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New guy: My primitive pneumatics

Built a pneumatic cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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New guy: My primitive pneumatics

Unread postAuthor: Daltonultra » Mon Nov 24, 2008 10:39 pm

Hey! New guy to the forum, old hand on the combustion side of things.
Last year I tried putting together a pneumatic on the same plans as that John W. Cornwell jerk(tried getting advice from him on modding the valve, he basically told me to go screw), but couldn't get the darn valve to work. So, recently I dug the carcass out from beside the shed and resurrected it with a ball valve. It looks a little strange because of the way it was recycled, but it works. In fact, it works insanely well for such a slow mechanism. Now I'm completely hooked...
I even made another smaller gun with a 1/2" copper barrel.

I wish I had known about this site last year. Now that I know how to mod the valves, I'll be pulling the old Rainbird 2" sprinkler valve back out, and buying a new 3/4" Lawn Genie valve for the smaller one.

Anyways, on to pics and vids...

My Youtube vid of me destroying an old defunct CD changer. The smaller gun uses lead shot, and a metal rod with a wicked point. The larger gun normally fires potatoes, but in the vid I used a broken shovel handle with a knob on the end that neatly fit into the 2" barrel.

BTW, be kind, I'm new to video editing, too. :lol:

http://www.youtube.com/watch?v=5NfLklSD8NU

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Last edited by Daltonultra on Wed Dec 03, 2008 5:42 pm, edited 1 time in total.
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Unread postAuthor: hi » Tue Nov 25, 2008 12:04 am

hate to be the one to point it out, but you have a DWV reducer on it. looks tile the wye and elbow are too. DWV isnt considered safe to use with pressure. just to be on the safe side either change it or keep the pressure below 50 psi or so. people tend to make a big deal out of it, so i thought i would point it out.

otherwise it looks good and is a good start.
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"physics, gravity, and law enforcement are the only things that prevent me from operating at my full potential" - not sure, but i like the quote

you know you are not an engineer if you have to remind yourself "left loosy righty tighty"
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Unread postAuthor: Daltonultra » Tue Nov 25, 2008 12:12 am

Where can I get PVC pressure fittings?

BTW, it's been to 150psi(with me on the other side of a wall while it filled), and had no problems. My max for shooting is 120psi.
I'm planning on some re-engineering for the big one, sprinkler valve, more volume, etc...I guess I can throw better fitting on that list.
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Unread postAuthor: starman » Tue Nov 25, 2008 12:31 am

You have your small bore gun in a pinch situation between at the chamber/copper elbow joint with the chamber taped up to the barrel in and angle like that. It may survive but it isn't ideal. Build a spacer brace to insert between the barrel and chamber and return them to a parallel position.

On your big gun, instead of the bell reducer, use a coupler/reducing bushing combo. Keep your max psi at 120 and you should be OK.

Welcome to Spudfiles!
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Unread postAuthor: MrCrowley » Tue Nov 25, 2008 12:49 am

Hey nice cannons dude. Pity about the DWV, good thing is it gives you an excuse to build another one ;)

I wouldn't push 70PSI with it, i've had pressure pipe blow up on me before and you're in a colder environment.

PVC and cold (below 0 degrees celsius), is also very dangerous. PVC becomes brittle when cold and it's pressure rating and structural integrity rapidly drops.

Best to keep to metal when out in the cold.

This article will tell you how to identify DWV and pressure pipe, hope it helps:
http://www.spudfiles.com/spud_wiki/inde ... _Rated_PVC
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Unread postAuthor: Daltonultra » Tue Nov 25, 2008 1:08 am

Well, when I redo the big one, the tank will basically be redone as an "U" shaped piece with a T coming up off one end with a 2"reducer(I'll use a bushing there) and a threaded 2" coupler to the sprinkler valve.

I've got a chunk of Delren plastic downstairs I plan on using for a piston. Just have to find someone with a metal lathe to machine it down for me.

The small gun actually isn't pinched or bent in anyway. The machining in the elbow threads is crooked, so the entire top assembly naturally rests that way even without the duct tape on it.

EDIT: I'm gonna head over to Worly plumbing tomorrow and see what I can dig up.
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Unread postAuthor: starman » Tue Nov 25, 2008 3:36 am

Daltonultra wrote:The machining in the elbow threads is crooked, so the entire top assembly naturally rests that way even without the duct tape on it.


...Uhh crooked...?? And you didn't use a standard threaded PVC bushing to connect the copper...you milled and tapped your own crooked bushing?? Sounds like a whole lot of trouble just to avoid a barrel/chamber spacer....
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Unread postAuthor: Daltonultra » Tue Nov 25, 2008 9:18 am

starman wrote:
Daltonultra wrote:The machining in the elbow threads is crooked, so the entire top assembly naturally rests that way even without the duct tape on it.


...Uhh crooked...?? And you didn't use a standard threaded PVC bushing to connect the copper...you milled and tapped your own crooked bushing?? Sounds like a whole lot of trouble just to avoid a barrel/chamber spacer....


Crooked, as in, the threads on the brass elbow were machined at a slightly acute angle, so that the PVC tank and copper barrel naturally sit about 1/16th of an inch apart. Don't ask me how it happened, I'm not a machinist. In fact, when I realized what happened, I was kind of annoyed. But once I sweated the barrel in and threaded it into the valve, it turned out that everything fit perfectly.

The PVC bushing is from Lowes, unaltered, and is a 2" male socket weld to 1/2" female threaded.
In fact, everything on that gun is from Lowes, with no cutting or machining done by me at all. They sell PVC in 2' lengths, and copper in 5'. All I did was assemble the pieces.
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Unread postAuthor: starman » Tue Nov 25, 2008 9:23 am

Cool then, looks like you got a defective part and made it work to your advantage. That's quite an ugly angle on there...under most plumbing circumstances could not be tolerated.
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Unread postAuthor: Daltonultra » Tue Nov 25, 2008 9:28 am

BTW, on the big cannon, you guys are right, the elbow, and "Y" are DWV. I'll correct that oversight when I rebuild it. The rest of the fittings were bought at Worlys, when I built the original form of this cannon, and are NSF-PW, including the reducer.It's been a long time since I built the original gun, and I forgot to check the new fittings when I rebuilt it for the ball valve.
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Unread postAuthor: Daltonultra » Tue Nov 25, 2008 9:30 am

starman wrote:Cool then, looks like you got a defective part and made it work to your advantage. That's quite an ugly angle on there...under most plumbing circumstances could not be tolerated.

Yeah. If I found that angle in my house plumbing, I'd probably be POed...
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Unread postAuthor: jrrdw » Tue Nov 25, 2008 12:06 pm

Nice job on the cannon.

Use the edit button if you have more to add and it's the last post (meaning no one has posted after you).
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