Mechanically actuated quick dump valve

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Labtecpower
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Mon Oct 26, 2020 4:55 am

To get myself to build some stuff again I decided to slap a cannon together in my lunch break, with all designing and calculating done on the fly.
I noticed that the projects where I spend a lot of time designing and preparing often don't actually end up being built at all..

Basically this is a quick dump valve cannon based on the first one being built by technician1002, and a previous version I built myself. Got a bit fed up by the pull-rod trigger, and wanted to shoot it like a normal airgun. Some coil springs to pull the piston backwards and a trigger system took care of that. Opening time is pretty fast because of the springs, and is sped up even more when compressed air gets in front of the piston. I had to redo the piston bumper as the cannon got smashed apart, shearing off M6 bolts in the process. Now it is equipped with an air brake to slow down the piston gradually. Heavy projectiles at 15 bar of pressure are not a problem anymore.

The bore is 60mm (barrel missing in the pictures :P ), I didn't calculate the chamber volume, but it is somewhat smaller than the barrel volume making for a relatively quiet shot.
It's still a bit rough around the edges, might fix that later if I feel like it. A shoulder stock, some basic sights and a bipod are still on the to-do list.
IMG_20201026_103931.jpg
IMG_20201026_103954.jpg
A look down the bore, showing the piston and valve ports
A look down the bore, showing the piston and valve ports
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Moonbogg
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Mon Oct 26, 2020 1:02 pm

Nice work. I've always loved Tech's QDV style and it's good to see a nice cannon made with it. Any chance of internals pics? Maybe a video seeing it shoot? Is the chamber stainless steel? It looks nice.
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jackssmirkingrevenge
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Tue Oct 27, 2020 5:12 am

Ah, very good to see you're still in the game!

You can clearly see the "I grew up on PVC but I'm an adult with access to metals now" pedigree :D
Got a bit fed up by the pull-rod trigger, and wanted to shoot it like a normal airgun. Some coil springs to pull the piston backwards and a trigger system took care of that. Opening time is pretty fast because of the springs, and is sped up even more when compressed air gets in front of the piston.
Personally I think letting the air do the work is a more elegant solution, by having a spool that is only slightly unbalanced, the trigger sear will not be very stressed even at high pressures and it takes less effort to cock too.

Image
Maybe a video seeing it shoot?
Hear hear!
hectmarr wrote:You have to make many weapons, because this field is long and short life
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Labtecpower
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Tue Oct 27, 2020 7:31 am

Any chance of internals pics?
Will take them when something inside needs fixing, shouldn't take long :P

The chamber indeed is stainless steel, it's an old helium tank I rescued from the recycling bin at my employer.

You can clearly see the "I grew up on PVC but I'm an adult with access to metals now" pedigree
It's simple and enjoyable, something I forgot to appreciate over the years hehe

I'm currently designing a "big bore" (9mm) piston hybrid, with on-board air and fueling. I should be able to get quite some shots from a 200cc reservoir filled to 200 bar if I stick to a relatively small chamber volume.
The goal is to have big-bore airgun power, but not the outrageous air consumption that inevitably comes with them. Currently thinking of a mechanical regulator that would enable me to fuel it with the press of a button. Will post it here as soon as I have a diagram.

For testing purposes i'll use 9mm ID hydraulic pipe as a barrel, but I'm eyeballing a 9mm Lothar Walther barrel blank in case everything works out fine.
Personally I think letting the air do the work is a more elegant solution, by having a spool that is only slightly unbalanced
I like the idea behind that, gets rid of the springs used in my design. However it sacrifices the simplicity of just grabbing a seamless tube and milling some ports into it which I like :P
Could be solved by sleeving the pipe on the inside with a tube with a slightly thinner diameter and an O-ring groove machined on the outside though, which shouldn't be too hard to implement in this design..


I'll make a video as soon as I can find a proper place to shoot this thing, i don't have a backyard anymore which makes life a bit more complicated.
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jackssmirkingrevenge
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Thu Oct 29, 2020 6:44 am

Labtecpower wrote:
Tue Oct 27, 2020 7:31 am
I'm currently designing a "big bore" (9mm) piston hybrid, with on-board air and fueling. I should be able to get quite some shots from a 200cc reservoir filled to 200 bar if I stick to a relatively small chamber volume.
The goal is to have big-bore airgun power, but not the outrageous air consumption that inevitably comes with them. Currently thinking of a mechanical regulator that would enable me to fuel it with the press of a button.
I don't know if you've been following what hectmarr has been doing with self-contained hybrids, definitely shows that with a bit of thought amazing things are possible even with limited resources.
hectmarr wrote:You have to make many weapons, because this field is long and short life
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