help me design a pulse valve for a pneumag

[rawbutter]

I had a brainchild while showering the other day. After building a bunch of pneumags, the problem I always run into while trying to shoot fast is that finger-off-the trigger moment. I can walk decently fast, but inevitably I short stroke because I take two shots that are too close together. This usually results in a misfire, or a low FPS ball that gets stuck in the barrel and then shot in the back by the next ball, causing a barrel break.

It dawned on me then that the real problem is the on/off valve itself in the pneumag. When I'm holding down the trigger, the valve is on, providing constant pressure on the sear. When I let go, the valve releases pressure and allows the sear to reset. But if I press the trigger again too quickly, the pneumatics don't have time to vent properly (at least I'm assuming it's the pneumatics and not the Automag on/off, which recharges stupid fast).

So what if the valve itself was different? What if it provided a pulse of air instead of a constant stream?

This is the way a typical MSV on/off valve works inside a pneumag (at least to my limited understanding).



Air goes in one port, and when the pin is depressed, air is allowed to move through at constant pressure.

But what if the o-rings were moved into different places? Something like this?



In this configuration, only the air trapped between the two o-rings would move forward.

The main problem I see with this is that the sheer volume of air going into the piston would be minuscule, and it might not have enough power to actually move the piston at all. So the valve would either have to be larger or operate at much higher pressures. But I'm sure there are other problems too that I'm not seeing.

Any thoughts?

[Patron God of Pirates]

Okay, I'll bite. Advise that I'm no kind of air smith. It seems like the minuscule air problem could be solved by incorporating some kind of dump chamber into the valve.

The below drawing has obvious problems, but you get the idea.

[athomas]

You just can't move a closed chamber of air around. Remember the gas law. P1V1 = P2V2. The chamber volume (V1) is a fixed size and contains air at the regulated pressure (P1). If you move that chamber of air so that it connects to a piston chamber to move a piston, then the volume of the occupied air space increases. So the new volume (V2) is significantly larger than the old volume. Therefore, the new pressure (P2)will be significantly less. Less pressure would result in less force being applied. The only way to successfully move a piston without reducing the force as it moves away, is to maintain input pressure through its full motion. That requires opening a direct passage from the input to the piston.

[nak81783]

I'm probably not offering anything new here:

Short stroking has always been an issue with Autocockers and Automags. They don't have mechanical disconnects like blowbacks or firearms. The problem with disconnects is they typically increase trigger pull force, length, or both. Electronics were the solution to this. So somewhat similar to your pulse idea, if you could figure out a mechanical or pneumatic means of letting the firing and resetting sequence occur once INITIATED by the trigger, but not dependent on the trigger's full travel, that's your solution. But as stated, electronics were the simple way to do this.

[bowcycle]

... or just shoot the MV, T-Rex and Ultra Blade trigger.

I didn't know if you were just choosing not to brag, but aren't the OP's concerns the reason you designed the t-rex?
well, that and simplicity's sake.

[rawbutter]

You just can't move a closed chamber of air around. Remember the gas law. P1V1 = P2V2. The chamber volume (V1) is a fixed size and contains air at the regulated pressure (P1).

Damn. That's a good point. I forgot about that. So even if there was a dump chamber the same size as the piston, the pressure would drop by half (at least) when that air is released. Hmm....doesn't sound very efficient.

And yes, I do admit that Luke's T-Rex mostly solves this problem. I did get to shoot one recently, and the short stroking was non-existent. Still, it's a fun thought experiment.

[Spider-TW]

Given Luke's refinements and various electronic solutions, let's set aside practicality for the moment.

Pneumags are not the only marker to want a pulse valve. Have you seen this thread?

http://www.mcarterbrown.com/forums/c...able-mech.html

which goes back to another;

http://www.mcarterbrown.com/forums/c...res-sorry.html

None proven that I know of (lmk if you find one). They obviously need some precision machining. The same reasoning of valve recharge time is where my analog control came from, which works with no other considerations or programming, so I expect the idea of a pulse valve is viable.

