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Barrel sealing piston

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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Barrel sealing piston

Unread postAuthor: rednecktatertosser » Thu May 24, 2007 9:43 pm

I am about to start making a barrel sealing piston valve. i have a good understanding about how they work, any and all input is still welcomed, although i have one question, would it work to use a return spring so i can have it be filled from the chamber as opposed to behind the piston?
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Unread postAuthor: ShowNoMercy » Thu May 24, 2007 9:46 pm

Yea I dont see why not. But isnt it easier without?
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Unread postAuthor: rednecktatertosser » Thu May 24, 2007 9:48 pm

well, all it involves is adding a spring and a guide rod. so i dont really think its making it that more compex

Merged:

thank you for your input though
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Unread postAuthor: ShowNoMercy » Thu May 24, 2007 9:50 pm

Actually yea I see your point on that. Good luck with your project and let us know how it turns out. How big are you making it?
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Unread postAuthor: rednecktatertosser » Thu May 24, 2007 9:54 pm

thanks. its gonna be in a 2" tee and im using a 1.5" endcap with a neoprene seal as a piston. and ill be sure and post it. i need to get some damage pics of the cannon i built today after everything sets and then ill post it. look for some cannons from me over the next couple days/weeks

Edit: oh and its gonna have 2" chaber porting and 1.25"barrel porting
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Unread postAuthor: noname » Thu May 24, 2007 10:16 pm

You don't need a guide rod for a spring pushed piston, just drill a hole the same size as the spring in the piston (if it's solid). If your piston is an end cap, fill it with expanding foam or something to reduce pilot volume and then drill a hole in it for the spring. I did this, except the piston is a pill bottle filled with Bondo.
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Unread postAuthor: rednecktatertosser » Thu May 24, 2007 10:30 pm

hmmm... thats a really good idea. so would great stuff be acceptable? or should i fill it with bondo?
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Unread postAuthor: noname » Thu May 24, 2007 10:34 pm

Great Stuff is some kind of expanding foam, isn't it? If so, yeah, it'll work perfectly. Bondo gets pretty heavy if you use enough, so the piston will be less massive if you use Great Stuff.
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Unread postAuthor: rednecktatertosser » Thu May 24, 2007 10:37 pm

ok. well i guess ill be getting some great stuff tomorrow along with some neoprene, some o rings and a spring.

and thank you all for the advice.
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Unread postAuthor: userjjb » Thu May 24, 2007 11:19 pm

rednecktatertosser wrote:thanks. its gonna be in a 2" tee and im using a 1.5" endcap with a neoprene seal as a piston. and ill be sure and post it. i need to get some damage pics of the cannon i built today after everything sets and then ill post it. look for some cannons from me over the next couple days/weeks

Edit: oh and its gonna have 2" chaber porting and 1.25"barrel porting


Three things:
First, a 1.5" endcap will not fit without significant sanding, however a 1 1/4" endcap will fit damn near perfect.

Second, unless you want 1 1/4" outlet porting specifically for some reason, you can actually have your outlet be 1 1/2", there'll be enough of a size difference for your piston to actuate, and because the diameters are closer together, it will actuate quicker. Not too mention you'll get noticeably better performance with a larger outlet.

Third, if you are going to use fittings for a piston I have 2 suggestions. Make sure you have a decent bumper for the piston as Type 1 PVC is quite brittle and cracks easily. I had no trouble with my old piston in my launcher with no bumper, but when I tried out a new piston made out of fittings, it cracked after several shots. Now that I added a bumper it's survived almost 250 firings without a hitch. Second, it's very easy to add an o-ring and a check valve to your piston and get superior performance. To see how I did it, check out a very similiar luancher I made: <a href="http://www.spudfiles.com/forums/tibs-launcher-new-piston-t7933.html">TIBS Launcher</a>
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Unread postAuthor: rednecktatertosser » Thu Jun 21, 2007 11:33 pm

Ok well seeing as i used an unsanded 1.5" endcap as a piston i think you are wrong.

Now i have another question. While making a serviceable piston does the oring groove on the back plug have to be on the piston ise of the screws or not?
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