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.

 

[steamdog]

Most safety related valves are open/closed and not modulating. If this is the case there would be no need for a positioner, but rather the use of a solenoid. This makes the valve actuate MUCH faster, no matter what positioner is used.
Disclosure - I work for the Fisher rep here in NJ...

 

[gerhardl]

All air actuators can in principle be slowed either by throtteling the air flow amount into the actuator or out of the actuator.

The catch is that the necessary air pressures delta P and total pressure on one side of the actuator and/or positioner and/or any solenoid valve must be sufficient high to give necessary operational force, without disturbing the function of any of theese components.

If this can be done here is then the question, depending on layout, component and component size, considering spring return actuator or not, the work coombination af all components together etc. etc.

A correct placed throttle valve (needle valve or other), perhaps combined with a checkvalve, could in case do the job.

Apart from this I wold strongly go for steamdog's suggestion to throw away the positioner and replace with a suitable solenoid valve solution if possible, combined with reduced boring and throtteling as adviced.

 

[ICRH]

Thanks, steamdog.

However these valves must perform also a modulating function. For that reason still a positioner is needed.
I see two options:
- find an adequate positioner
- modify the control loop to acomodate two different paths: one for on/off and other for control.

 

[gerhardl]

OK. I would go fo your option #2: a separate emergency air filling or air emtying system (dempending on emergency operation mode), and at the same time isolate the modulating system, all operated by one or more serieal connected solenoid valves, if necessary backed by checkvalves. (If necessary redundant solenoid valves.)

 

[steamdog]

We do this all the time with a positioner. You put a 3-way solenoid in the pneumatic tubing between the positioner and the actuator. You will need to add a switch in your process that will trip the solenoid (venting the actuator quickly that will close or open the valve). Talk to a local valve rep, even our competitor because this is a pretty common practice.

 

[Boynt]

It sounds like you have your answer, but I thought I would throw my 2 cents in anyway. An application like this could also be done with an electric actuator made for control valves (not an MOV). The technology is newer to valve control, but has been around for ages in motion control and turbine controls. A servo motor is used with a roller screw or ball screw. That gives you the speed and positioning capabilities for both modulation and safety open. Full stroke can be accomplished in milliseconds, or minutes if you prefer. The positioner can be programmed to whatever you need. A spring can be added to guarantee fail open if power is lost. (Disclosure - I work for Exlar - the roller screw guys) Unfortunately we don't have SIL ratings yet.

 

[Compositepro]

You could also simply place a quick-exhaust valve or a volume booster (as required) between the positioner and the actuator.

 

[vpl]

ICRH

You posted this in the nuclear forum as well, and clarified that this valve has a safety function to go open. So saying, if you are in the US and therefore under NRC regulations, you need to have the valve configured such that it does not require power or air to open. As others have mentioned, this generally involves use of a quick-acting solenoid. The solenoid should allow rapid venting of all the air holding the valve in a closed or modulated position. Therefore, it won't affect the size of your pneumatic actuator.

I unfortunately have not had time to go find the NRC standard review documents for air operated valves. However, I'd suggest going the NRC public web site (

http://www.NRC.gov)

and looking for 1) standard review plan, 2) regulatory guides, and 3) information notices or generic letters.

Patricia Lougheed

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[vpl]

FYI: The original poster also posted this question in the nucelear forum. See thread466-316672.

Patricia Lougheed

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