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New to Pneumatics :(

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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Unread postAuthor: Hawkeye » Sun Nov 25, 2007 6:33 pm

I'm sure it could be done in the UK for under 50. There is the notion that you HAVE to use a qev to either exhaust it or as the main valve. Plus the ball valve safety etc.
I'm pretty sure you could do a simple over/under piston gun with a threaded fitting to access a piston and a presta to fill and exhaust it (or a blowgun).
There is a whole lot of extra on an average UK spudgun that really isn't necessary if you're not getting up to ridiculous pressure.
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Unread postAuthor: Ragnarok » Sun Nov 25, 2007 7:17 pm

@Hawkeye:
It would be possible to build a piston valve for a little less, but piston valves are not the simplest of things to do, and having built 10 of them in these sizes, I have a good idea.

@furball:
It's not all from the same store, but there is no one store I know of that supplies absolutely everything. There's three different net stores, parts are sourced as best as I can to keep costs down.

I'll do a complete write up of the plans and post the lists tomorrow - for one thing I'm a little tired and I'm sure you'd prefer I didn't make mistakes.
I'm also in the middle of re-writing a range calculator spreadsheet someone left me to do.
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Unread postAuthor: Hawkeye » Sun Nov 25, 2007 7:21 pm

Piston valve: A bolt with a stack of tap washers and a neoprene washer. How hard is that? Yes you can tweak them and fit one way valves in them but the equivalent of a leaky cork that seals the barrel is perfectly adequate.
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Unread postAuthor: Ragnarok » Sun Nov 25, 2007 7:47 pm

It's not impossible to do your first piston valve well, but sealing against the end of a copper pipe is not easy. I have had sealing faces cut clean through by the forces concentrated around the low area, and they always need a little maintenance.

As I have enough experience building such valves with the materials and limitations of the UK, I say with complete honesty, it is not something I would recommend to a newcomer to the hobby.

A 3/4" QEV is much simpler, more reliable, essentially maintenance free and not actually that much more expensive - only a couple of quid, because the QEV doesn't need a second size of pipe to complete the valve.
The benefits outweigh the costs by a huge factor. ~£2 for a more reliable, easier and probably better valve sounds like the way to go to me.

I thought it through very carefully, and made the decision based on all the facts. I'm actually rather offended that you are suggesting I might be trying to deliberately mislead furball - I would do no such thing.
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Unread postAuthor: Hawkeye » Sun Nov 25, 2007 8:02 pm

Get over it. Perhaps you just needed to make the copper smoother or the sealing face harder. I always glue a copper reducer to the pipe that the sealing face meets. Not a significant reducer that will choke flow
but really just because reducers are thicker walled and that makes the edges less prone to cutting into the seal. If the seal is backed by several layers of hard rubber rather than a metal washer, it will have that slight give that makes it less like a cookie cutter.
The pipe could even be capped and then have a hole drilled through it to provide a smoother, flatter sealing surface.

I have several pistons that have had well over 300 psi behind them and none have been cut through. Even if they had they are backed by hard rubber washers that will easily take over the job.
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Unread postAuthor: Ragnarok » Sun Nov 25, 2007 8:11 pm

Ok then, if you want to be a smartarse - you make the design then. All UK components of course.
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Unread postAuthor: Hawkeye » Sun Nov 25, 2007 8:22 pm

There is no need to "make the design". There are many on here already that can be copied.
Nothing I wrote was being a smartarse. I'm just saying that you can minimize the materials used.
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Unread postAuthor: Ragnarok » Sun Nov 25, 2007 8:37 pm

Trust me on this, I've looked into it quite deeply, looking at piston valves, QEVs and even sprinkler valves (but that one didn't go far), and I don't think there is a much better choice.

Given that furball doesn't want to complicate things, why use a piston valve that is only fractionally cheaper but undoubtedly more work?
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Unread postAuthor: jackssmirkingrevenge » Mon Nov 26, 2007 12:01 am

and by the way, there's a forum where no one will mind if you're English ;) (not that we mind here y'know :P :wink: )
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Unread postAuthor: furball » Mon Nov 26, 2007 2:59 am

Ragnarok, I really appreciate your help here.


Thanks
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Unread postAuthor: jrrdw » Mon Nov 26, 2007 6:14 am

I didn't catch your spending limit untill i posted earlier, that being said. Did you get a look at the launcher being sold at www.bcarms.com.
This one. But check this kit out he started selling since i last visited the spudfile store Pneumatic kit, Combustion kit.

Arn't the kits rite in your spending range?
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Unread postAuthor: Necrosis » Mon Nov 26, 2007 7:27 am

Zen/// wrote:
I could buy a real air rifle (1000 PSI) for that!


HA!
http://www.glbarnes.com/Nebula_2.html
5000$
A REAL air rifle.



I am sorry to inform you that that is one ugly gun...

http://www.glbarnes.com/yukon2.html

That one made by the same guy is much prettier. :3
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Unread postAuthor: Ragnarok » Mon Nov 26, 2007 8:29 am

jrrdw wrote:Arn't the kits rite in your spending range?

Not really, commission and international shipping totals up quite quick.
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Unread postAuthor: furball » Mon Nov 26, 2007 10:28 am

A UK delivary of a PVC ball valve is £10..

I pay £3 for the ball valve
£2 and a bit for VAT

£10 for delivary!

I hope the delivery here is quick and not expensive :\
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Unread postAuthor: Ragnarok » Mon Nov 26, 2007 10:47 am

Is that from Pipestock? They're notorious for their delivery costs.
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