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No more piston slap!!... maybe...

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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No more piston slap!!... maybe...

Unread postAuthor: ThornsofTime » Fri Oct 15, 2010 4:49 am

Ok... so I work nights at a hotel and have nothing better to do than sit around and design.

This gun,
http://www.spudfiles.com/forums/paca-mk ... 21703.html
inspired me to want to make a launcher with a similar QDV (I BELIEVE his valve would be a QDV... correct me if im wrong) build into a Tee fitting.

HOWEVER- as I typically share my creations with my friends (and some of them are MORONS), that trigger would end up hurting someone.

Heres a little redesign that I think might solve the problem. It separates the trigger and piston, but requires that the trigger be mounted in a wood frame with the piston access just above it.

Question- would this valve be safe @500psi?? or would the piston smash back too hard and rupture the back tube (the one with the spring in it)??

EDIT- Second question- what type of copper tubing should I be using for a pressure chamber?? (I have the copper handbook... but that crap confuses the hell outa me). Im looking for 300-400psi in a 12" long 3/4"diameter pressure chamber.
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Unread postAuthor: Crna Legija » Fri Oct 15, 2010 6:16 am

Is that spring pulling the piston back? if not it wont work. all i see this doing over a normal barrel sealing piston valve is making it more complex and making the piston heavier.
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Unread postAuthor: ilovefire » Fri Oct 15, 2010 6:33 am

i would also have to say that at 500psi i think that trigger would get really hard to pull back
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Unread postAuthor: ThornsofTime » Fri Oct 15, 2010 6:38 am

Spring is is pushing bolt forward, sealing the valve.

trigger pushes BACK on the spring, unsealing the barrel just enough to let air pressure slam the piston back

once air pressure drops (aka the launcher fires) the spring returns the bolt to the forward position, again sealing the valve.

I think your reading "complex" because of the third head on the piston. This head really serves 2 purposes: something for the trigger to snag, and helps keep the piston centered as the first head comes out/goes into the barrel. The o-rings on the third head seem to allude to a seal of some kind but thats not the case.

The whole design is almost exactly the same as the one on the previously linked launcher. however, I replace his nuts and coper trigger with a third head thats nudged by a trigger. This solves the problem he had of his trigger slamming back once he fired the launcher and allows you to relocate the trigger almost anywhere behind the Tee fitting.
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Unread postAuthor: Crna Legija » Fri Oct 15, 2010 6:49 am

i recon its complex because a barrel sealer would be slightly more powerful(lighter piston) and much easier to make. It would probbly be smaller as well
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Unread postAuthor: ThornsofTime » Fri Oct 15, 2010 7:41 am

O_o how does a barrel sealer work... info or link pls. Basically im interested in any possible way to build a valve using a Tee fitting as the body.

(sorry... im still TOTALLY a pneumatic noob.)

@ilovefire- yeah probably. I would just like it to HANDLE 500psi, so that I would feel comfortable operating it at ~350psi. My plans for my next build call for a larger bore and higher psi. Probably common knowledge to everyone here... but I wouldn't have known that that would make the trigger pull harder :oops:
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Unread postAuthor: Technician1002 » Fri Oct 15, 2010 10:17 am

With pipes screwed into a T the pressure will remove the o rings when fired. I'm working on a variation where a t has the threads ground out so a pipe nipple can slide inside the T, regular QDV ports cut, and welded in place inside the T. You will need a robust energy absorbing bumper.

From there a pipe cap can be used on the breech and a coupler can be used to join the barrel.

@Thornsoftime.. http://www.spudfiles.com/spud_wiki/index.php?title=Piston_valve
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Unread postAuthor: Gippeto » Fri Oct 15, 2010 6:28 pm

Type M 3/4" drawn copper has a rated internal working pressure of 701psi @100F...pg 26.

