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Better than a burst disk?

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Better than a burst disk?

Unread postAuthor: Combustion Monkey » Tue Jan 27, 2009 6:18 pm

I've been trying to figure out a way to get the effect of a burst disk without the hassel of replacing something between shots. I am thinking of building or buying a high flow pop-valve, something in the 1in size range. This would be mounted in the same location as a burst disk without having to be replaced between shots.

I have looked around a bit but haven't seen anyone trying this. If its a new idea (wich I doubt) or has been shot down for some reason I would like to know before preceding. As always any thoughts would be very appreciated.
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Re: Better than a burst disk?

Unread postAuthor: jeepkahn » Tue Jan 27, 2009 6:22 pm

Combustion Monkey wrote:I've been trying to figure out a way to get the effect of a burst disk without the hassel of replacing something between shots. I am thinking of building or buying a high flow pop-valve, something in the 1in size range. This would be mounted in the same location as a burst disk without having to be replaced between shots.

I have looked around a bit but haven't seen anyone trying this. If its a new idea (wich I doubt) or has been shot down for some reason I would like to know before preceding. As always any thoughts would be very appreciated.


You can get lightning quick electrically operated gate/guilotine valves all the way up to 6"+.... they ain't cheap though...
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Unread postAuthor: Combustion Monkey » Tue Jan 27, 2009 6:26 pm

Thats not a bad idea except for the fact that I don't want to add more electronics and price to an already pricy combustion :wink: . I would prefer to have it operated by the combustion gasses if its possible.
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Unread postAuthor: sputnick » Tue Jan 27, 2009 6:26 pm

I don't know, I would say build it, (of course)

I've never heard of the particular system you are referring to, but I assume its like, it *pops* open when fired then closes again when the gas stops flowing? or would you be willing to reset by hand, just not keep cutting tape?
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Unread postAuthor: jackssmirkingrevenge » Tue Jan 27, 2009 6:31 pm

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Unread postAuthor: Combustion Monkey » Tue Jan 27, 2009 6:33 pm

The valve would automatically close as soon as the pressure dropped. Give a look here.
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Unread postAuthor: Combustion Monkey » Tue Jan 27, 2009 6:38 pm

Interesting jsr. Perhaps if I were using ping pong balls it would work, but I would hate to spend the day grinding the dimples off all the golf balls I have :lol:
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Unread postAuthor: Hubb » Tue Jan 27, 2009 6:38 pm

I remember working at a hardware store through high school. I also remember seeing a special type of check valve there that had a "gate" on it. The gate would swing open, then close. It worked like a traditional check valve, but allowed for maximum flow.

These valves are called swing check valves (go figure) and look like this on the interior.
Image

Install this between your chamber and barrel. In theory, the spring (assuming it is set at the right tension) will hold the gases back until combustion is completed. The force will then open the check valve and allow the gases to do what they do. Once completed, the valve will close back.

Of course, there are some flaws with this. For one, getting a spring at the right tension. A little research and experimentation should fix this. Next, because the valve is closed all the time, exhausting the chamber may be an issue. Another installed valve elsewhere on the chamber should fix this.
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Unread postAuthor: Ragnarok » Tue Jan 27, 2009 6:41 pm

My suggestion to you is look up the QCTBDC (That is QCTBDC, not SCTBDC) - Quick Change Triggered Burst Disc Cannon.

It's an ingenious solution to the time taken to change burst discs, and regrettably, rarely imitated (in fact, I'm not sure it's ever been imitated).
Burst disc changes take all of a couple of seconds.

If I were doing a burst disc cannon, that's what I'd be copying - I'd look at different triggering methods, but for the burst disc holder, it's what I'd do without a doubt.

Given you're dealing with a combustion, the design would need some tweaks (as it uses static chamber pressure to hold the disc in place), but that's nothing that couldn't be fixed.
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Does that thing kinda look like a big cat to you?
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Unread postAuthor: jackssmirkingrevenge » Tue Jan 27, 2009 6:41 pm

Another alternative is to concentrate on making an extremely efficient piston valve with a light, tight fitting but low friction piston, minimal pilot volume and massive pilot valve.
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Unread postAuthor: Combustion Monkey » Tue Jan 27, 2009 6:42 pm

I saw those on McMaster, I'll have to give them another look. And by pure chance I happen to have a secondary exhaust port on the gun already.
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Unread postAuthor: Combustion Monkey » Tue Jan 27, 2009 6:48 pm

Ragnarok wrote:My suggestion to you is look up the QCTBDC (That is QCTBDC, not SCTBDC) - Quick Change Triggered Burst Disc Cannon.


I have built a quick change setup. It couldn't be more simple. The barrel on my gun is a full length coax. I simply tape up one side of a female to female coupler the way Starman does and slap it on the end of the barrel.

Edit: Slaps self for double posting
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Unread postAuthor: Hubb » Tue Jan 27, 2009 6:52 pm

Ragnarok wrote:My suggestion to you is look up the QCTBDC (That is QCTBDC, not SCTBDC) - Quick Change Triggered Burst Disc Cannon.


Yeah. It's too bad he doesn't post here anymore (or leave a bit more details on this design).
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Unread postAuthor: MrCrowley » Tue Jan 27, 2009 6:55 pm

hubb017 wrote:I remember working at a hardware store through high school. I also remember seeing a special type of check valve there that had a "gate" on it. The gate would swing open, then close. It worked like a traditional check valve, but allowed for maximum flow.

These valves are called swing check valves (go figure) and look like this on the interior.
Image

Install this between your chamber and barrel. In theory, the spring (assuming it is set at the right tension) will hold the gases back until combustion is completed. The force will then open the check valve and allow the gases to do what they do. Once completed, the valve will close back.

Of course, there are some flaws with this. For one, getting a spring at the right tension. A little research and experimentation should fix this. Next, because the valve is closed all the time, exhausting the chamber may be an issue. Another installed valve elsewhere on the chamber should fix this.


Instead of the spring, what about if you put a large ball valve after this valve on the right, and fill this valve with air pressure just larger then that in the chamber, so 120psi in the valve, 110psi in the chamber. When you want to trigger it, open the ball valve.

The slow opening of the ball valve shouldn't be too bad as there would be a small delay in the primary valve opening. Hopefully enough to allow the ball valve to fully open.


Edit: Just realised, the air inside the primary valve would probablt end up launching the projectile before most of the chamber air got to it.
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Unread postAuthor: Hubb » Tue Jan 27, 2009 6:57 pm

That would work, but not for a combustion :wink:

Edit: Just realised, the air inside the primary valve would probablt end up launching the projectile before most of the chamber air got to it.
Then it should be directed away from the projectile.
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