What is the best valve for an actuator

[302Hugo]

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

 

[BigInch]

The typical ball valve will get pretty much full flow at 5-10% open and no slow down in flowrate until they reach 90-95% closure. If you're getting as much trouble as you seem to be having, I would suggest you look into a different port shape. Different port shapes may allow a smoother flow control in your application. You must find a valve with a Cv coefficient vs percent travel curve that is not allowing so much flow at low % opens and has a slower and more evenly proportioned flow adjustment on shutoff.

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.


Going the Big Inch!

http://virtualpipeline.spaces.msn.com

 

[stanier]

Another solution is to have two valve. One big and one small. The big one is used to macro control and the small one operates very slowly to achieve micro control.

Geoffrey D Stone FIMechE C.Eng;FIEust CP Eng

http://www.waterhammer.bigblog.com.au

 

[JimCasey]

Yet another trick: Most any electrical actuator manufacturer offers a cycle time controller. Electronic wizardry lets you dial in the stroke time that suits your purposes.

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.

 

[zdas04]

It does sound like a linerarity problem, you are going from basically full-flow to shut in the last second or so of your 30 second travel. My first choice for a solution is the same as yours, I'd put in a valve with more linear valve-postition vs. flow-rate curve and my preference would be for a V-Ball. I'm not sure what your valve salesman was thinking of--he's out of stock on V-Balls, maybe?

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

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

The harder I work, the luckier I seem

 

[Ashereng]

I would have though a V-ball would help. A globe would also work, but may be more expensive - what size is your valve?

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.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[302Hugo]

Thanks everyone for your posts.

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.

 

[BigInch]

Its not the actuator speed that's important. The valve will still stop all flow in the last 3 seconds of travel unless you change the port shape.

Going the Big Inch!

http://virtualpipeline.spaces.msn.com

 

[JLSeagull]

I support the globe for a throttling bypass valve at 2 NPS.

 

[BigInch]

Excellent recommendation ...IMO.

Going the Big Inch!

http://virtualpipeline.spaces.msn.com

 

[JimCasey]

A couple of things:
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.

 

[BigInch]

JC, First, To be 100% clear, I'm not critisizing any of your very informative post, which I highly appreciate, but I would like to mention one small thing. Of course you are totally correct in principle and I'm sure everyone on this forum would strive to produce a proper engineering design for every question asked, if it were possible. I just don't think it is. As an engineering "tips" forum, 100% of the information needed to do a "real design" or make anything more than a best WAG, will seldom ever be available, nor necessary if the OP knows the purpose of the forum and is qualified to do his job, nor is it practical. Hence I don't see the need to necessarily wait for all the information, because you'll never get it, nor should you expect to. And besides, an endless series of questions about the process and system configuration doesn't really make for a timely or very interesting forum. Example: What do we really know here? Blend Oil, 30s shutoff, 2", 1/4 turn ball valve. Note that the valve size was not even given until the OP 2nd post. At that rate, getting the whole story for this, flowrates, max min pressure, product, temperatures, attached equipment characteristics, piping configuration, etc. will take the next 90 days and he's already worried because of a delivery time of 5 weeks.

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.

Going the Big Inch!

http://virtualpipeline.spaces.msn.com

 

[martintw]

It seems like you have a control problem and both the valv and the actuator are not quite right.

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.

 

[bcd]

One option you may want to review further is known as "batch control" or "dribble control". It is a control feature that is added to automated valves that slows the last few degrees of closure. It is common for suhc things as filling paint cans, where you want to fill the can as fast as you can, but need accurate control at the end to get consistent amount of paint in each can.

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

 

[OCANDOA]

The option of a timed stroke operation from an electric might be a good solution, but the electric actuator could be expensive.

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" (

http://www.cahsco.com).

Maybe this type of valve could be suitable for your application.

 

[subtek]

Seems to me that you are trying to control with what is essentially an on/off valve. A V ball is a possible solution. However without knowing all the parameters its impossible to be 100% confident in any advice. I would suggest giving all the info to the control valve manufacturers and let them advise. The valve manufacturers are the experts on valves.

nick

http://www.deepwater-valves.com

 

[leecoop]

Another question is what power source is available for the actuator? Better controllability while maintining speed is a challenge, but I have seen it done using a globe valve and linear actuator with both hydrualic and pneumatic sources to the actuator. Example: 8 seconds closing speed with very precise positioning using hydrualic power.