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"Pressure regulating valve" need help with what happens at no flow

"Pressure regulating valve" need help with what happens at no flow

"Pressure regulating valve" need help with what happens at no flow

(OP)
We have installed a pressure regulating valve from ARI in our thermal fluid system. The point was to reduce the pressure in a secondary heating loop to about 70 PSI to keep a relief valve from opening downstream that is set at 85PSI. There is a centrifugal pump after the ARI valve with a check valve after that prior to returning to the primary loop.

We tested the system today with both the primary loop pump and secondary loop pumps running. The Primary pump produced about 120 psi on the inlet of the ARI valve. A gage after the ARI valve read 60 PSI which was great.

Problem came after we shut off the secondary pump and left the primary pump running which still showed 120PSI at the inlet of the ARI. However after the ARI valve gage now shows 85-100 fluctuating alerting us that the relief valve was opening spewing oil out into our vent tank. Luckily we caught this before there was any mess but I am trying to understand what happened. I have attached a diagram of the pressure regulating valve

RE: "Pressure regulating valve" need help with what happens at no flow

Show us the P&ID of the system: Why do you think the 120 psig of the primary pump was not the cause of the relief lifting?

RE: "Pressure regulating valve" need help with what happens at no flow

My first "guess" is that the ARI is by no means a tight shutoff valve and that your fluid has leaked pass the ARI PRV. You then get the pressure swings you have described. The self-contained pressure regulators are also by no means quick response.

However, your description of the relative positions of pumps and the ARV PRV are not 100% clear to me.

If you could attach a system sketch that would be most helpful.

For example, what is at the "end of the line" for the secondary loop that maintains the 70 psig operating pressure?

RE: "Pressure regulating valve" need help with what happens at no flow

The pressure regulating valve only does anything at all when there is flow. If you stop flow in the secondary system, then the regulator will try to go fully shut, but they are not bubble tight and they all leak more than some (that helps with the linerarity on the low end), many of them leak a lot. Think of a tiny restriction orifice between the two systems--if you stop taking fluid from downstream, the upstream will continue to flow through the orifice until the pressures equalize. That is what is happening with your valve. There is no way to fix it without adding equipment since a decent throttle valve is a lousy block valve and a decent block valve is a horrible throttle valve. You need a high pressure slam valve between the two systems. This valve cannot be used for throttling and can either be shut on high press/manual open or shut on high/open on reset depending on your plant rules.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. —Galileo Galilei, Italian Physicist

RE: "Pressure regulating valve" need help with what happens at no flow

Errrr, Am I missing something here or is the valve diagram attached simply a spring relief valve? I assume flow is left to right. I can't see anything that controls the downstream pressure, only the upstream one. I suspect when running, this valve only restricted the flow resulting in lower pressure like an orifice plate. This valve is not a downstream pressure regulator.

If you get a proper tight shutoff control valve not this cheap relief valve then you might stand a chance, but the other posters are right, generally you can't rely on these valves to reliably seal on no flowt.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

RE: "Pressure regulating valve" need help with what happens at no flow

Well my goodness. That certainly looks like a self contained back pressure regulator (often used as a relief valve) and not a downstream pressure regulator.

But this point certainly doesn't explain the system's behavior (other than it has no chance of working as intended).

All the more need for a system sketch.

RE: "Pressure regulating valve" need help with what happens at no flow

(OP)
So the AE on the job specified this valve. We had some reservations. The OEM rep stated the valve would work so we went with it. Guess we should have questioned it more. I talked to someone at the OEM yesterday and he said similar to what you guys say that it is more of a back flow regulator

So it seems like we either have to install an automated shutoff valve prior to the valve or install a different unit. We have 3 of these so this is going to be a pain. I am guessing a new unit is the best option. Any more thoughts? Or advice on a brand/model recommendation?

RE: "Pressure regulating valve" need help with what happens at no flow

Your valve is indeed working as it is should, to hold more or less constant pressure at your primary pump discharge when it is running, and it will relieve when your secondary pump shuts down as it should.