There are two things you are after, a latching dump valve (not too bad), and a repeatable time delay (hard). The time delay is relative to your pressure, volume and flow rate. The above attempts have calculations behind them, but are fixed designs. If I were going to play with the design, I would get some medical grade needle valves and make a bench setup. There's a company for those valves, starts with a B. (Beswick!) I would try to make the volume adjustable in some fashion. You are kind of stuck with the pressure (~80 psi?). Once you get that functioning, step back and see how to integrate it and make it cheaper. Or, just stuff it all in a custom wood stock and play with it.

[Nobody]

op?

Op = Original Poster

[jade_monkey07]

Caution. Long post TLDR: I want to modify the pnuemags to have anti short stroke with a selectively placed hole, similar to the level 10.

I had a brainchild while showering

Any thoughts?

I had no idea this post existed and I approached Luke the other day with a theory. My brain went the same direction as you at first, but I couldnt think of a viable solution.

This is what I sent him.
"Hey Luke. I was just brain storming an idea and wanted to run it by you. This may be something you've already thought of. Or maybe the oltr works differently than the rest.
But First a question. How does the oltr reset it's piston/plunger, is it solely the sear pushing it back into place?
The reason I ask is I've always loved the idea of pnuemags, I owned 2 gforce frames a cheater and made my own with a kit. But I can never get over my fingers short stroking when I try to walk it.
I was trying to think of a way to shut off the gas while the bolt is in motion but nothing made sense. Then it hit me.
What about to having something like the level 10 built into the oltr to prevent the short stroking.
Have a small hole in the chamber of the oltr near the pistons most forward position/the valve firing point. Where pulling the trigger again before the sear resets the piston past the hole, just vents air without enough strength to interfere with the sears motion. I think if you got it in the right spot it could work. I'd love to hear your thoughts. I could come up with some drawings if you'd like.

Hankering to tinker
Mike."

He kindly asked me if I had tried his oltr with MV and I have not. It may be tuned to perfection. But this is strictly a "I want to know if this will work"
It could possibly be used on any pnuemag

Now I'm not a numbers guy, but I can envision things and trail and error the crap out of stuff. So I think there is potential here.

Theory is to get the hole in the correct spot so there is still enough momentum in the piston to activate the the sear.
But far enough back and big enough hole that even if the trigger is held the return action of the sear can get to the point of the valve resetting.
This would make it so even if you pulled it again part way the air would hopefully just vent. An rt on/off with its greater return than pull force will most likely be necessary


things we would need to know.
1: At what point to put this hole in the oltrs/cheater piston travel.
2: what size the hole needs to be.
3: what relation would the psi from the lpr have on these other two points?

Brain storm ideas at this point. Maybe a heavier piston would be required to carry some momentum?

How to trial and error this?

Instead of a hole that will be difficult to place and size I thought about taking a triangle file and starting a notch in the bottom of the chamber. Shallow and short at first.
To rule out lpr, lower the pressure all the way. Air up marker, raise lpr pressure till it shoots. hold the trigger and See if it can reset on its own. Disassemble,
one light pass of the file, making it longer into the chamber and deeper
Rinse and repeat Till something happens.
Either it works or it stops working forever lol. Nothing a little jb weld won't fix though

One thing I think that could come up is a constant rt bounce if the "trench" isn't letting enough air out.

I wish I still had my cheater. I'd gladly tear into it to try out.

Any thoughts?

I can come up with some drawings if anyone is unclear on this






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[Chris TS-1438]

You should go back to the kingdom of excessively long posts
And stay there... please.

[jade_monkey07]

I didn't think this was YouTube where people have the attention span of goldfish. Added a TLDR (too long didn't read) to the top of the post.

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[Chris TS-1438]

Substance keeps attention. Not length.

[jade_monkey07]

If you've got nothing good to say why say anything at all? Post whoring? Troll? Do I need to answer a riddle to pass?
Constructive criticism on the topic at hand please

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[Chris TS-1438]

Your post seems like satire. One post in this thread mentions
Boyles law, and others are explaining valve function. Your post is way longer and explains
How you "aren't a numbers guy," and want to file the inside of a valve to improve it (or ruin it) through
Trial and error.
I am amused. The grass must be extra sticky in Calgary. Have some poutine for me.

[jade_monkey07]

Go ahead and show me the math then? Didn't think so

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[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.



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



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....



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.)