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Metal Piston Valve Questions

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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Metal Piston Valve Questions

Unread postAuthor: cwazy1 » Mon Dec 10, 2007 11:44 pm

So I am making an all metallic pneumatic cannons at which the opperating pressure will be 200psi. it has a copper 1" chamber thats 34" long and has a chamber volume of 25cu-in. the barrel is a breech loading alum, marble barrel. now, i have everything except for the valve.

so i first decided on buying a qev. and i actually bought a 1/2" qev. then having not even received it yet, i was surpassed by the idea of making a 1.5" piston which would yeild much grreater increase in power.

so what im planning is a 1.5" all threaded black steel tee as the main valve body. then, i will cut a piece of 1.5" sch40 galv steel pipe to fit inside the tee as the real piston housing (the reason i use this is because it fits near perfect to the actual diameter of the tee). then, i will take that piece of pipe, and jbweld it to the metal bushing on the pilot side of the tee. this will create an airtight place for the incomming air to push the piston. afterwards, on the barrel side of the tee, i'll have a pvc bushing from 1.5" thread to 1" slip. i'll have this bushing be a modded bushing so i can have the 1" pvc sticking into the tee for where my piston's sealing face will make contact.now thats my housing things, the piston iteslf i will cast a mould using epoxy, and will be casted inside the 1.5" galv pipe so it fits perfectly. then i'll drill a hole through, amke a sealing face and bumper and yeah all the extras. and well im thinking, i am prolly not going to use the qev for piloting the piston because the qev is only rated for 150psi. and instead, i'll use a .5" ball valve. ......so heres my drawing, hopefully you can understand.

give me some feedback, thanks!

Image

EDIT: something weird happened to the pic..just click on it for a clear/fullsize view.
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Unread postAuthor: jackssmirkingrevenge » Mon Dec 10, 2007 11:57 pm

looks like it should work, might I recommend a good look at my casting epoxy pistons tutorial if you have no experience with epoxy.
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Unread postAuthor: octane89 » Mon Dec 10, 2007 11:59 pm

I forget who but someone made a steel cannon from all two inch, and had a tee valve along with co2 setup. He ran it at 300psi i think, so I believe your idea will work just fine.
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Unread postAuthor: cwazy1 » Tue Dec 11, 2007 12:01 am

ahh thank you jack, i've never thought there was a topic on that =Dand is white lithium grease okay to use as the lube in casting the epoxy??
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Unread postAuthor: jackssmirkingrevenge » Tue Dec 11, 2007 3:24 am

yes that should do nicely.
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Unread postAuthor: Infernal Maveric » Tue Dec 11, 2007 4:03 am

QEVs that are rated to 150PSI will be fine at 200PSI. It would yeild better performance over a 1/2" ball valve.
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Unread postAuthor: cwazy1 » Tue Dec 11, 2007 11:31 pm

yeah thats what im thinking i'll do. im prolly not going to build another cannon, so i'll just stick it on there.

so update, i built my piston today, pretty hefty, pretty damn heavy. im using a end cap as the piston right now cuz i dont have any epoxy atm, i'll post pics in a little bit.
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