Valve actuator bleeder

[urfi120]

In case of gas leakage from stem to actuator body, there is a danger of actuator body rupture.

Is there any code/ standard that deals this problem? i-e Where to and where not to provide bleeder on valve actuators?

[ashfaqanwer]

I had a discussion with one of my seniors and his opinion is as under:

Gas is understood as the process medium.

There seems to be a problem in the question itself in the sense that
1. As the Actuator body and the Valve Body are completely separated from each other, the linkage is a mechanical one with a gland sealing at the control valve body end. Process Medium is never in contact with Actuator body even in case of process medium leakage,
2. Stem leakage will be leakage to the atmosphere not to the actuator.
3. As per above explanation process medium leakage cannot cause a leakage in the actuator body.
4. An exception from 1& 2 is a self acting pressure control valve (PCV) where instead of Instrument Air the process medium itself acts as the actuating medium. 5. All PCVs are fully designed for the operating medium and conditions.

However for academic purposes the actuator body and materials of construction are designed for low pressure i.e Maximum Operating pressure of Instrument Air with a safety margin while the Control Valve body is designed for the Process Medium, its operating Pressure and temperature etc.

[urfi120]

Dear Ashfaq,

i have attached a safety beacon regarding this possibility of leakage to actuator, please read and comment further...

Regards,
Irfan Ali
Mech Maint Engr, FFC

[ashfaqanwer]

The earlier reply considered the case of the control valve with actuator operating on instrument air.
However, the case of gear operated valve or the control valve with actuator operating on process fluid, there is a chance that the actuator body can get pressurized and relief system should be in place.
Normally, at plant site the control valves actuators work on instrument air and there is no chance that actuator can get pressurized with process service. However, at off-sites / remote locations, instrument air is normally not available for control valve operation thus process service is used to serve the purpose and actuator can get pressurized. If this is the case, provision of relief system is mandatory.

[urfi120]

ok i agree that this relief system is mandatory.
But is there any Code/ Standard related to this relief system?