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My Second Generation Piston Valve cannon

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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Unread postAuthor: clemsonguy1125 » Sat May 08, 2010 10:23 pm

I'm all for testing the failure, are you going to hydo test
it or what?
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That is all.
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Unread postAuthor: Mr.Gadget » Sat May 08, 2010 10:39 pm

Thanks for the spring info, Yes I have thought of that as a solution,, and an easy, cheap one at that. But not a real concern, just a simple reset on start up.

Ok, I only shoot at people that are informed, PROTECTED, and willing participants, and shooting BACK at me. So I would consider that to be in the catagory of paintball/airsoft/scenario play.

All of you are really cool people, with even more stuff I can learn. Remember, this is only my second pneumatic piston cannon.

Lets take a short vote,,,,,,,,, Who wants me to SAFELY CAUSE A FAILURE on a soda bottle. I will be safe, with video, and guages and all the cool stuff. I'll do it, for other peoples benifit ...........SAFELY!!!!!

Oh one last thing,,,,, I will try not to be so long winded from now on. (thanks for that input)
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Unread postAuthor: Mr.Gadget » Sat May 08, 2010 10:48 pm

Well Yes Colonel clemsonguy1125,
It is a sprinkler valve. It turns out that the $11 dollar valve does a better job than the $15 valve. I could have taken a beter picture, but i figured if the looker knew what it was, they at least knew how it worked.
With the $11 valve, there is way less Humm/moan and more POP from the muzzel, I like it!!!!! I used the 1" version.
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Unread postAuthor: Mr.Gadget » Sat May 08, 2010 10:53 pm

Colonel,

I will not Hydro test... I want to see a Pneumatic failure, on a pnematic cannon. With all the glory of a high humidity, 90+ degree enviroment I now live in.

Thats a +1 for the induced failure!!!!! :D
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Unread postAuthor: maverik94 » Sat May 08, 2010 11:28 pm

I agree. Lets see a safe test and see at what pressure one of those bottles will blow! Make sure to start a new thread for that though! But in the future, please don't double post, use the 'edit' function on the upper-right hand corner of your post if you need to make changes to you post. you just made a triple post.. :cry:
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Unread postAuthor: Mr.Gadget » Sat May 08, 2010 11:37 pm

Sorry about the double and tripple post, My bad,,,,, I am the new guy.
And to be sure, I will start a new post for the PET soda bottle failure.

Safety Failure,,,, That just sounds like so much fun!!!!!! :D
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Unread postAuthor: Lockednloaded » Sat May 08, 2010 11:41 pm

Mr. Gadget, that's a very neat little toy you got there! I bet it suits it's paintball purposes well, but might I reccomend a destructive cannon for your next build; you won't be dissapointed.
And welcome to spudfiles! I can appreciate your good grammar, but even on a "formal site" like ours, things like including rank and long winded paragraphs can be frowned upon some times. After all this is still tEh IntErnetz not tea time with the queen! :lol:

^God I'm such a hippocrit look how long that was... ^
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Unread postAuthor: Insomniac » Sun May 09, 2010 1:17 am

Interesting use of safeties. As good as a mechanical safety is, it is still not entirely foolproof. A busted hose or any other kind of leak can dump the pilot volume and trigger it, though you'd have to be pretty unlucky to have that happen. If you want an utterly foolproof safety, you can't go past a ballvalve right before the barrel. If it's closed, the gun won't fire, period.

And to the people discussing the safety of the chamber, 40 psi is well within what a soda bottle can hold. At a friend's house we fired arrows at some soda bottles (they ranged from 1.25 to 2 liter capacities), after pressurizing them to ~150psi with an air compressor. Two bottles failed spectacularly, but one managed to just sit there and leak, with a small hole where the tip of the arrow had cut through. At 40 PSI I think it's extremely unlikely that the venting pressure would be enough to produce a dangerous explosion. Rather, it's much more likely to just leak out.

Though some testing on the matter would be quite interesting indeed...
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I wonder how much deeper the ocean would be without sponges.
Right now I'm having amnesia and deja vu at the same time. I think I've forgotten this before.

