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Large-bore Valve Options

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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Large-bore Valve Options

Unread postAuthor: Zippster » Wed Mar 19, 2008 1:30 pm

Disclaimer: I realize that I've made a thread in the past on the same topic, but with no desire to reanimate a long-dead thread, I've started this.

About a month ago, I dropped a fistful of cash to make my newest toy: a mega howitzer with a 10' long 3" chamber, and a 10' long 2" barrel. This bad boy needed a freakin' ladder to position it, and I couldn't to start knocking satellites out of orbit. But I my rejoicings were premature, as my planned triggered burst disk design failed utterly for complete lack of a seal and a bizarre early burst problem (I'll elaborate upon asking). As you can imagine I was utterly disappointed in the flop, and started brainstorming.

Currently I have a 1.5" ball valve (I know) behind a single burst disk, with the hope that the burst disk would act as a buffer for the slow opening speed of the ball valve (which I had gotten for free from my friend's dad's spare parts bucket). Even this wont work, as the burst disk does nothing but rupture the moment the valve is 1 degree off of closed, or doesn't burst at all and really freak you out. So I now move on.

A few ideas that I came up with are as follows:

- Spring-load the ball valve to increase opening speed
I foresee this not helping much, but it'd be a lot better than it was now

- Double-up on 1" modded sprinklers
The only thing I can envision going wrong is a staggered release of the sprinklers, thus really screwing with the flow etc.

- Just use one 1" modded sprinkler to keep it simple
That's the biggest sprinklers available at the local hardware stores. However this pathetic flow may not do the mega-scale mindset justice.

Please note that I'm not made o money, and am NOT willing to spend any more than $50 if it comes to that.

Seeing as I'm out of time here (class starts in 2 minutes) I'll keep this brief (cough cough):
What are your thoughts and suggestions? Any help is appreciated.

PS:
Don't feel insulted if I don't repsond until Sunday - Im out of town until then.

Thanks,
Zippster
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Unread postAuthor: Sticky_Tape » Wed Mar 19, 2008 1:39 pm

What if you used a piston valve? The piston could be housed in a 3 inch tee and with a 2 inch porting that would work take a while to make though.
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Unread postAuthor: Gippeto » Wed Mar 19, 2008 1:41 pm

Make a piston valve.

Even a 2" tee with 1.5" porting would have higher flow than 2 x 1" sprinklers. (might cost less too)

1.5" = 1.77in2 2 x 1" = 1.57in2

Keep the burst disk if you want to.

A 3" tee with 2" porting would be even better.(of course) :)
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Unread postAuthor: rcman50166 » Wed Mar 19, 2008 3:44 pm

Well if having a quickly reloading cannon was your original idea, then this won't suffice. Just get rid of the valve. The burst disk is only being slowed by the valve. Make the disk tolerate more pressure, then have fun. The positive thing about this is it will save you money, possibly get you money if you sell that valve.
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Unread postAuthor: DYI » Wed Mar 19, 2008 4:26 pm

Fix the TBD valve, or build a piston valve. The piston valve has the advantage of faster reload times, and no extra work making disks. On the other hand, you already have the TBD valve, it just takes a bit of work to make them seal.

What material was the union, what was the disk material, and what kind of gasket did you make to seal it?
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Unread postAuthor: Zippster » Wed Mar 19, 2008 5:26 pm

The problem with the TBD was really, really weird, in that it wasn't just the seal that was acting up, but some freakish fill quirk too. I had it rigged so that the fill valve would fill both the chamber and the pilot, then the pilot fill could be shut off and removed to fill the chamber to the desired pressure. However, the pilot always filled a lot faster than the chamber, which caused problems. Because it filled practically instantly to the regulated pressure, it was always ahead of the sluggishly filling main chamber. Even when the regulator was at 40 PSI and the air seemed to be not flowing, both gauges (one on the chamber and one on the pilot) registered 0. So naturally I'd amp up the regulator, thus causing the pilot gauge to actually read something, then burst and leak the rest of the chamber. Not fun, and utterly demoralizing. I guess the system would work if I fixed the leaks and filled it from a bike pump, but then that wouldnt be very fun either.

