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compacting a tee 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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compacting a tee piston

Unread postAuthor: Lockednloaded » Sun Mar 21, 2010 8:44 pm

I'm planning a build that will either use a 3/4" qev, or a piston housed inside a 1 1/4" tee. I have found no local suppliers for qevs, and i already have a 50$ gift certificate to home depot, so i'm really leaning towards the homemade valve. I would like it to be as compact as possible, but can't figure out how you all do it!
i have no problem making a piston valve, its just every time i make one the aesthetics are greatly lacking. I want it to be as compact as possible, with no machining facilities, and threaded connections to the barrel and chamber. So anybody got any good ideas?
p.s. i want it to be primarily PVC, and i don't need help for the fill/pilot area
p.s.s. Sorry gort your valve is too expensive for me, but thats pretty much the model
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Unread postAuthor: deathbyDWV » Sun Mar 21, 2010 10:11 pm

Use one of these!!! http://www.launchpotatoes.com/index.php?act=viewProd&productId=31

edit... I feel stupid. I missed the last ps.

I'll be back with a vid with a tutorial that I saw that'll work for you.

Btw... It's pps not pss
post post script

A second ago I accidentally hit quote instead of edit and double posted. It auto deleted though... It that a new feature?
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Last edited by deathbyDWV on Sun Mar 21, 2010 10:27 pm, edited 1 time in total.
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Unread postAuthor: Gippeto » Sun Mar 21, 2010 10:26 pm

How I made my first...and only...pvc valve.

A tad larger than what you want, but it's the idea that counts... if not the execution of it.

The rear plug is retained by six equally spaced 1/4x20 screws.

The "guide" is made up of an end cap and a coupler joined with a piece of pipe, and solvent welded into a reducing bushing. That "assembly" was then fitted with the vent pipe, and filled with fibreglass resin.
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Unread postAuthor: MrCrowley » Sun Mar 21, 2010 10:30 pm

You know you could always ask Gort if he would trade the valve linked above for the $50 Home Depot voucher haha. He probably shops there a lot.

He bolts the back plug on as you can see and i'm pretty sure he uses a machine to make the o-ring groove for it. It is possible to do it without a lathe or such but it's a bit tricky.

You basically have to make a line around the circumference of the plug fitting and use a hacksaw, file or dremel to carefully make a groove for an o-ring.
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Unread postAuthor: mark.f » Sun Mar 21, 2010 10:43 pm

A good thing to start with is... a plan.

Know the parts, in general, you need, measure them accurately, and draw up a plan to scale to sort things out and optimize distances/sizes/etc.

I used this method to make a compact 1-1/2" porting valve a while ago...

Image Link

Didn't use the exact specs, but the dimensions are the same as in the drawing (1 pixel equals 0.01").

A good plan is key.

EDIT: adding to Crowley's post, the plug in the image I linked to sealed fine with the gasket method described (the orange disks are silicone rubber). :wink: A heavy weight is placed on the plug during construction before drilling and tapping the holes for the bolts to hold the plug in. This way, the gasket is compressed when the plug is bolted in.
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Unread postAuthor: Lockednloaded » Sun Mar 21, 2010 11:15 pm

The only thing i'm having a real problem w/ is the front part w/ a threaded adaptor. As for the back plug, i might just manage an o-ring seal w/ my drill, but could you elaborate on this gasket method please I'm really confused :?
a vid tutorial would really help deathbyDWV is it the bcvids one, if so, i have already seen it
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Unread postAuthor: mark.f » Sun Mar 21, 2010 11:29 pm

If you'll look at the drawing, you'll see there are two bushings inside of the front of the tee. Both are cut down to fit into the same socket. One is threaded, the other is not.

EDIT: also, the back of the rear (slip) bushing is sanded down to fit into the interior of the tee to allow more area to bond to the piece of pipe the piston seals against. You may or may not have to do this for your valve.

EDIT II: Here's a link to an old thread I made while compacting a1-1/2" porting piston valve. Notice it doesn't use the newer design.
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Unread postAuthor: iknowmy3tables » Mon Mar 22, 2010 3:49 pm

might I propose a diaphragm design as a possibility
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Unread postAuthor: deathbyDWV » Mon Mar 22, 2010 6:05 pm

a vid tutorial would really help deathbyDWV is it the bcvids one, if so, i have already seen it

Yep... That was it...[/quote]
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Unread postAuthor: Lockednloaded » Mon Mar 22, 2010 6:31 pm

might I propose a diaphragm design as a possibility

not too familiar with diaphragm valves myself, but i do know that they are know for their amazing opening speeds and compactness. The only experience i have with diaphragms is my SV semi, which I am currently changing into an inline piston valve.
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Unread postAuthor: iknowmy3tables » Mon Mar 22, 2010 6:35 pm

hey I think you were asking about how mark's valve seals the plug well here's the how-to he wrote
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Unread postAuthor: mark.f » Mon Mar 22, 2010 7:42 pm

Thank you ikm3t. I must have misread something. :oops:
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Unread postAuthor: Lockednloaded » Thu Mar 25, 2010 9:51 pm

Thank you for your help, This weekend i will head to homedepot to purchase the parts, i will probably just go with an o-ring seal on the back plug, but i'll but a few for experimentation. Completion may be delayed abit because I am building an airsoft shotgun with my semi-auto system for a friend of mine.
Back to the valve, i will most likely use a cast hotglue piston, i will not add a peice of pipe in the tee as mark.f did, instead i shall have the barrel go much further back. I beleive this will eliminate most of the excess pilot volume almos to the point where i can pilot with a blowgun
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Unread postAuthor: mark.f » Sun Mar 28, 2010 11:36 pm

Well, the pilot volume is really quite small. Your piston still needs to come back at least 1/4 of the diameter of the port, plus room for a bumper.
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Unread postAuthor: Technician1002 » Sun Mar 28, 2010 11:45 pm

1/4 the diameter applies where the air can enter the gap from all sides. In a T up to 2/3rds of the path is blocked by the body of the T. A larger opening will be required to keep the performance up.

It works well for coaxial designs. Even then I try to have the piston open at least 1/2 the piston valve seat diameter. I like the entrace to the barrel be the only notable restriction without a series second restriction of a small piston to valve seat gap.
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