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Unread postAuthor: Gun Freak » Sun May 09, 2010 8:29 am

Lockednloaded wrote:And welcome to spudfiles! I can appreciate your good grammar, but even on a "formal site" like ours, things like including rank and long winded paragraphs can be frowned upon some times. After all this is still tEh IntErnetz not tea time with the queen! :lol:


Tell that to Rag :D
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Unread postAuthor: mark.f » Sun May 09, 2010 10:30 am

For what it's worth, Plasticex009 did a hydrotest on a standard 2-liter bottle before, using a water-filled bottle and dish soap pumped through a grease gun.

*Rummages through archive.org's Wayback Machine*

Loooong link

He found they distorted at around 120 PSI, but I suspect the construction varies from manufacturer to manufacturer...

Click on the images on the page to see them, as the thumbnails don't load.
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Unread postAuthor: Technician1002 » Sun May 09, 2010 11:09 am

As long as we are on the discussion of the merits of a soda bottle as a pressure chamber, the soda bottles were one of the reasons I tested ABS. The logic is the 2 non core walls of the pipe are each thicker than a pop bottle, of similar pliability, and therefore might be able to safely hold the same or greater pressure of a soda bottle. The failure mode of pop bottles are fairly well known from all the you tube (not safe here.. example is for material discussion) works bombs and Dry Ice bombs.
Please do not discuss making or using these items here, it will get the thread locked.

Knowing that PVC is not approved for compressed air service due to it's failure mode and ABS DWV is not approved for pressure, I knew that I would have to test ABS on my own. That in a nutshell is the reason the ABS Cellular Core cannon was built. The results have been fantastic. If you build with ABS, remember, it is not rated for pressure. If you build with PVC, remember it is it not rated for compressed air.

Some day unless someone beats me to it, I'm going to use a grease gun, water, and pressure test a piece of 4 inch ABS Cellular Core DWV pipe. From what I have seen so far, I'm thinking it has a higher burst pressure than a 2L pop bottle.
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Unread postAuthor: Mr.Gadget » Sun May 09, 2010 11:11 am

Insomniac,
While that would be a very unlucky situation, a ball vavle used as a safety seal, not burst control is a tempting idea. Thanks for that input. Is this something you have done yourself, or seen done before?
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Unread postAuthor: Insomniac » Mon May 10, 2010 12:54 am

I've never used it myself (I only briefly owned a small ballvalve cannon, never made anything nice because of the issues with legality here in Aus), but I've seen it on a few cannons. It is of course more practical with small bore launchers (as you can get a valve the size of the barrel so as to not constrict flow) , but it should still work fine on yours provided you use a large enough valve (PVC ones will be fine for the pressures your using and shouldn't be too expensive). It's the most effective safety you're ever going to find, and I'd certainly trust it a lot more than a mechanical one on the trigger.
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I wonder how much deeper the ocean would be without sponges.
Right now I'm having amnesia and deja vu at the same time. I think I've forgotten this before.

Add me on msn!!! insomniac-55@hotmail.com
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Unread postAuthor: saefroch » Mon May 10, 2010 10:15 am

2 liter soda bottles rupture at about 180 psi. Usually when they rupture they either tear up one side or fragment the top. Either produces significant shrapnel, but the air resistance to inertia ratio is so massive that shrapnel never travels far. - All from personal experience.

Love the safety additions on your gun, I'll have to add one to my recently finished (sort of) piston valve rifle thingy, because with the rear seal on the piston a small bump on the pilot valve leaks enough air to trigger the pilot... not totally safe if you're not watching where you're swinging a 4'8" steel cannon holding 200+ psi. I love the dedication to safety, if you hold to that you could create some pretty designs that are actually safe and comfortable to carry around, without fear of bumping something and setting off a prepped spudgun. Rock on.

(If you haven't noticed I tend to get wordy... here I go again)
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Unread postAuthor: Mr.Gadget » Thu May 13, 2010 8:32 pm

By Request,
Here are some close ups of the internals.
For the bumper, I went to the dollar store, and bought a set of flip-flops. I shaped it with a dremal tool, and used JB quick to attach it. 200+ shots zero failure.
The felt on the piston, allows it to slide, no lube, and provides a minor seal to actuate it back to the forward possition. Don't judge,,,, it works. 200+ shots with zero failures.
Everyone have fun, and keep it safe. Think about it before you do it.
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Attachments
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