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3" Tee 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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Unread postAuthor: tony48 » Tue Mar 08, 2011 8:31 pm

Yes that is the video and thank you very much for the help. I'll go for a piston with o rings. Is there any specific o ring that fits into a 3" tee or am I going to have to search around? And I guess I'll just play around with different pilot venting mechanisms (blowgun, ball valve) until I get something that works
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Unread postAuthor: Gun Freak » Tue Mar 08, 2011 8:45 pm

If your valve is a 3" tee, use at least a 3/4" sprinkler valve if not a smaller piston valve.
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Unread postAuthor: tony48 » Tue Mar 08, 2011 10:11 pm

Gun Freak wrote:If your valve is a 3" tee, use at least a 3/4" sprinkler valve if not a smaller piston valve.


I really don't want to have a bulky sprinkler valve on my gun. Are there other options?

And I need to look up some bumper designs because that's the last thing I need to plan before I can order some HDPE and turn it down and add some o rings. I'd appreciate help if anyone knows of good examples of bumper systems that I might not be able to find. Thanks
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Unread postAuthor: Technician1002 » Tue Mar 08, 2011 10:32 pm

If your piston has low leakege (small EQ) between the chamber and pilot, a small ball valve works fine. I used a 1/4 inch ball valve on my Dragon. It used a 3 inch piston with a 2.5 inch barrel. It was coaxial instead of in a T.
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Unread postAuthor: Crna Legija » Tue Mar 08, 2011 10:57 pm

you can use anything as a bumper, iv seen peaces of hose and even 1/2 a tennis ball
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Unread postAuthor: tony48 » Wed Mar 09, 2011 6:58 am

-_- wrote:you can use anything as a bumper, iv seen peaces of hose and even 1/2 a tennis ball


So do I just wedge that in the back of the tee? I kinda want to do something more sophisticated like neoprene so this valve will last
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Unread postAuthor: Technician1002 » Wed Mar 09, 2011 11:08 am

On most of my cannons I made a spacer to support the bumper so it will last.

The long 3/4 inch PVC pipe and bushing on the end provide a backstop for the bumper. This limits the piston travel and as a result lowers the impact force on the bumper.
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My Mouse Musket did not have one and it had a habit of breaking pistons.
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Unread postAuthor: Gun Freak » Wed Mar 09, 2011 7:50 pm

tony48 wrote:So do I just wedge that in the back of the tee? I kinda want to do something more sophisticated like neoprene so this valve will last

For some, sophistication is non-existant inside the valve :D

What's wrong with a half a tennis ball? They last quite a while. Replacing it is easy, when it gets tore up by the piston.
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Unread postAuthor: clemsonguy1125 » Wed Mar 09, 2011 7:57 pm

My favorite has always been a large spring.
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Unread postAuthor: Gun Freak » Wed Mar 09, 2011 7:59 pm

Big sprinklers have huge springs in them, but they are pretty strong. Perhaps strong enough for a semi auto GB gun :lol:
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Unread postAuthor: Lockednloaded » Wed Mar 09, 2011 8:17 pm

For a three inch valve, a full tennis ball with some holes drilled in it for extra flow would work great
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Unread postAuthor: Gun Freak » Wed Mar 09, 2011 8:21 pm

You're right... yeah get a tennis ball and use a whole saw to drill a bunch of holes all in it for flow.
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Unread postAuthor: tony48 » Thu Mar 10, 2011 6:08 pm

Ok tennis ball it is. Should I use a piece of PVC behind it so that the piston can only move about 5/8 of an inch?
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Unread postAuthor: Technician1002 » Thu Mar 10, 2011 6:15 pm

You do want to limit the piston travel if you don't want it to become a projectile out the back. Use what ever will do the job.

As far as o ring size, find ones that fit the pipe the piston will fit inside.
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There is a how to on using o rings.
http://www.spudfiles.com/forums/how-to-use-o-rings-in-piston-valves-t17899.html
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Unread postAuthor: tony48 » Thu Mar 10, 2011 7:45 pm

Thanks for the great info, links, and pictures. I'm learning alot through posts in this thread as well as searching. One thing I don't understand is if a ball valve is used to vent the pilot, what stops the tank air from rushing out of the back valve? Is the piston supposed to seal off the back half of the tee when it opens?

I'm going to make my piston and housing soon but I still have to decide what to make the piston out of. I've considered wood, HDPE, and a 2 1/2" PVC coupler and I know that HDPE would be best but it's kind of pricey for a piece 3" in diameter + shipping. Would it be feasible to turn a 3" piston out of a solid piece of wood on a lathe? I could also turn o-ring grooves no problem. Then I would just have to add a sealing face and a hole to allow air to pass to the front of the piston area. Any ideas or comments on this plan?
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