position

[From:来自网络] [Author:admin] [Date:11-10-17] [Hit:]

The choice is fail close, fail open, or lock in last position. The one who determine the valve fail position is process engineer in term of their process requirement.


The fail close valve on spring-diaphragm type actuator is set up with the inlet pneumatic signal put below the diaphragm. The fail open valve is set up with the inlet pneumatic signal put above the diaphragm. All this set up is on the direct acting control valve.


The fail close or fail open actuator in the piston/cylinder actuator is done by the spring inside it (on the piston/cylinder spring type). If the spring force in some case couldn’t stand to move the stem to its failure position, we could use a volume tank or air tank to provide a pressure to ensure the valve stem move to its failure position.  This configuration is of course valve manufacturer special design and could be different from one vendor to another vendor.


Lock in last position actuator is done with lock up valve (valve that prevent the air to exhaust from the actuator in case of failure even).





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