Reducing Time stroking for Air Operated Valve - Positioner, Booster

[ICRH]

Let me explain our situation. Possibly someone else went through a comparable situation and might be of help.

Some present safety related valves were just conventional control valves in origin. Because of a licensing change these valves needed to be qualified as safety related. Not only a nitrogen supply was implemented, but also the positioner, the converter and some other accessories were replaced by safety related (or dedicated) ones. The opening and closing functions happen always through the positioner. These are 2 inches rising stem valves from Masoneilan.

The problem came out now that some acceptance criteria changed. Time to open must be reduced in 10 seconds. With the high volume actuator and the present positioner installed (Fisher 3582) is impossible to get such a reduction.

If any other site had had the necessity to select a safety related (dedicated) and high capacity positioner we would appreciate any suggestion on models. If circumstances made it impossible we are also thinking about including a volume booster, and again any suggestion would be very welcome.


Thanks for your time.

 

[vpl]

Are these pneumatic or electric? What is the current opening time? Do the valves also have a safety-function to close?

Patricia Lougheed

******

Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.

 

[ICRH]

Patricia

Answering to your questions ...
- They are pneumatic.
- The opening time is 20 sec.
- The closing is not a safety-function but it is the desirable normal position.

It is relevant to know that the actuator volume is high.

tHANKS

 

[rcchap]

Does your valve need to be full open in 10 seconds, or does it need to be throttled to the required flow in 10 seconds? What system is this on and what is the required flow?

I don't know if it helps, but we had a Copes Vulcan control valve on the discharge of our Aux Feedwater pumps (3" line, approx 200 gpm flow). In this case, the valve was fail open, air to close, and we had safety related N2 supplied to ensure that it would throttle properly and prevent pump runout if we lost Instrument Air. It's a different situation than yours, but changing to a fail open valve might reduce the time because the spring will open the valve and you won't have to rely on the positioner to do that. I am fairly certain that these valves would open in less than 10 seconds (but they had a 1" stroke).

Another thing to look into would be to change the trim type, although this could be problematic for controlling flow. If your trim is a linear or equal percentage, you could get to your required flow more quickly by switching to a quick opening trim.

I know I didn't really answer your original question. As for a positioner, I would call Fisher and see if they have a model that meets your time requirements with a quicker response time and a smaller dead band.

 

[vpl]

FYI: The original poster also posted this question in the valve forum. See thread408-316671.

Patricia Lougheed

******

Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.