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Ball Valves

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Ball Valves

Unread postAuthor: Spooky » Mon Nov 30, 2009 4:40 pm

Hi guys, after seeing all of the wonderful large bore sawed off style pneumatics about recently I thought I'd give one a go myself.

Looking at a ball valve to pilot this is cheap and there's a screwfix 5 minutes drive from me. Now, there's no pressure rating with it so I was wondering how high I could safely run a lump of brass like that? Also, I don't have a huge amount of faith in compression fittings so could I use sandpaper to expose the brass, flux it up and solder it to the copper pipe like normal?

I just don't know if it would bond properly.. or if there are components to the ball valve that would be damaged from the heat for that matter.

Cheers
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Unread postAuthor: MRR » Mon Nov 30, 2009 4:55 pm

The internal seal in the ball valve (which is made out of plastic) could melt and cause the valve to leak or it will be hard to operate.

You should buy a "normal" threaded ball valve and solder a suitable fitting to the pipe, so you can simply screw them together.
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Unread postAuthor: jackssmirkingrevenge » Mon Nov 30, 2009 4:56 pm

It's rated for steam so will likely be able to take 500 psi+ comfortably. You don't want to heat the valve too much though.
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Unread postAuthor: Biopyro » Mon Nov 30, 2009 4:57 pm

You wouldn't be able to solder that, but compression is VERY trustworthy.
That will likely take 18 or 24 bar - higher than you'll ever take it as a beginner.
On the valve will be written PN18 or similar. This designates the pressure rating in bar (PN18 is 18 bar etc)

You can put together a very good simple cannon with very few parts if you're good at soldering, so get yourself an andcap and maybe some elbows and get going!

This was my first copper pneumatic. Served well for getting me into it, and was very simple to build, especially as you have soldering experience.

Check out the UKSGC. There are more UK specific cannons, and a forum just for UK suppliers. Mostly local suppliers are good for such common parts, but Toolstation, BES ltd and as you pointed out, Screwfix have very competitive prices, and Toolstation's delivery policy is great.
Steer clear of the UKSGC shop, it's unreliable at best, and since the owner has no internet at the moment, no orders are going through.
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Unread postAuthor: Spooky » Tue Dec 01, 2009 6:10 pm

Thanks for the feedback. The PN** rating was something I wasn't aware of. I've already used a 15mm version of the same BV in another cannon, looking at it now I can see a previously meaningless PN32 marking on it :)

I was hoping to take this cannon up to 400PSI to make up for the short barrel and chamber. I think I've gotten reasonably good at soldering now so the only join I'm concerned about is that to the ball valve. If I spread some epoxy on the end of then pipe then tighten the compression fitting it should be enough to give me peace of mind.

I'll post some pictures before I take it that high anyway if that's OK. I've only been to 200PSI before :wink: .



Also, hijacking my own thread.. Could I get some help modeling a QEV like the 3/4" here in GGDT?

I've read the documentation on GGDT but didn't find it terribly helpful, for example the Seat Diameter is described as "the diameter of the seat" or something. I know exactly how the valve works it's just what the wording refers too.

Cheers
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Unread postAuthor: Biopyro » Tue Dec 01, 2009 6:18 pm

Here is a quick guide written by Ragnarok. It goes through what things mean in GGDT and has sample values for UK QEVs.

Definitely post some pictures!

If you have the knowledge to take a cannon to 400psi, I trust you know how to take advantage of it? (ie. something faster than a ball valve) Sounds good though, we look forward to seeing the results!
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Unread postAuthor: Ragnarok » Tue Dec 01, 2009 7:42 pm

Biopyro wrote:You wouldn't be able to solder that, but compression is VERY trustworthy.

Agreed - compression fittings, if done to spec, are solid pieces of kit.

Still, I am in the habit of carefully* soldering olives in place in some cases, because it allows one to avoid having to crush the pipe down so much (good when flow is critical).
I wouldn't do it in a pilot, flow isn't crucial enough, but something in the way of the main airflow in the cannon - probably.

*Carefully, so that solder isn't somehow preventing the compression seals working properly.
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Does that thing kinda look like a big cat to you?
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