"Pressure regulating valve" need help with what happens at no flow 1

[USAeng]

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

 

[racookpe1978]

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?

 

[GHartmann]

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?

 

[zdas04]

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

 

[LittleInch]

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

 

[GHartmann]

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.

 

[USAeng]

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?

 

[hacksaw]

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?

 

[LittleInch]

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

 

[LittleInch]

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

 

[USAeng]

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

 

[USAeng]

Pic1

 

[USAeng]

Pic2 ARI valve.

Pic1 was the secondary loop pump

 

[USAeng]

Thermal heater and supply/return from the secondary loop

 

[LittleInch]

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

 

[USAeng]

Yes it does. Thank you

 

[hacksaw]

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...

 

[zdas04]

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

 

[LittleInch]

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

 

[LittleInch]

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/750001-2.pdf

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