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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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Valves

Unread postAuthor: WOW!! » Fri Aug 11, 2006 3:24 pm

Iam makeing a new cannon 76" of 4" pipe. I am going to do a over under desgin with a 10' 2'' barrel. I wanted to make a piston valve but to much money. So I was going to go with eather dual sprinkler valves(Should I use 1 1/2 to the vavles or 2'' pipe?)Or ball valves. For the sprinkler valves I was going to use 5/8" NPT fittings for a little extra air flow. What should I use?
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Unread postAuthor: Velocity » Fri Aug 11, 2006 3:43 pm

too much money for a piston valve? Well consider this: the flow of MOST sprinkler valves is equal to that of a 9/16" hole. Two spirnkler valves cost $25 (at minimum). For $30, you can build a piston valve with a 2" opening and a full 1.5" port (with parts bought off of mcmaster; that valve has greater than 5X more flow than dual sprinkler valves

But if you are really against building a piston valve:

Don't use ball valves; you will not be impressed with the performance; go with the dual sprinkler valves. Because theis will be a dual chambered gun (or at least I suppose so, because there are dual valves), make the two sprinkler valves connect in a 1.5" tee, which then leads to the barrel
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Unread postAuthor: WOW!! » Fri Aug 11, 2006 3:46 pm

It is a single chamber with 2 vavles. I have made valves but havent had good luck with them that is why I was going with the sprinkler valves.
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Unread postAuthor: ProfessorAmadeus » Fri Aug 11, 2006 3:47 pm

well dont use the ball valves because thats a waist of time unless you have a device like a pnuematic arm to open it. dual springkler valves will possibly not dump the air fast but its better that a ball valve. explain why a piston would be to expencive.
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Unread postAuthor: WOW!! » Sat Aug 12, 2006 10:56 pm

The way I was going to do it was with solid PVC and all that stuff, but there is mechineing, bying the stock, orings and all the parts. But I found a cheaper way to make it so I am going with a single piston valves, 4" in 4" out.
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Unread postAuthor: mark.f » Sun Aug 13, 2006 7:05 am

A simple barrel sealing piston doesn't need O-rings. It just needs to fit good enough so that equalization is slow enough to actuate properly.

Just build the piston from moulding epoxy, fiberglass resin, hot glue, etc. No need to buy solid PVC rod. Just use your common sense though, weaker materials won't stand up that long.

If you still want to use O-rings, (hey, it gives more controllable equalization...), you might want to consider something I'm working on. For my barrel sealer, I'm just gonna extend the edges of the gaskets, (one on the front and back), past the edges slightly, (just slightly), with the gaskets securely glued and fastened to the piston faces, so that they act as a seal. I figured since BurntLatke pretty much used this idea for air-tight gasket slugs, it might work. If not, oh well. It's barrel sealing, and it's going to be exhausted by a 1/4" QEV. It's a double-seal, (front and back), also, so I think it has a good chance of working.

You can't just use the inside of a soccer ball for this sealing material though! :o Order some neoprene sheeting off McMaster if you consider this idea.

I get all my junk in Monday, (I forgot UPS didn't deliver weekends, so I ordered on Friday), so if you want to wait a week or so to see if I can get it to work, go ahead. I'll share results when I finish the cannon.

Here's what I'm talking about.

<img src="http://i10.photobucket.com/albums/a123/markfh11q/gasketseal.png">

If this works, (and is completely airtight), I might use it on a chamber sealing valve to finally eliminate O-rings!!!
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