So what do you want it to do?

RE: "Pressure regulating valve" need help with what happens at no flow

If you read it carefully what he wanted it to is to limit pressure in his secondary loop to less than 70 psi. A common inlet from the primary side then splits into a low pressure and high pressure loop. what he wanted is a pressure regulating valve to control the pressure downstream of the split.

Only a drawing will sort this out.....

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

RE: "Pressure regulating valve" need help with what happens at no flow

This might sound a bit critical of you but why if you " We had some reservations", did you install it. It really doesn't take much to look at it and realise that it is controlling upstream pressure, not downstream. To be fair to the OEM, he may just have misunderstood your requirement, but this is where drawings and schematics help...

You need a new unit. At running pressure you have just got lucky and the pressure drop across the valve you currently have when open and flowing is apparently enough to reduce your downstream pressure to the right amount. An orifice plate would have done the same thing.

You need a regulator controlling on downstream pressure. Google "pressure regulator" and ensure it controls on downstream pressure when you talk to the vendor. If you specify tight shutoff you might get that to start with or at least it might limit flow past the valve to an acceptable level or time to go and turn the loop off manually with an isolation valve. If you have clean fluid which is well filtered and the seals are good it might seal for quite a while, but there are very few people who would rely on a regulator to isolate flow.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

RE: "Pressure regulating valve" need help with what happens at no flow

(OP)
The reservations we had were for different reasons other than the workings of the valve but point taken that we should have reviewed the valve much more than we did. Here is a rough sketch of the piping and some pictures of the install just for the record

RE: "Pressure regulating valve" need help with what happens at no flow

Yep, pretty much what I thought.

Looking at this again though the valve MIGHT be acting as a constant DP valve if it takes account of the downstream pressure on the surface of the disc. The spring then adds up to about 60 psi so added to the 60psi you want d/s you want gives you 120. This depends on the upstream pressure being fairly constant and hence what you actually have is the upstream pressure minus a fixed amount as provided by the spring. It's not easy to tell if this is the case and nowhere near as good as a proper downstream regulator which will give you a fixed downstream pressure regardless of the upstream pressure.

If this is the case then either the valve is passing (quite likely) or your NRV on the pump is passing (also quite likely).

Your diagram is fine, but the control line from your pressure reducing valve is correct as far as this is what you want, but isn't correct as far as the valve you have which is a pressure relief valve, albeit probably being influenced by the downstream pressure.

I think you have a constant Differential pressure relief valve installed but with the difference between what you want (60-70 psi) and relief pressure (80 psig) there isn't a lot for the valve spring to play with and seat the disc.

does that make sense?

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

RE: "Pressure regulating valve" need help with what happens at no flow

(OP)
Yes it does. Thank you

RE: "Pressure regulating valve" need help with what happens at no flow

You have a minimum flow valve to insure minimum flow through the primary pump and to regulate its discharge pressure. The valve works as it is designed, and in fact installed in the flow-up position per manufacturer directions.

In such applications, the minimum flow should be routed back to the supply tank.

You can fix this by installing a tee where the valve is currently located and taking the branch to feed you min. flow valve back to storage.

The valve is working fine, but it needs to be piped correctly.

Good luck...

RE: "Pressure regulating valve" need help with what happens at no flow

I'm not understanding this conversation at all. The valve in the OP has a sensing port on the downstream side of the valve (assuming flow is up through the seat), so it is a pressure regulating (PR) configuration (NOT a relief valve, not a BP valve). These things are used all the time all over the world for pressure regulating. They don't need a particularly constant upstream pressure. They compare downstream pressure to the spring setting and changes in upstream pressure simply cause the valve to open or close more. They work well in flowing streams. The problem in the OP is that when the secondary pump was off, the PR valve did not seal bubble tight and stop pressure from rising in the secondary loop. No valve will both control pressure through throttling and provide a reliable positive seal, it is just too much to ask. This valve is fine.

