How Can We Change the Action of a Control Valve?

Take it to the Instrument Workshop and ask, "Please change the action of this control valve." The Workshop Supervisor might want an account number to book the operative's time to.

Short answer: in most cases you will need to purchase either a different actuator or a different valve body in order to change the action of your control valve, and this decision needs to be made on the basis of process safety. Some control valves have reversible actuators allowing the user to make this switch without purchasing new components, but most do not.

The action of a control valve depends on the action of the body and the action of the actuator. Here we see two examples -- one air-to-open (fail-closed) and the other air-to-close (fail-open) -- made by combining different actuator types with a common "direct-acting" valve body:

If we change the valve body to reverse-action, the relationship between actuator type and failure mode reverses:

In all cases, the decision to make a control valve air-to-open or air-to-close should be based on the safety requirements of the process and nothing else. Decide which is the safest failure mode for the control valve (i.e. would the process be in a safer state if the control valve were to fail open versus if it were to fail closed?), then choose the appropriate valve action based on that. After making that decision, choose the proper controller and transmitter actions to give the loop the negative feedback it needs to be stable.

It should be noted that you can reverse the control action of a valve by installing a positioner on it, then configuring the positioner for reverse action, but this does not change the valve's fail-safe mode.

For a more detailed answer, see the sections in this book entitled "Direct/reverse actions", "Available failure modes", and "Selecting the proper failure mode":

http://www.openbookproject.net/books/socratic/sinst/book/liii.pdf

Yep. Just like that ↑.

Has this proposed change been through a HazOp Study?

It would help if you gave us some idea of the type of control valve. Many hydraulic and pneumatic control valves have porting NO or NC. One way would be to change the circuit logic. To open it and close it when you want to.

Hi,

Can the action of valves can be changed? Yes

How? depends on the type of valve,please give more details..

thanks