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3 way 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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3 way valve

Unread postAuthor: Lentamentalisk » Sat Feb 23, 2008 3:14 am

Have any of you seen a 3 way valve for cheap anywhere?
The general idea is to have a 3 way valve that is button triggered, that has one port open at stasis, and then when you press the button (or trigger or what ever) that port closes and the other opens.
I was thinking of using this with a QEV cannon to have it hooked up to a huge air supply through the open port, and then pilot it out through the normally closed port. This would hopefully make an auto-refilling QEV cannon, so I only have to worry about reloading ammo.

If you have any leads as to where to find one, I would greatly appreciate if you told me. I have checked McMasters somewhat throughly, but its possible that I missed something.
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Unread postAuthor: PinHead » Sat Feb 23, 2008 10:43 am

I've been looking for one for some time too, but I've finally given up and decided to make my own. I figure I can build it cheaper than a boughten one, anyway. When I get the drawing finished I'll post it here.
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Unread postAuthor: PinHead » Sat Feb 23, 2008 10:55 am

Ok, here it is. Sorry about the double post.

What I didn't show here is that there will be steel nuts welded over the ports drilled in the tubing. These nuts should accept a standard NPT fitting; I assume that they make nuts with the correct pitch to do so.

The port on the left is the exhaust port, the port on the right is to your constant air source, and the port in the center goes to your chamber to fill. When the rod is moved side to side, each of the outside ports are allowed access to the center port. As shown, it is set in the middle; about halfway thru the trigger pull.

You won't need a QEV for this design, as it will exhaust on it's own from the trigger stroke.

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Unread postAuthor: psycix » Sat Feb 23, 2008 11:57 am

I like the 3-way design PinHead.
Do the 1/2" washers seal off well enough?
Arent pistons with o-rings required?
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Unread postAuthor: PinHead » Sat Feb 23, 2008 2:40 pm

I haven't tried it yet, but I'm hoping that the washers will be sufficient if I don't go too high with the pressure. The nice thing about the washers being sanwiched between two nuts is that when tightened, they will expand a bit, which should help things seal up nicely. The washers will also help stiffen them up enough to keep their shape; with a 3/8" washer in a 1/2" bore, there will be only 1/16" on each side sticking out. I would hope this would offer the same ability as an o-ring. Plenty of air-tool lube would help keep it sealed as well.

The only drawback is that the trigger stroke would have to be twice as long as the size of the port; in this case, the trigger pull would be around 3/8" of an inch. Larger ports would offer better performance, but then again, your trigger pull increases proportionately.
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Unread postAuthor: Lentamentalisk » Sat Feb 23, 2008 3:48 pm

Ingenious design I must admit. The problem I see is the whole device needing to be rather huge... It would get in the way of your hand holding onto the handle it seems, assuming you were using it like a standard trigger on a gnu (are we allowed to say the g|u|n word? I dont remember lol)
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Unread postAuthor: PinHead » Sat Feb 23, 2008 4:42 pm

The problem I see is the whole device needing to be rather huge...


Not necessarily... keeping in mind that the bore of the tube is only 1/2", it would be a fairly small piece, only about 4 inches long or so, maybe even a bit shorter. And I planned on having a handle or grip built into it later, which wouldn't take much.

To depress the rod to actuate the device, I planned on using the trigger from a cheap plastic spray bottle. Look at this page for an animation.

http://science.howstuffworks.com/question673.htm

You'll notice that it has a plunger with a return spring built into it. So basically, all you'd have to do is cut everything else off but leave the hinge trigger, spring, and plunger intact, and then connect the rod from the 3-way to the plunger.
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Unread postAuthor: clide » Sat Feb 23, 2008 4:45 pm

Here is a small push button 3 way valve, you'll have to deal with 10-32 threads, but it should work.
http://www.mcmaster.com/nav/enter.asp?partnum=62475K11

You can also search for directional control valves to all kinds of different 3-way valves.
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Unread postAuthor: Lentamentalisk » Sat Feb 23, 2008 6:40 pm

@clide: It says its a 3 way, but that it only has 2 ports, does that mean that one vents to the atmosphere or what?
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Unread postAuthor: clide » Sun Feb 24, 2008 1:21 am

Lentamentalisk wrote:@clide: It says its a 3 way, but that it only has 2 ports, does that mean that one vents to the atmosphere or what?


yep
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