"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

 

[hacksaw]

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.

 

[zdas04]

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

 

[USAeng]

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.

 

[zdas04]

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

 

[USAeng]

Thank you. Good article

 

[LittleInch]

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

 

[USAeng]

Here is the check valve in use - see attached

 

[zdas04]

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

 

[LittleInch]

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

 

[USAeng]

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

 

[USAeng]

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

 

[LittleInch]

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

 

[USAeng]

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

 

[LittleInch]

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

 

[FredRosse]

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.