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Help designing piston valve

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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Help designing piston valve

Unread postAuthor: bl74 » Fri Jul 24, 2009 2:49 pm

Hi im planning on making a gun with a piston valve soon. My first pneumatic was a dual 1" sprinkler valve setup but it leaks and doesnt fill up anymore. I want to build a new one with even more power so im gonna try to make a piston valve out of a tee with a over/under setup. I was planning on using a 3" tee and 1.5" barrel extending into it that the piston would seal against, but then i saw that most 3" piston valves had 2" pipe in them to seal against the piston. Would 2" pipe outlet give a significant performance boost even if I still used a 1.5" barrel? If not I guess i might as well make it out of a 2" tee, but does a 2" tee with 1.5" outlet perform the same as a 3" tee with 1.5" outlet? Also, i want to make the piston serviceable without drilling screws around the pilot side of the tee that would have to be removed. What parts would i need? I'm planning on using a modded sprinkler valve as a pilot. The valve on this gun would be a good example - http://www.spudfiles.com/forums/viewtopic.php?t=4365
And one more question- How would you be able to glue the barrel so that it extends into the tee without getting glue and primer all over the pipe that you have to push through the bushing?
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Unread postAuthor: mark.f » Fri Jul 24, 2009 3:40 pm

A 2" tee with a 1-1/2" outlet (assuming SCH-40 pipe and fittings) will open faster than a 3" tee with a 1-1/2" outlet. Also, the pilot volume will empty more completely before firing, but depending on the piston's seal, this could be variable.
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Unread postAuthor: beardie6767 » Fri Jul 24, 2009 3:44 pm

I'm still new to piston valves as well, but i fell i may be able to help, so i'll voice my opinion.

I'm not too sure about what size pipe will give you the best performance, so i'll leave that for someone else (sorry!)

but what i did to get my barrel through my reducer (in your case a tee) in my piston cannon was sand off the lip that usually stops the pipe from going in too far, push it part way in so you're about an inch or so from where you want the connection to be, then just prime and put glue like you normally would on the area where your pipe will be inside the tee.

i hope this helps, and if you need my to explain it better let me know.

good luck with your cannon!
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Unread postAuthor: jor2daje » Fri Jul 24, 2009 3:54 pm

heres how i did that

link
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Unread postAuthor: jrrdw » Fri Jul 24, 2009 4:05 pm

jor2daje wrote:heres how i did that

link


Thats a really good diagram of a piston valve built into a tee. Good work! :D
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Unread postAuthor: Technician1002 » Fri Jul 24, 2009 4:12 pm

jrrdw wrote:
jor2daje wrote:heres how i did that

link


Thats a really good diagram of a piston valve built into a tee. Good work! :D


The only important thing left out is the bumper to prevent cracking either the piston or pilot area. Other than that, it's a fantastic drawing. These high speed valves will beat themselves to death if you let them.
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Unread postAuthor: jrrdw » Fri Jul 24, 2009 4:18 pm

Thats a good catch Technician1002, I was impressed enough with it to over look that. Make sure you add that bl74.

Welcome to Spudfiles.
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Unread postAuthor: bl74 » Fri Jul 24, 2009 5:00 pm

Thanks jrrdw. jor2daje that diagram helps a lot, im gonna put the outlet pipe in through the tee pushing outward and then glue on the female thread adapter. That way no glue gets where it shouldn't be, plus i wanted to have removable barrels anyway. And what you show on the pilot side is exactly what i was thinking to make it serviceable. Im thinking im gonna do exactly whats shown there except scale it up to a 3" tee with a 2" outlet since that obviously has more flow than a 2" tee with a 1.5" outlet. Thanks
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Unread postAuthor: Technician1002 » Fri Jul 24, 2009 6:16 pm

I though I would toss in a little of what to expect. I had an orange go bad, so I disposed of it by recycling it into a fine mist for the garden. As long as I was recycling, I decided to add some water. I had an empty milk jug that needed recycling.. Playtime :D

2 inch piston in QDV configuration, Milk jug full of water, add 70 PSI air and mix well. :D

Found the impact point punched a nice circle into the side of the jug. This is what I call a shot right in the cookies. :D

The explosion got everything wet within 20 feet in all directions including me. I need to back off a little.
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OrangeMilk.jpg
recycled milk jug and the next orange ready for recycling Note nice round orange shape patch.
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