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Step Barrel / Potato burst disc

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Step Barrel / Potato burst disc

Unread postAuthor: jagerbond » Sun Apr 12, 2009 2:07 pm

I did some searches but have not found this discussed yet, feel free to re-direct me if it has.

The thought is to create a step in the barrel to restrict the potato until pressure has built up.

I was thinking to turn out a piece of schedule 80 2" so that the ID was same as OD on 1.5" schedule 40.

Specific to our breach loading BL-415 I was going to remove 3 of the 4 inches that the barrel sticks out of the back of our BL-415. Then, slide/glue on 4 inches of the turned 2". The 2" would be sharpened to cut the potatoes which will now slide in and be restricted by the step where the 2" and 1.5" meet. The restriction should allow pressure to build before the potato is re-cut to meet the ID of the 1.5 upon exit.

Thoughts? Will the potato stay intact? Pressure build up be to great and chamber failure?

Thinking a remote and blast shield protected test fire.

Mike
Sureshot Inc. / http://www.ultimatespudgun.com/
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Unread postAuthor: LCTChamp » Sun Apr 12, 2009 2:25 pm

If I'm not mistaken, I could be, 1.5" sch 40 already fits inside 2" sch. 80. I wouldn't bother with remote test firing if all your parts are pressure rated. Most combustions will produce under 100psi. As long as the 1.5"pipe is sharpened also, the potato should stay intact.
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Unread postAuthor: jonnyboy » Sun Apr 12, 2009 2:48 pm

I think it would work. 2 inch sch80 PROBABLY will not fit around 1.5 inch sch40. Seeing how 1.5 inch sdr 21 fits nicely in 2 inch sch 80 and it has a smaller wall thickness.

Although if your shooting potato's your not going for performance, and if you were you should be using burst disks coupled with golfballs or something a little harder...
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Unread postAuthor: c11man » Sun Apr 12, 2009 2:56 pm

it will fit EXACTLY the same as sdr 21 in 2inch sch 80....

it doesnt matter what sdr or sch a pipe is it will always have the same od

the only thing that changes is the inside diameter.

this is why sdr 21 fits is sch 40 fittings
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Unread postAuthor: jagerbond » Sun Apr 12, 2009 3:23 pm

lctchamp wrote:If I'm not mistaken, I could be, 1.5" sch 40 already fits inside 2" sch. 80. I wouldn't bother with remote test firing if all your parts are pressure rated. Most combustions will produce under 100psi. As long as the 1.5"pipe is sharpened also, the potato should stay intact.


I was thinking not to sharpen, keep flat for more restriction.

http://www.engineeringtoolbox.com/pvc-cpvc-pipes-dimensions-d_795.html

Looks like its .039" larger. Like stated, should work without modification.


Seems like a Chrony™ test is in order

Mike
Sureshot Inc. http://www.ultimatespudgun.com/
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Unread postAuthor: Sticky_Tape » Sun Apr 12, 2009 3:49 pm

APPLAUDS* That is a really great idea jager. I hope it works for you.
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You can tell how awesome a cannon is by the pressure used.
http://www.spudfiles.com/forums/high-pr ... 12803.html
xnt rnm ne z ahtbg
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Unread postAuthor: LCTChamp » Sun Apr 12, 2009 4:04 pm

I was thinking not to sharpen, keep flat for more restriction.


That may work the only way to find out is to try it. I used to not have my barrel sharpened and would just smash the potato into the barrel. It worked with decent performance, but the potato would sometimes split which would allow air to pass by. It might turn out similar.

c11man: Thats what I thought, because I remember thinking if I ever found a 2" sch 80 tee for cheap I could use 1.5" pipe for a piston.

edit: spelling and grammar
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Unread postAuthor: c11man » Mon Apr 13, 2009 9:00 am

you dont even need a sch 80 tee, all you need a a small peice of sch 80 for the guide tube because sch 80 and sch 40 and fit in either fitting

i also think that the potato may crack/turn to vapor when it tryies to go into the smaller pipe
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Re: Step Barrel / Potato burst disc

Unread postAuthor: SPG » Mon Apr 13, 2009 11:26 am

jagerbond wrote:I did some searches but have not found this discussed yet, feel free to re-direct me if it has.


In a bit Jack will come along and post a link to the old Spudtech forums where we discussed this for a bit.

Don't think anyone ever built one though, but can't remember if there was a reason why not.
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Re: Step Barrel / Potato burst disc

Unread postAuthor: jackssmirkingrevenge » Mon Apr 13, 2009 12:13 pm

SPG wrote:In a bit Jack will come along and post a link to the old Spudtech forums where we discussed this for a bit.

Don't think anyone ever built one though, but can't remember if there was a reason why not.


This one?

In a pneumatic, anything that delays projectile motion in the breech can only be a good thing as long as no gas blows past the projectile. In combustions though, if the projectle stays still too long, the burning gasses lose heat and therefore pressure and you could therefore lose power.
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Unread postAuthor: jagerbond » Mon Apr 13, 2009 2:57 pm

If the delay was fairly consistent then it may require a larger chamber to barrel ratio...?
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Re: Step Barrel / Potato burst disc

Unread postAuthor: SPG » Mon Apr 13, 2009 3:32 pm

jackssmirkingrevenge wrote:This one?

In a pneumatic, anything that delays projectile motion in the breech can only be a good thing as long as no gas blows past the projectile. In combustions though, if the projectle stays still too long, the burning gasses lose heat and therefore pressure and you could therefore lose power.


No, it was THIS ONE with dual friction barrels and internally chamfered breach knives, but a search of "choke" pulls up a couple of other ideas using O rings, or the simplest of the lot, using heat to slightly distort the tubing.

I seem to have gone on about the idea quite a lot back then didn't I?
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Unread postAuthor: King_TaTer » Mon Apr 13, 2009 3:46 pm

The thing is, as jack said, the pressure created in combustion is only held for a split second then dissipates. You would have to be able to control how long the projectile is delayed by the shift in bore size. This would require a lot of experimenting. Burst disks on the other hand would be a much simpler solution. Good luck anyways if you go for it.
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Unread postAuthor: LCTChamp » Mon Apr 13, 2009 4:29 pm

Burst disks on the other hand would be a much simpler solution.


The problem with burst disks is it makes the loading process a lot longer. With the design he has now there wouldn't be anything added to the loading process. I doubt his customers would like the idea of unscrewing a union or undoing a camlock and then having to cut the disks from foil.

As mentioned above your idea might cause a decrease in performance. But it would be pretty cool if you actually got it working.
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Unread postAuthor: SPG » Mon Apr 13, 2009 4:41 pm

EDIT:

Someone delete this, I just made what can only be described as one of those posts which states the blindingly obvious, deserves the reply "No sh*t Sherlock" and doesn't move us on one tiny bit.

In my defence, it's late, and I've had a couple of glasses of wine.

Night all.
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