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chamber to barrel reducer design for high pressure ?

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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chamber to barrel reducer design for high pressure ?

Unread postAuthor: matti » Wed May 05, 2010 1:45 pm

Hi
I have been working with high pressure 50-200bar cannon, using the "QDV" valve design.
(if you dont know QDV, just think this as coaxial thing)

chamber is 316l stainless steel, diameter 88,9mm and wall thickness of 4mm (ID is 80,9mm) and one meter long. I dont have barrel yet, but it will be something between 30mm and 40mm diameter.

thing is that my 316l pipes can handle high pressures, but i need to find a way to connect chamber to barrel, so that it can take those pressures.. welding would be easy, but where I can find 88,9mm to ~35mm reducer that has 4mm wall, and would take 200bar.. cone shaped reducer is little bit bad for this design and pressure.

machining reducers from 90mm solid 316l.. lot of work and money, but can be done.. maybe thick aluminium reducers connected with bolts ?

..or making reducers by pressing them, out of 4mm 316l sheetmetal ? i think 250,000kg hydraulic press could do that..

and some of you at least understand that endcap/reducer desing has very big effect on the pressure that it can hold.. using good design you can get same thickness endcap to handle 100 times the pressure, then using just straigt plate as an endcap (think about wine bottle bottom). hmmm.. my engklishs is not wery good lol :D

any ideas here ?
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Unread postAuthor: jhalek90 » Wed May 05, 2010 2:13 pm

200 bar = 2,900.75475 pounds per square inch

Are you SURE a 4mm wall thickness SS chamber will hold that?

What is is pressure rated to?
Where do you get 3000 psi of Air??? Welding cylinders?
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Unread postAuthor: Hotwired » Wed May 05, 2010 3:50 pm

Why would you want to use a "Quick Dump Valve" on a large and extreme pressure cannon?
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Unread postAuthor: Gippeto » Wed May 05, 2010 4:25 pm

Hotwired wrote:Why would you want to use a "Quick Dump Valve" on a large and extreme pressure cannon?


What do you think the Avalauncher is?

Machined reducers, sealed with o-rings, and cross bolted are fine if you have the room to work it into the design.

You know how to calculate shear strength of a bolt?

Can help if needed.
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Unread postAuthor: Hotwired » Wed May 05, 2010 4:52 pm

Gippeto wrote:
Hotwired wrote:Why would you want to use a "Quick Dump Valve" on a large and extreme pressure cannon?


What do you think the Avalauncher is?


You do know you're saying that to the person who dug up the Avalauncher patents, then edited and coloured the mechanism diagrams then posted them here with descriptions of how it functions.

To be exact I'm interested in how the "QDV" would be implemented in this design.
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Unread postAuthor: Gippeto » Wed May 05, 2010 10:16 pm

:lol:

Fair'nuff then. :)
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Unread postAuthor: matti » Thu May 06, 2010 1:33 am

Hotwired wrote:Why would you want to use a "Quick Dump Valve" on a large and extreme pressure cannon?


why not ?

-high flow
-no need for pilot vale (large 200bar pilot valve would not be cheap)
-easy and "cheap" to build

this is a test cannon for heavy projectiles, not for fun potato shooting

If I need to change O-rings after every shot, thats OK..
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Unread postAuthor: Crna Legija » Thu May 06, 2010 2:17 am

well if you build it with tight tolerance (which you should when using insane pressure) you wont be changing orings every shot. I think that machining reducers held on with bolts is your best bet.
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Unread postAuthor: MrCrowley » Sun May 13, 2012 5:47 pm

matti wrote:why not ?

-high flow
-no need for pilot vale (large 200bar pilot valve would not be cheap)

Well you could always use a hydraulic-rated S/S ball valve to pilot a piston valve. Just putting it out there as a normal barrel sealing piston valve will retain its o-rings for longer.
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Unread postAuthor: jackssmirkingrevenge » Sun May 13, 2012 11:50 pm

matti wrote:-high flow
-no need for pilot vale (large 200bar pilot valve would not be cheap)
-easy and "cheap" to build

this is a test cannon for heavy projectiles, not for fun potato shooting

If I need to change O-rings after every shot, thats OK..


A burst disk valve would satisfy all the above requirements and would have no moving parts (except the fragments of the burst disk moving really fast down the barrel :D)
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