The design looks workable. To prevent the PSV from lifting I'd put actuators on the first valve off the loop and the last valve off the loop (after the check, which is just as prone to leak in a no-flow situation as the PR) to slam on pump down (restriction orifices on the main loop and secondary loop might have allowed natural convection, with the pump off, but you didn't provide them so in a pump-down scenario you aren't going to get any flow to the heat exchanger loop at all).

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. —Galileo Galilei, Italian Physicist

RE: "Pressure regulating valve" need help with what happens at no flow

What?? Are you looking at the same post and photos I am? The valve in question is a pressure regulating valve, not a minimum flow valve. It is a sealed pressurised system.

Sorry but what you have written makes no sense at all (at least to me).

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

RE: "Pressure regulating valve" need help with what happens at no flow

Sorry Dave, the "what" was aimed at hacksaw.

Please correct me, but I can't see any sensing port either on the drawing or on the photos. What I can see is a spring acting via a spindle onto a disc. The thing making the disc overcome the spring force via the spindle is differential pressure across the disc no?

If the OP had gone a bit further down the fig 753, it would have been much clearer. See attached and go to page 3 where it says the application is a "spring loaded differential pressure control valve".

http://www.ari-armaturen.com/_appl/files_tb/files/...

I agree with you that it could work and apparently does when flowing and you have 120psi in the inlet, but needs better isolation, but the valve is still not what the OP asked for.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

RE: "Pressure regulating valve" need help with what happens at no flow

I admit that I tend to confuse, a bad habit of mine, but if you look at the data sheet and the operating manual for this series of valves you will note that there is a distinction between pressure regulating vs pressure reducing valves.

Yes, the valve in question does respond to differential pressure and the down-stream pressure must be taken into account when adjusting the pressure setting. So it says in the operating instructions. But note the following:
"Pressure regulating valves, spring loaded" are quite distinct distinct from
"Pessure reducing valves." One controls upstream pressure and used for minimum flow relief on pumps as the current installed valve does and the other controls the down stream pressure.

RE: "Pressure regulating valve" need help with what happens at no flow

I was going to color the original drawing to show the way the actuator worked, but I can't tell which of the things labeled "gasket" is actually a diaphragm. I looked at Masoneilan, Kimray, and Fisher and all of them have a reverse acting plug (this one is direct acting, the spring tries to shut the valve). The more I looked at this, the confuseder I got. I know the stem is free floating, and that there is an tiny hole drilled (look right above the leader line for "14"), but I'm having a hard time finding the control surface that gives me "decreasing pressure, open valve more". I'm sure it works, I just can't work out how in my mind.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. —Galileo Galilei, Italian Physicist

RE: "Pressure regulating valve" need help with what happens at no flow

(OP)
So the issue is either we did not have the spring set high enough to seat the valve, or the check or ARI valve was not sealing 100%

We can check the spring force tomorrow. I did not really get a chance to play with it much yesterday and maybe if I would have made the spring force higher it would have shut

Since our primary pump is always at 100% and the pressure really doesn't change much, I guess I don't see a problem with using the pressure reducing valves if we verify the ARI and Check valve shuts 100% - or maybe we install electric actuators on our gate valves before the ARI and after the pump

Definitely agree the pressure regulating valve would have been the correct choice. However, according to ARI their regulating valve can not handle the 400F temp of the thermal fluid so they are recommending a control valve which is even more money but we will get it one way or another.

RE: "Pressure regulating valve" need help with what happens at no flow

Throttle valves cannot be relied upon to seal, no matter how much spring force is on them. Sometimes (rarely in my experience) they do seal, but counting on it is unreasonably optimistic. The problem is that the act of throttling is really violent and you end up with wear patterns on seats and plugs. You sometimes get trash between the plug and the seat. There re just too many ways for them to go wrong. If the manufacturer's problem with the fluid temperature is the elastomer on the sealing surface, you can learn about alternative materials from the article I published just yesterday High Temperature Elastomers in Oil & Gas. The FFKM cross-links are pretty durable.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. —Galileo Galilei, Italian Physicist

RE: "Pressure regulating valve" need help with what happens at no flow

(OP)
Thank you. Good article

RE: "Pressure regulating valve" need help with what happens at no flow

I'm glad we all agree now... I agree with zdas04, this type of valve is much more commonly used for pressure relief or in constant flow, not as a tight shut off. More spring force will lower the pressure in the secondary loop and might assist a bit, but this and the NRV (any details of that?) are your weak points in terms of simple auto sealing on cessation of low into the secondary loop.

