What is the best valve for an actuator
What is the best valve for an actuator
(OP)
Hey all,
Operations has had problems with the current actuated startup bypass valves. The fluid in this aplication is Blend Oil. There is currently a 30s shutoff actuator on a 1/4 turn ball valve. Because only about 1/8 of the turn is actually doing something, they find it shuts off the flow too quickly.
When I asked a vendor about a V-ball valve he said it wouldnt help the application. Is he right or wrong?
Typically what are the best valves to use with an actuator? Is this too much of a broad question?
Thanks
Operations has had problems with the current actuated startup bypass valves. The fluid in this aplication is Blend Oil. There is currently a 30s shutoff actuator on a 1/4 turn ball valve. Because only about 1/8 of the turn is actually doing something, they find it shuts off the flow too quickly.
When I asked a vendor about a V-ball valve he said it wouldnt help the application. Is he right or wrong?
Typically what are the best valves to use with an actuator? Is this too much of a broad question?
Thanks





RE: What is the best valve for an actuator
It is possible that a V port ball will work, however depending on the severity of your problem, you may need a globe-type control valve that can be accurately adjusted through most all percent of accuator travel. There are several common flow to travel curves for various valve types and port styles that may allow you to nicely proportion the % open and % flow to solve your particular problem. You just have to get the valve Cv-%travel characteristics off the vendor's websites, calculate the flow at your particular start-up and shut-down pressure increases and decreases and find a good match.
I don't particulary like control valves in recycle lines, but sometimes there's just no other way.
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RE: What is the best valve for an actuator
Geoffrey D Stone FIMechE C.Eng;FIEust CP Eng
www.waterhammer.bigblog.com.au
RE: What is the best valve for an actuator
If it's a pneumatic actuator, stroke speed controls are available as NAMUR pad mount, with long-taper needle valves, with a check-valve bypass. THese are offered for independent control of clockwise and/or CCW times.
I can't see why a v-ball wouldn't also help, and something like the Worcester CPT with custom-selectable V-angles will let you really dial it in.
The v-ball or V-port is used if the primary function of the valve is modulating. The cycle length control is for closing speed of an on-off (isolation) valve.
RE: What is the best valve for an actuator
Keep in mind that no proper throttle valve will give you a reliable shut-off seal. For a bypass I'd back up a V-ball with a ball valve that is normally shut during steady-state operations.
David Simpson, PE
MuleShoe Engineering
www.muleshoe-eng.com
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RE: What is the best valve for an actuator
I would try the v-ball first, and see if it takes care of the problem.
There are many "v-ball" designs, not all of them necessarily "v" shaped. I call these characterised ball valves, and they come in all types.
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RE: What is the best valve for an actuator
It is a 2" valve. The vendor says he could supply a 60s actuator but it would be 5-6 weeks for delivery and I don't think I can wait that long as this project is already a bit behind schedule.
I spoke with my supervisor and he also thinks the V-ball should work. We used a program to show Cv vs. %open and with a V-ball it has a much large Cv when the valve is almost closed. I believe we will give the vendor a call and ask why he thinks it won't work.
Thanks again for the input.
RE: What is the best valve for an actuator
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RE: What is the best valve for an actuator
RE: What is the best valve for an actuator
Going the Big Inch!![[worm] worm](https://www.tipmaster.com/images/worm.gif)
http://virtualpipeline.spaces.msn.com
RE: What is the best valve for an actuator
We're getting the cart before the horse making specific recommendations without looking at specific process numbers.
A ball valve has a equal-percentage flow characteristic. If there is only meaningful restriction in the bottom few percent of travel, it's because the flowrate is low or otherwise the required Cv for that operational mode is low. Even tho' the chararacteristic is =%, the Cv is HUGE, and it is entirely possible that the INSTALLED characteristic is unacceptable. Once you're flowing all the system can provide, it matters not how much more capacity is available in the valve.
A V-port valve puts more restriction at the low end. The Worcester valve I mentioned has a v-shaped control seat and angles as small as 15 degrees are offered. That provides a signicant restriction in capacity and in this case would move the point at which meaningful restriction begins to occur up away from the low end. the V-shaped seats still have =% (well actually parabolic, but very similar) characteristic, but the entire curve is MUCH lower, matching the valve capacity to the requirements of the system.
The original question was
"There is currently a 30s shutoff actuator on a 1/4 turn ball valve. Because only about 1/8 of the turn is actually doing something, they find it shuts off the flow too quickly."
