help me design a pulse valve for a pneumag

[rawbutter]

I've had the same idea about the hole in the piston, Jade. And I don't think the hole would need to be as precise as you think. If you pull the trigger on a normal automag, you'll notice that the marker fires before the trigger bottoms out. So there's some play there. As long as the piston o-ring hits the hole after the marker fires, it should vent the air inside (or at least most of the air inside so the sear can reset).

The bigger issue is stopping the air coming into the piston. You want the air to be delivered as a pulse, so when it vents out the hole, there's no air left inside the piston (or very little) to stop the sear from resetting. Pneumag designs don't do this, though. The air is either on, or it's off. And when it's on, it won't matter if there's a vent. It would be like a pinhole in the side of a bucket trying to drain while you're filling the bucket from a hose at the same time. If you made the vent hole bigger than the air inlet hole, then maybe it could work. But that would be a pretty big hole (larger than 1/8" probably). At that point, it's possible that the escaping air could eventually deform the o-ring that's passing back and forth over the hole.

So yeah, the vent hole is a step in the right direction, but I think it needs to work in tandem with a pulse of air.

(I thought your long post was fine, but the way. This is a pretty complicated idea. It's not going to be solved with short posts.)

[Chris TS-1438]

If your vent hole was small enough you might be able to create a Venturi effect. I was thinking about that
In comparison to Boyles law. You aren't just containing the pressure like you are when you
Use Boyles law. In this case with constant air pressure your pressure release speed
Would depend on the size of your vent hole, temperature, and with this effect you would see compression to a degree
In the first chamber. It just seems unlikely to stumble upon the right vent size with a file. Probably a more diplomatic way to argue. I'm an ass... keep that in mind.

[jade_monkey07]

I agree rawbutter it would be great to have it as a pulse in tandem with a vent. Two quite complex ideas in their own rights for sure. I will probably be on the look out for a cheater or grab an oltr from luke to do some tests on.
As for the hole wearing out the oring, as long as its deburred and chamfered slightly it shouldn't be an issue.

The only reason I suggested the file idea is because it would be a lot easier to move up in tiny increments in terms of depth into the chamber(placement of the hole) and how deep of a valley it is(size). Definitely crude. But drilling a hole and it's in the wrong spot doesn't leave much room for trial and error. We could obviously make some educated guesses as to where it needs to be. But that doesn't mean it will be correct. Unless I start making my own valves it could be a costly mistake.

I've got some other ideas for a testbed version of the oltr to make the trial and error process less destructive.

To be continued. I've got a photo shoot in the am


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[rawbutter]

I will probably be on the look out for a cheater or grab an oltr from luke to do some tests on.
As for the hole wearing out the oring, as long as its deburred and chamfered slightly it shouldn't be an issue.

There are lots of cheaper parts you can experiment with.

I'm personally planning to use a MAC-43 solenoid valve that I got off eBay for $15. It's small, I already know it will work in a pneumag (because I've used them before), and it's a true five-way valve (instead of most other pneumag valves that are only 2-way or 3-way). For the air cylinder, I'm gonna start with a Clippard SM-6. They also pop up on eBay all the time for $10 or so. At that point, I've only got $25 into the parts, and I don't care much if I accidentally ruin something.

The MAC solenoid works like this.



If I block off the firing port and the left vent, then the valve will fill the idle output when it's at rest. That's where I'll connect a reservoir of some kind. Then when the valve is activated, the idle input will dump into the right vent, which I'll connect to the piston.

It might not work, and even if it does, it will probably only fire once since the air has nowhere to go after it empties into the piston. But that will be a step in the right direction. Then it's a matter of testing a vent of some kind.

[jade_monkey07]

I look forward to see where this takes you. Please keep us up to date even on the failures.

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[dano_____]

You want the Mac valve to fire for a pneumag, just run the input like normal, plug the idle output and plug your cylinder into the firing output. You can now pull the trigger more than one time :)

[rawbutter]

You want the Mac valve to fire for a pneumag, just run the input like normal, plug the idle output and plug your cylinder into the firing output. You can now pull the trigger more than one time :)

Been there, done that. Works great.

[jade_monkey07]

Hey raw butter. In the mac 43 do you remove the electric portion and activate it manually?

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[jade_monkey07]

And can you tap the exhaust ports?

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[rawbutter]

Yes and yes. The exhaust ports are already tapped from factory, and removing the electromagnetic switch is as simple as removing two little screws.

I've actually worked on this idea a little more, but I've run into a weird problem with the fittings. The MAC-43 ports are M3 threaded, and the fittings I have are too big. I mean, they're also threaded M3, but the barb and other parts bump into each other when I'm trying to screw in two right next to each other. So I have to find different, slimmer fittings.

[jade_monkey07]

Take a dremel to them.

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[jade_monkey07]

Anything special happening in that pnuemag your selling right now?

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[rawbutter]

Anything special happening in that pnuemag your selling right now?

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Nope. Just sitting. If it doesn't sell in month, I'm either gonna part it out or double down and cerakote the whole thing burnt bronze and ask for a little more.

[jade_monkey07]

If I didn't already have 90% of a project sitting on my bench in am length I'd jump on it

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[rawbutter]

I finally had the chance this week to make some progress on this idea. I've built a prototype out of Plexiglas, and so far I'm getting some promising results.

pulsevalve.JPG

Here's a close up of how things look when it's resting.

IMG_1600.JPG

At this point, air comes in from the LPR and fills the reservoir. The first o-ring (on the far left of the trigger rod) keeps air from venting out the front, and the last o-ring keeps air from moving up behind the piston. The middle o-ring doesn't really do much here. But....

IMG_1601.JPG

When the trigger rod moves, things change. The first o-ring (on the left) is still keeping air from venting out past the trigger rod. The middle o-ring has moved between the "in" hole and the "reservoir" hole, preventing more air from filling the reservoir. And the last o-ring has moved past the "out" hole behind the piston, pushing it up. (It's not up now because I didn't put air into it for the pictures, but you get the idea.) Last but not least, the vent hole allows all the air inside the reservoir to escape after the reservoir air pushes the piston up. Then a spring behind the trigger rod resets everything.

And it actually works! Sort of. Well, not really. Right now I'm running into two problems.

The first problem is that the trigger rod is hard to push. About as hard as a standard mechanical trigger, I'd say. Definitely not pneumag worthy, and certainly not walkable. Normally, I would ream out the trigger shaft a tiny bit more so the o-rings were rubbing so much, but....

The second problem is that the o-rings aren't getting a good enough seal against the Plexiglas. If I run 20 psi into the pulse valve, everything works. But if I crank it up to 60 or 80 psi (which is the pressure I need to fire a marker), then air leaks past the o-rings, and nothing works.

So I think the next step is to find smaller o-rings. (These are 1/4 inch OD, which is the smallest I could find at my local hardware store.) I might also buy a new bit for drilling the shaft for the trigger rod. (The bits I have are old and perhaps a little bit chipped, which might lead to some irregularities inside the shaft.) Beyond that, though, I'm out of ideas. (I don't want to move to brass yet, since it's very hard to line up all the air shafts without being able to see where I'm going.)