Hi everyone, I am routing underg

[inertia1]

Hi everyone,

I am routing underground pipework for a DN350 compressed air pipeline @10-13bar. I need to install several isolation valves along its length. Firstly what type of valve would you reccomend?

I have been advised that a ball valve would be most suitable, does anyone know of any suppliers (UK & Europe) that manufacture ball valves at this size?

Thanks

 

[bcd]

Hello,

A ball valve would work very well. There are several manufacturers that make them this large, and the price will be relatively high. An internet search under large ball valves will get you different suppliers. For UK and Europe, Neles, Jamesbury, PBV come to mind. A gate valve will also work but is more likely to leak and you will have the issues with a rising stem underground. My recommendation is to look at a high-performance butterfly valve. Tight shut-off, less torque to operate, less cost, and is more readily available.

bcd

 

[zdas04]

To specify a block valve for a pipeline you need to specify:
- Fluid (you said air)
- Pipeline material (maybe the DIN spec is specific)
- Pipe size (you didn't say)
- Pressure (10-13 bar)
- Temperature (you didn't say)
- Volume flow rate (you didn't say)

For someone to suggest "use a butterfly valve" (or a gate valve, or a plug valve, or a globe valve, or even a ball valve) without all of this information is pretty irresponsible.

There are many situations where a butterfly valve is the best choice. I've never seen a "pipeline" that was one of those situations. Inside pipelines you accumulate compressor oil, condensed liquid, pipe scale, and corrosion products. Eventually every pipeline will accumulate this crap to the point where pressure drop becomes a problem and the operator considers pigging the line. With butterfly isolation valves located periodically through the line, you can't pig it and in a rational world the designer should be in serious trouble (in the real world he has changed jobs 4 times before his stupidity comes to light).

If the flow is really high velocity then the plate of a butterfly valve protruding into the stream will create Von Karmaan Vortex Streets that exert a very large force on the bluff body (plate) and can set up vibrations that have destroyed plates.

Please provide enough information to allow a rational discussion.

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

 

[CountOlaf]

zdas04: You made some good points in that tirade, however, I'm pretty sure that DN350 is the pipe size--think "dimension nominal" for DN and 350 is mm, so I believe the thread creator was referring to 14" pipe. They probably use this nomenclature in Europe etc. as implied.

 

[zdas04]

The "tirade" was directed at the guy who said that the OP should use a butterfly valve without knowing wat the conditions were.

David

 

[CountOlaf]

True enough, zdas---like you said, pigging is a little more problematic with butterfly valves .

I didn't even know they made ball valves that large! I don't see the issue with gate valves brought up by bcd. They use NRS gate valves pretty universally at least in fire protection water loops and the like. That's why we have all those valve boxes near each fire hydrant.

 

[dcasto]

All of the valves should have a riser stem to bring actuation above ground if needed. With air a vault's only drawback would be water inflow into it.

The OP has to decide if the line needs to be piggable, but if it doesn't, I'd vote on a butterfly valve in a vault.

 

[zdas04]

The OP hasn't been back on eng-tips.com since he posted this. He probably didn't really want an answer.

CountOlaf,
The biggest ball valve I've ever seen is 60-inch, but I know there are bigger valves out there. 14-inch ball valves are pretty much shelf items these days.

Dcasto,
I can't tell you how often I've had people come to me with butterfly valves they put in cross-country lines because "they'll never pig that line" and then realized that they're accumulating condensation in the line and want to pig it. My response is always "sorry, you've got to replace those inexpensive butterfly valves with something that a pig will traverse." This has happened often enough that I only recommend butterfly valves in places that can't become piggable (maybe compressor bypass, separator inlet, tank isolation). You can put handwheel extensions on any sort of valve, and you can order ball valves with a sealed stem that you can grease from the surface.

David

 

[dcasto]

fair enough Zdas04, I'd hope the air was dried and monitored for dryness. I'd the the OP to return and explain some more.

 

[inertia1]

Thankyou everyone for your comments and advice.

I dont know if this will help but here is some more information...

We have 3 compressor houses serving a ring main system, approximatley 3.5km in total lenght. Each compressor house can produce 15,000 cfm (free/unpressurised air) per comp hse 3 hses. The air will be at ambient temperature for the location - 45 deg C. The compressed air will be used to power tools on site.

I originaly asked the question to see if there was a general code of practice for such installations....it soon became clear that you all have different opinions!

We do have other buried services (water, oxygen etc), for these we have a buried gate valve with extended spindle to ground level. I was advised for the compressed air line to use a ball valve for this serivce (as for other gases).

I am unfamiliar with the term 'pig' or 'piggable' line. I assume you mean the ability to clean and maintain the line? If so, idealy the line will need the ability to be cleaned, what effect does this have on the valve choice? Could you please explain why the valve makes the line 'piggable'?

Ideally we are looking for the 'best' solution to provide a facilty that can easily be maintained and sections isolated with ease. It is my understanding a 'vault' or valve chamber must be provided if a ball or butterfly valve is used, adding cost to the civil works. What would be a cheaper solution?

Thankyou for all you comments so far...I look forward to what else you have to say!

 

[zdas04]

Yes, a "pig" is a chunk of stuff (often foam or some plastic) that is used to clean a line. A line is "piggable" if a pig can traverse it and there is a way to load/unload the pig. Often, people don't install pigging facilities on dehydrated gas lines, while making sure that if the line does need to be pigged in the future you don't have to dig it up. I once designed an air line (6-inch) with a tee at the point it went into the ground and the point where it came out of the ground. These tees had blind flanges (pierced with a 2-inch thread-o-let going to a blowdown valve). With this simple change (replacing an elbow with a tee), the line could be blown down, the upstream blind could be removed to insert a pig and then reinstalled, the pig could be run to the other blind (with the vent open) and when it got in we could remove the downstream blind to remove the pig. The intention was to run this pig every other year so a very cheep solution made sense.

A butterfly valve has a central stem that holds the valve disk (also called a "plate") and extends across the pipe. With the stem and plate within the flow it turns the pipe cross section into two hemispheres and a pig can't negotiate the line.

David

 

[inertia1]

Thanks for the info. Has been helpful.

I assume the line can be 'pigged' with elbows and tees etc in the line? Or does each straight run of pipe have to have the facility to be 'pigged'?

So if this is case the only solution is to have either a gate or an expensive ball valve...?

 

[dcasto]

The elbows should be at least long radius better is 3D. At the tees, you should weld in bars that block the tee and keep the pig running straight. There have been discussions on how to do this on this site.

A ball valve can be buried as lond as you have an extension on the stem and on the grease fittings. Ball vavles require that they be grease lubricated and the grease also helps make the valve seal. You'll need to find a grease compatible with air. Ball valves are typically cheaper than gate valves and only require 90 degrees to open/close.

 

[stanier]

You could always consider a poly pig. This is a viscous fluid that will go around/through anything.

Geoffrey D Stone FIMechE C.Eng;FIEAust CP Eng

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

 

[zdas04]

In my experience, the term "poly pig" has been associated with a solid pig made of polyethylene like at

http://www.girardind.com/polly.htm

A few years ago BJ Services was selling a gel/liquid pig that would ooze through anything, but they required a solid pig before and after it. Is that what you were talking about?

David