I read that to mean that meaningful restriction starts (30/8) 3.75 seconds from closure, so slowing down the actuator resolves this complaint. Will the pressure drop suck the seats out of the valve? Don't know-no process conditions are stated. Don't know what kind of valve he has, Pneu or electric actuator, Process fluid, pressure, DP, Temp, flowrate, pipe size, or any of that good engineer stuff that is necessary to make good application decisions.
A globe valve with a control plug would make a good throttling bypass, but the same criteria need to be supplied so the Cv can be calculated and the proper trim selected. Metal-to-metal seated globe valves USUALLY have class IV sutoff (FCI 70.2) so you have to decide if you are willing to put up with the dribble when it's closed. Also the title of the thread was "What is the best valve choice for an actuator" and if he was serious about keeping the actuator, then the globe valve would not be compatible. Note that actuators are customarily chosen to meet the demands of the valve, not the way it was stated above.
There is a best valve choice for every application. But you have to know the application.
RE: What is the best valve for an actuator
In many Eng-Tips forum responses, there is a tendency "to do the complete design" on rampant second guessing, which usually does more damage than good. (I'm guilty, but have started trying to limit to bare minimums, except maybe right now.) I think its only natural for an engineer to try to do a complete design, but the basic facts are that anything appearing to be more than a simple exchange of opinion, a suggested method of solution or a complete WAG ... IS NOT and we should all just try to answer the questions as written. (Note! By this, I'm not suggesting your post (or any herein) is/are inappropriate in any manner). So all should remember this is certainly not the proper place to do or expect to receive a proper engineering design or recommendation and posting anything implying or perporting to do so is totally unethical. (same note) Anyone receiving a "tip" here must realize that responsibility for implementation of any such "tip" remains with him/her alone and they should be qualified to evaluate, and should evaluate in every detail, any information received.
So, considering the above, I can't help but feel that while needing to know "the rest of the story" would allow all of us to do a proper engineering design or make a qualified recommendation of some kind and take responsibility for our design and recommendations, its just not going to happen on an internet forum, nor should it be expected. I think the OP realizes this by his original questions. All he asked were, "Is he right or wrong?" and, "What is the best valve to use with an actuator?" He obviously isn't expecting anything more than a bit of opinion, even though, he received quite a bit more. So, all in all, IMO the OP received the level of response appropriate to the level of the information given, the level of the response apparently requested, and the answers to his questions, without "us" knowing any of "the rest of the story". So, without additional information, I'll stick to my globe valve, as they typically offer the best overall flow control possiblities. And IMO, he's not serious about keeping the actuator, since he says, the vendor could supply a 60s actuator but it would be 5-6 weeks for delivery and I don't think I can wait that long". So, changing actuators shouldn't be an issue, but if it is, I'm sure he'll consider it.
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RE: What is the best valve for an actuator
I have previously designed a valve system for projects where fine control was in one direction and the balance went to bypass. I found the trick was to fine control the main outlet flow by adjusting the bypass flow or pressure. This was for applications where the inlet flow was constant (in fact the majority of applications were gas turbine exhausts but it has also been applied to liquid flow situations)
Ball valves and gates are normally used for on off flow, not for control and they usually experience high wear rates if held partially open. If you must use a ball, perhaps a special hydraulic stepping acuator can be used. Typically these have about 150 steps for 90 degrees opening and stay fixed at any position if a pulse signal is not received. They are very expensive though, and may not be supplied without a control valve. There used to be some pneumatic stepping actuators from Sweden but I would have to look in my archives to get the manufacturer.
I think however you will need to look at your system, see what flow options you desire and reselect your valve/actuator to suit. If there are a large number of valves there may be options to combine flows or use one actuator control for more than one valve to economise.
RE: What is the best valve for an actuator
If you have a pneumatic actuator, there is a good chance you can stick with your current set-up and add this control feature to resolve your problem.
BCD
RE: What is the best valve for an actuator
You might need a control valve, but a globe valve could have a smaller Cv than a ball, and also a higher DP.
Have you considered an eccentric plug valve with a pneumatic actuator, similar to the "The Ranger QCT" (www.cahsco.com).
Maybe this type of valve could be suitable for your application.
RE: What is the best valve for an actuator
nick
http://www.deepwater-valves.com
RE: What is the best valve for an actuator