Of course the root cause is the pressure difference between your loops. DO you actually need to operate the primary loop at 120psi instead of 70?

If you do you might want to consider putting a single control valve on the secondary loop line down to 70 psi and a pump to get it back to 120 psi (where your two vertical arrows are in the sketch) and just getting rid of the three reducing valves? Just a thought.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

RE: "Pressure regulating valve" need help with what happens at no flow

I think that may be one of your problems. I've found that swing checks with vertical seats (as opposed to angled seats) don't seal with very low dP, and tend to not seal perfectly with a large dP. So when the secondary pump first shuts off (with about 40 psid) you will get a tiny leakage through the check valve. A couple of mL will obliterate the 40 psid and the PSV will lift. The process will repeat forever.

My guess is that you are leaking through the PR, the check, or (most likely) both.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. —Galileo Galilei, Italian Physicist

RE: "Pressure regulating valve" need help with what happens at no flow

Fair enough - another metal seated valve so high likelihood of it passing.

let us know how it goes with whatever changes you make.

good luck

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

RE: "Pressure regulating valve" need help with what happens at no flow

(OP)
Thank you all for the good advice. I will let you know how it ends up

RE: "Pressure regulating valve" need help with what happens at no flow

(OP)
Update: We tested system and found check valve does not work at all. We had an expert from a large distributor come in to look things over to make suggestions on new parts. They suggested and will be quoting a
-spring loaded check valve of some design maybe the kind with 2 flaps? not sure.
-actuated butterfly shutoff valves with high temp elastomers - ball valve as alternative
-regulating valve to replace the reducing valve

We think this will put is in a good position. Any thoughts or suggestions?

We will be reviewing all the cut sheets prior to accepting anything

RE: "Pressure regulating valve" need help with what happens at no flow

Thanks for coming back and telling us - too few do that.

Now sounds like a proper system to me. You might still get an initial flow from the relief valve, but should be lower and stop once you close the butterfly valves.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

RE: "Pressure regulating valve" need help with what happens at no flow

(OP)
OK I have narrowed valves to a few options. Some of which are class IV ...

so question - in your experiences is a class IV valve good to prevent pressure from equalizing from one side to the other? I know the description of what that class of valve does and it sure doesn't seem like it would work good here...

"Intended for single port and balanced single port valves with extra tight piston seals
and metal to-metal seats.
• 0.01% leakage of full open valve capacity.
• Service dP or 50 psid (3.4 bar differential), whichever is lower at 50 to 125oF.
• Test medium air at 45 to 60 psig is the test fluid."

So if there is 120GPM water should you expect some amount up to 1.2GPM to leak by? Assuming less since the test medium was air.

Or should I be looking for strictly class VI? Thanks

RE: "Pressure regulating valve" need help with what happens at no flow

It's 0 point 01 percent of max flow, i.e. 120 x 0.0001 = 0.012 GPM

Class IV is pretty good and should do fine for your purpose, but as we've all said a lot of times before control valves are not as good at isolation as isolation valves. Horses for courses and all that.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

RE: "Pressure regulating valve" need help with what happens at no flow

Since the regulator is not tight shutoff, the downstream piping will always equalize at upstream pressure if there is no leakage or return path from the downstream system. Usually a small return path to the low pressure side of the upstream system will solve the problem, then the slight leakage thru the regulator has some place to go before pressure builds up.

The only way to get absolute system isolation is with double block and bleed arrangement, not practical for many applications.

An rule often overlooked in fluid system design: The fluid system must be designed to operate satisfactorily with valves that leak, or with valves that do not leak. Good engineering practice generally dictates this rule be followed.

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