Control Valve Actuation


Thread Starter

Alberto Lucas

I would like to know the meaning of the acronyn FLO "FAIL LOCKED AND EVENTUALLY OPENED", used for control valve actuation in a process control system.

Alberto Lucas

Suresh Kumar Devapiriyam


Fail lock means that you need an air lock relay in the control valve to hold the valve opening at its "last position" just before the air supply failure. However due to inherent leakage in the air lock relay, it can not hold the valve in this last position indefinitely. In that event, the valve should go to full open position from its "last position".

To achieve the above the control valve should be equipped with a AIR FAIL TO OPEN (i.e.AIR TO CLOSE) actuator with a AIR LOCK RELAY.

Hope it clarifies your query.

With warm regards
D.Suresh Kumar
IDEA Limited
Phone : +91-44-8225363
Fax : +91-44-8257134
email : [email protected]
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In addition to the other response, I would like to add that "zero" maintenance induced air leaks are crucial in this type of setup. For example, any place there is an air connection in the system, it must be checked for leaks. As well as the need for a tight air system, be sure the air is clean and dry.

It has been my experience that Fisher has one of the best Trip Valves for this application. The Fisher 377 Trip/Lockup valve can be set up to Fail in Place, Fail Open, or Fail Close.

Jim Tucker (Sr.AOV Diagnostics Engr.)
Crane Nuclear, Inc.
770-429-4741 Xt. 4741
[email protected]

Béla Lipták

If you add a pressure repeater with a make-up supply, the air lock relay will hold the air pressure indefinitely.

Béla Lipták