Both unions were 1.5" PVC. The gaskets were one 1/4" thick (educated guess) rubber ring on one side, and about 3 similar bike inner tube rings on the other (placement of the rings didnt seem to affect the leaking much). All the rings filled took up the entire space available to them, ie. a doughnut with a 1.5" hole in the middle. The burst disks were 3-5 ish layers of aluminum foil, same size as the gaskets just w/o the hole. I tightened up both unions 2-person hand tight (thats me and my dad both turning it at once), and even that needed some elbow grease to reset.

I also thought of the piston, but I cant think of how I'd implement it. The cannon is over-under, the valve being on the barrel side, so theres not much room for an elbow and a tee. Unless I can somehow make a coaxial style piston, it'd be a very awkward shape.

Please forgive any prolonged radio silence over the next few days, but I'll check this ASAP if I can find myself a computer.
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Unread postAuthor: Jared Haehnel » Thu Mar 20, 2008 8:58 am

I've got a similar design and I am using a double co axial piston design. You would have to extend you barrel through the teen and you would probably have to buy all new fittings. I cut my chamber into two five foot lengths to make it a bit more manageable to handle. While your at it you might consider making it an interchangeable barrels since your cannon would have considerable more power with a longer or larger bore barrel.
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Unread postAuthor: Daegurth » Thu Mar 20, 2008 12:28 pm

personally i'd make it a dual-chamber over/under with a 2" porting piston valve. the dual chamber partly for aesthetics, partly for manageability.

basically something like the mega-launcher, but single valved. that's probably going to be the simplest solution in the long run; all you have to do is cut your chamber in half, buy a couple of new fittings, and make a piston valve- all easy and realtively cheap.

maybe not what your design concept was going for though.

@jared: how does a double co-ax work? are your chambers behind/in the same horizontal plane as the barrel?
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Unread postAuthor: Jared Haehnel » Thu Mar 20, 2008 12:54 pm

The duel chambers are parallel to the barrel. It took some playing with on paper to get the whole thing to work but it would give increased flow which would result in increase muzzle velocity. Its not much of an increase and that increase was found using GGDT so I might loose it somewhere else. The pilots are hooked together and the valve is actuated with a 1" sprinkler valve.

My goal was to create a high performance pneumatic.... I think probably going to be one of the biggest on the site.
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Unread postAuthor: Brian the brain » Thu Mar 20, 2008 3:01 pm

You could alway ORDER a bigger valve now couldn't you?
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Unread postAuthor: Jared Haehnel » Thu Mar 20, 2008 3:10 pm

Yes I could but that would required me shelling out additional money...
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Unread postAuthor: Brian the brain » Thu Mar 20, 2008 3:26 pm

I understand you want value for your money but your first attempt hasn't given you any.
For a little extra money, you will not only achieve your goal, you will also ensure yourself you will get something good in return that will eliminate the need to spend any more after that.
This means no more frustration ( think about going back to the shop again and again, hours spent, disapointment) for you and the certainty this project won;t cost you any more than it has to.
You will end up saving money
And that is what you really want right?
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Gun Freak wrote:
Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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Unread postAuthor: rcman50166 » Thu Mar 20, 2008 3:37 pm

Ah. I see you've stumbled upon the savings vs. quality debate. Been there, done that. Turns out the only way is to stop construction until the demands engineer a new solution or to just wait for the money. Either way waiting is a part of the solution. :x
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Unread postAuthor: Brian the brain » Thu Mar 20, 2008 3:56 pm

If simply going for cheap would be the best there would not be such a debate.

I´ve just noticed that , even though one would naturally shy away from spending more/money/at/once, it would have been smarter in hindsight.

I could have bought 30 factorymade valves for the mmoney I´ve wasted trying to perfect my own
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Unread postAuthor: Jared Haehnel » Thu Mar 20, 2008 4:02 pm

Do you know any one whom makes custom co axial piston valves in large diameters? If one is careful with the design and construction they wouldn't have to spend a ton of extra money to get it perfect.

And most of my stuff I had on hand already...
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