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Triggered burst disc question.

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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Triggered burst disc question.

Unread postAuthor: thespeedycicada » Sat Nov 24, 2007 1:15 am

Im really sorry if there is an easy answer to this but i searched and didnt find anything about this although im sure i read about it once i just want to be sure before i spend any money.
I was wondering if there would be a noticable performance increase if you put a burst disc in front of say a ball valve or even a sprinkler.I was guessing there would but would the burst disc just break before all of the pressure got behind it? thats what i want to know.
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Unread postAuthor: hi » Sat Nov 24, 2007 1:26 am

in front of a sprinkler valve, probably not. in front of a ball ball, yes.

in fact if it bursts slightly below the chamber pressure it would give you a noticeable power increase. I've never tried it, but I'm sure it would work.

if you going through all the trouble, why not just eliminate the ball valve and just use a union and a burst disk....
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Unread postAuthor: Eddbot » Sat Nov 24, 2007 4:17 am

i just had an idea :idea: what if you did what cicada was sayin and put the burst disk in front of the ball valve but as you're pressurizing the space behind the burst disk pressurize the space in front of but behind the ball valve, then you could take the burst disk to higher pressures before it broke, then to actuate it you just open the ball, the pressure behind the ball holding back the pressure behind the disk leaves, so the disk has to burst but it's at a much higher pressure, and your projectile goes alot faster. yes? no? maybe?
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Unread postAuthor: BigGrib » Sat Nov 24, 2007 4:33 am

why not just put a burst disk in between the ball valve and your ammo that way you can get the ball valve open a lot further before the disk bursts and the cannon shoots. might give you maybe another 10th of a second to get that ball valve open all the way before the burst disk goes. just a thought
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Yea, that's definitely going to get you at least a tazer.

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Unread postAuthor: jackssmirkingrevenge » Sat Nov 24, 2007 4:45 am

Eddbot wrote:i just had an idea :idea: what if you did what cicada was sayin and put the burst disk in front of the ball valve but as you're pressurizing the space behind the burst disk pressurize the space in front of but behind the ball valve, then you could take the burst disk to higher pressures before it broke, then to actuate it you just open the ball, the pressure behind the ball holding back the pressure behind the disk leaves, so the disk has to burst but it's at a much higher pressure, and your projectile goes alot faster. yes? no? maybe?


Eddbot, have you seen this?
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Unread postAuthor: Eddbot » Sat Nov 24, 2007 4:57 am

if we're tryin to get high speed actuation then we need a sprinkler or a better way to open ball valves faster, other than spring loading

edit: oops my bad, i got confused, then had a really old idea
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Unread postAuthor: Zen/// » Fri Nov 30, 2007 12:49 am

"I was wondering if there would be a noticable performance increase if you put a burst disc in front of say a ball valve"

Of course, just look at my sig... :lol:

I have a piece of tape as my burst disk (75psi burst pressure).
And a ballvalve with a chamber behind it (85-110psi). No matter what pressure bettween 85-110psi I use, there is a 1 second delay between ball valve actuation and the burst disk ruptureing.

Resulting in a preformance almost to that of HEAL (according to GGDT)
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Unread postAuthor: jimmy101 » Fri Nov 30, 2007 11:46 am

I was wondering if there would be a noticable performance increase if you put a burst disc in front of say a ball valve or even a sprinkler.

Maybe, maybe not.

The problem with a ball valve is that it opens slowly. As it is opening the air flow is severely choked. If the projectile starts to move while the flow is choked then you are consuming barrel without the full chamber pressure behind the ammo. In other words, there is too much pressure drop across the partly open valve.

If you add a burst disk, and the dead volume (volume between the burst disk and valve) is small, then the rupture pressure of the disk may be reached before the ball valve is fully opened. In worst case, the burst disk won't do anything at all since it may rupture when the valve is only slightly open.

It isn't so much a question of the rupture pressure of the disk as it is how quickly that pressure is reached with the valve only partly open.

EDIT:
Zen said:I have a piece of tape as my burst disk (75psi burst pressure). And a ballvalve with a chamber behind it (85-110psi). No matter what pressure bettween 85-110psi I use, there is a 1 second delay between ball valve actuation and the burst disk ruptureing.

Sounds like Zen's burst disk has a significant delay even after the pressure is above the rupture pressure. Sounds like the tape has to stretch for a bit before it fails.
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