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2.5" piston valve help

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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2.5" piston valve help

Unread postAuthor: LCTChamp » Wed Mar 25, 2009 5:45 pm

Well my 2" sprinkler valve on the 2SVGBG ( the gun is here http://www.spudfiles.com/forums/finnaly-the-2svgbg-t17632.html) quit working and I haven't built a piston valve yet. So I decided to build a 2 1/2" piston with 2" porting. My hardware store had 2.5" sch. 40 conduit fittings. Can 2.5" conduit be safely used with 100 psi? If not I will order the appropriate fittings online. I noticed 2" pipe fits reasonably well and only needs a few wraps of tape to fit well. Can a piston made with 2" pipe seal well against a 2" barrel? Would the piston be safe if I filled it with hot glue or do I need to fill it with epoxy?


Thanks for any help in advance.
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Last edited by LCTChamp on Wed Mar 25, 2009 6:04 pm, edited 1 time in total.
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Unread postAuthor: jmeyer1022 » Wed Mar 25, 2009 5:58 pm

I believe the conduit will be fine, I'm not positive though, in my 2" cannon I use a 1 1/4 coupling as a piston and it seals against a 1 1/4" coupling so you should be ok there. Filling the pip with epoxy/hot glue a little would be a bad idea, doing the whole thing would have to much mass.
What I did was:
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I used "welder" its an epoxy, to hold the washers to the piston better and seal so nothing got inside. It hold's great.
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Unread postAuthor: LCTChamp » Wed Mar 25, 2009 6:05 pm

Thank you! I will use your idea. Anyone know for sure if I can use conduit with 100psi?
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Unread postAuthor: mark.f » Wed Mar 25, 2009 8:37 pm

I want to say that conduit is cellular core, but you should check that. If it is, then it would be a mistake to use it in a pneumatic.

2" porting is a little more confusing than using 1-1/2" or below in a 2" tee, or 3" in a 4" tee, because there are not a lot of things that fit into 3" pipe. 2" SCH-80 fittings fit well, but not well enough.

I say try using a 3" tee instead of the 2.5" one, though.
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Unread postAuthor: Carlman » Wed Mar 25, 2009 8:40 pm

mark.f wrote:I want to say that conduit is cellular core, but you should check that. If it is, then it would be a mistake to use it in a pneumatic.


as did I but wasnt sure
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Unread postAuthor: jrrdw » Wed Mar 25, 2009 9:19 pm

The problem with your plan is you wont have any surface area on the outside of the barrel for the air to push the piston back. It still might work but the performance will be bad.
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Unread postAuthor: LCTChamp » Thu Mar 26, 2009 6:04 am

The problem with your plan is you wont have any surface area on the outside of the barrel for the air to push the piston back. It still might work but the performance will be bad.


That is what I was afraid of. Well I guess I'll have to order fittings online. Back to the drawing board!
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