Pressure regulating valve

[escapadro]

Hi gentlemen, I'm new to this forum!

I have a question regarding a PRV. There is an existing line of pressurised air that is planned to be divided at one user point into two. One branch will be reducing pressure to 2, and another should stay at 6. Now, is there a PRV, that will be pre-set to reduce the bar from 6 to 2 and lock, but also have a possibility to be manually closed from 2 to 0? At the end of the day, operator should be able to come up and close the valve, shutting down the process.

Maybe there is some sort of a PICV that could do that?

Thanks in advance!

If pictures of the process are needed, I may be able to provide them for further help.

Cheers!

 

[LittleInch]

What's wrong with an isolation valve right after or just before the Pressure regulating valve going from 6 to 2??

BTW PRV is often confused for Pressure Relief Valve so much better to use full words sometimes to avoid confusion.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[escapadro]

Hmm, I suggested the same solution, I guess the client is trying to save space and money!

But, out of curiosity - is there a valve, that can do a two-step job like I described? I've seen a similar setup in a Quality Lab, where they didn't want to see 6 bar, so on the inlet, there indeed was 6 bar, reduced down to 2 bar with further hand-adjustment possible (hand dial) between 0-2 bar downstream.

I may be wrong and they just had a block containing two valves, but if I'm not imagining it - could someone shed some light on that idea?

Regards and thank you LittleInch!

 

[LittleInch]

Yes, Most regulating valves are adjustable down to zero, but it's a strange way to use it and many regulating valves will have difficulty sealing if you do this operation a lot. Their job is to regulate not isolate.

There are many many regulators on the market so you will find one to meet your requirements.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[escapadro]

That's perfect, LittleInch.

So this mysterious PICV that entails both isolation and pressure regulating jobs isn't desirable if shutdown (i.e closing of the valve) is done frequently?

I also wonder if my P&ID show PICVs as Pressure Indicator Control Valve or Pressure Independent Control Valve... confusion.

Thanks, LittleInch!

 

[LittleInch]

Well, if you have instrument air that's clean then you might find a high quality valve which allows this, but in general its better to use a regulating to regulate and an isolating valve to isolate. Depends if your users don't mind the valve hissing a bit after a while. If you use a cheap regulator then expect this sooner rather than later.

PICV to me would be Pressure INDICATING Control Valve, i.e. it has pressure gauges on it....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[escapadro]

Hmm... I'll suggest it to them. I'll look into those high quality valves that can do both at the same time, but it does make sense to separate both jobs. Even for maintenance of the PRV. How come regulators aren't that great at isolating? Surely they should handle being fully closed? Sorry, piping and valves isn't my main area of expertise!

 

[zdas04]

Don't do it. The cost of leaked air will exceed the cost of a simple ball valve within weeks. Put a floating ball valve on the high-pressure side of the regulator and shut it instead of adjusting the regulator. Reasons are:
[ol 1]
[li]No throttle valve (especially the very expensive ones, their extra cost comes from precisely matching a flow profile at near-zero flow and maximum flow) can ever be relied upon for bubble-tight seal. They just are not designed for it. The seats are designed to allow flow even when very nearly closed, that design will rarely be consistent with zero flow. If one happens to give you a bubble-tight seal once, you have no assurance that it will repeat that performance the very next time it goes to shut.[/li]
[li]You do not want your operators adjusting the regulator to zero and then back to target pressure, the cost in labor will rapidly exceed the cost of a block valve.[/li]
[/ol]

Expecting a regulator to shut off flow will always be a false economy.

[bold]David Simpson, PE[/bold]
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

 

[escapadro]

This is what I'm talking about. More I read from you, guys, more I'm convinced to stick to isolating before the PRV.

I attached a part of the process. Yellow line is kept at 6 bar (supplying line is already at 6 bar, but fluctuating, so PRV to maintain preset pressure with possibility of regulating between 6 and 2). And the blue branch (proposed tie-in) to be kept at 2 bar with possibility of reducing to 0. What's bubbled is a proposed branch, but I don't see why they want to tie-in so far upstream. We could easily soft-connect the tie-in at the flange in UL-51697 (inside the room, where two air drops are required).

Thoughts, gentlemen? I think valve question has been answered. Manual floating ball valve before the PRV with an indicator.

 

[escapadro]

I'm just pinning the thread back to the top. Hopefully someone can give me some insight into what they're suggesting.

 

[GD2]

Escapadro,
The P&ID just looks fine to me except that the second PCV set at 0-2 bar need to be a manual one instead of self-regulating. In my experience a self- regulating valve can't regulate to 0 bar. If the designer, don't have a symbol for manual PCV, they should specify 'Manual' at the bottom of the valve.
The P&ID is not a dimentional drawing. You need to see the Isometrics to figure out how far the tie-in is outside the building.

Ganga D. Deka, P. Eng
Canada

 

[lilliput1]

Why bother shutting off branch valves? Leaks? Fix leaks. Let compressor cycle on/off. operators should make sure their local air outlet off at end of day.

 

[escapadro]

The only problem I have is that this branch tie-in could be done inside UL-51697. Why do they want to tie so early before the room? Room = further purification, outside the room = initial purification. Maybe they need to ensure the pressure drops BEFORE the process proceeds on to the next stage? I think the set-up mentioned by zdas04 is the most sensible, but I'd do it INSIDE the room. Saves money and space.