Sweated with 95/5 tin/antimony, the joints are rated for 1090psi @100F...pg 28

Actual (theoretical) burst pressure of 3/4" type M...4715psi...pg 29.
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Unread postAuthor: ThornsofTime » Sat Oct 16, 2010 12:40 pm

@Gippeto- Tanks for the info :) Ill need to see what kind of solder I can find at home depot. I have a BUNCH of silver solder round the house in hard medium and soft (for jewelry applications) but I have no idea as to its pressure holding capabilities. Is that 95/5solder a common mixture available at Home Depot?? or is it something im gonna have to smelt?
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Unread postAuthor: Technician1002 » Sat Oct 16, 2010 12:50 pm

The hard and medium will work well. The brazing temperature required for the hard solder will aneal hard drawn copper as well as promote oxidization.

Flow Dry Nitrogen in the pipe before high temperature silver brazing is attempted to prevent copper scale.

This video clearly shows why.
[youtube]http://www.youtube.com/watch?v=3uP-eb8Zz08[/youtube]
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Unread postAuthor: ThornsofTime » Sat Oct 16, 2010 2:41 pm

For the purposes of a spud launcher, Nitro presence is almost excessive lol. It defiantly has its uses (mostly in closed pipe systems where you will not have access to clean the internal areas of a pipe) in home manufacture and other plumbing situations where the oxidized flakes would run thru a system and wreak havoc on other parts.

Oxidization itself really (structurally speaking) does little to effect any change in copper. When it DOES oxidize it literally only affects 1/1000th of a millimeter of the thickness of the metal, where as steel oxidizes at a much more violent/progressive rate. The major factor to watch out for while soldering is annealing, as this is a change on a molecular level, rearranging the molecules spreading them out and forming a structure that changes its overall "toughness".

@Technician1002 good/useful information, but as I dont have all the necessarily equipment to run a nitro line, I just might have to stick to regular sweat soldering &or just go to galvanized steel pipe and fittings.
Those nitro setups tend to be quite expensive and all im working with is this.

http://www.toolfetch.com/soldering-braz ... 50kc.shtml
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Unread postAuthor: Technician1002 » Sat Oct 16, 2010 3:12 pm

CO2 is a cheap substitute. A few chunks of dry ice chucked into the pipe will displace the air as it sublimates during brazing. Do not heat the portion of the pipe with the dry ice. You want some left when you are done brazing to protect it until it cools.
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Unread postAuthor: Big-E » Sat Oct 16, 2010 6:43 pm

Technician1002 wrote:CO2 is a cheap substitute. A few chunks of dry ice chucked into the pipe will displace the air as it sublimates during brazing. Do not heat the portion of the pipe with the dry ice. You want some left wen you are done brazing to protect it until it cools.


This works for mig welding, though. I know a lot of people in my neck of the woods who run CO2 through their welders rather than argon, they claim it works just as well if not better, plus the fact that it's cheaper to fill your cylinders.
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Unread postAuthor: Gippeto » Sat Oct 16, 2010 9:42 pm

If it were me, I'd stay away from the silver solder when dealing with copper and high pressure. As tech mentioned, the required temps will anneal the drawn copper, lowering it's safe working pressure.

There's simply no reason that I can see to use the stuff for room temp service.

The 95/5 is off the shelf stuff at the nearest Home Depot.

I have that oxy/map setup too..(It will do brazing)..I only find it necessary on 1 1/4" copper/brass/bronze. A regular map torch works great for sweating anything smaller. Really hate how long (NOT) those o2 bottles last. :evil:

For interests sake, we run a mix of co2 and argon in the mig at work, it's called "Blue Shield".
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Unread postAuthor: Technician1002 » Sat Oct 16, 2010 11:11 pm

If you do a lot of brazing or welding, ditch the oxy/map oxygen cylinder and get a welding refillable tank with regulator. In the long run it's worth every penny. I do enough torch cutting to use plenty of Oxygen so I bought a tank and have it refilled. Due to the high pressure, they last a lot longer than the low pressure disposable tanks. I have an 80 CuFt tank. The disposable ones are about 1 cubic foot.

Reference;
http://www.castlewholesalers.com/BERNZOMATIC-OX9-1-1-cu-ft-Disposable-Oxygen-Cylinder.html

About the smallest refillable tank you can get for the small torch is 10X that amount.
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