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Valveless pellet rifle.

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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Valveless pellet rifle.

Unread postAuthor: ALIHISGREAT » Tue Jul 29, 2008 6:22 pm

after seeing the patent for the valveless gun again thanks to JSR (http://www.google.com/patents?id=2hcxAAAAEBAJ&printsec=abstract&zoom=4&dq=Projectiles+to+trigger+avalanches)

i decided i needed to make one! (then came the relization it could and probably will be very hard!)

so i have just been throwing a few ideas round my head and the best i can come up with is:

a similar design and layout to the patented launcher where i would use ammo such as a flathead .22 air rifle pellet or a cylindrical PCP air rifle pellet (examples near the bottom of this page http://www.airgunbuyer.com/Showproducts.asp?cat=Pellets&SubCat=Pellets) or if i was to go larger, a battery or just anything cylindrical and with constant dimensions.

i would most likely need to construct the tee myself using some epoxy and aluminium tube to get a good thickness as the ammo would seal using an o-ring behind and infront of it. after constructing the tee and attaching the chamber i would most likely cast an epoxy block around it for extra strength.

as far as firing goes, the 'pilot' could just be a blowgun (or similar) hooked up to the chamber and then it would push the ammo foreward out of the o-rings.

as far as issues go... saftey is an obvious one because if an o-ring fails or it just doesn't work then an air rifle pellet would end up being shot into something... so i was thinking about a safety pin and a pin (probably a nail or something) would literally be put into two holes in the barrel near the end to stop a pellet coming out.

then there would also be the problem of mounting the o-rings inside the tee which so far i haven't thought of a souloution for unless i upscale so i could use a lathe to cut grooves (not possible in a ~6mm id tube :? )

so any thoughts and opinions on my ideas?
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Unread postAuthor: Mr.Sandman » Tue Jul 29, 2008 7:08 pm

sounds good but how high pressures are we talkin here
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Unread postAuthor: jackssmirkingrevenge » Tue Jul 29, 2008 11:50 pm

The concept is childishly simple and the theory is very sound - it's just a question of managing to translate it in practical terms and get your projectile to seal.

I had avoided o-rings by using the fact that a pellet's lead skirt expands under pressure when I made my prototype.
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Unread postAuthor: trollhameran » Wed Jul 30, 2008 12:59 am

It is alot easier than it looks...trust me, i made a slightly different valveless design with a 22mm copper barrel and I manged to get that to seal easily, using spud as ammo and no orings at all, http://www.uksgc.co.uk/forums/index.php?showtopic=1668.

I presume your making it with a small id barrel, if you wanted to go a bit bigger though, the Berol dry wipe markers are a perfect fit in 22mm copper.
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Unread postAuthor: ALIHISGREAT » Wed Jul 30, 2008 2:56 am

hmmm..... well i want to make one where the ammo is seated in a tee and there is nothing stopping it from exiting the barrel apart from the fact that there is no pressurized air behind it so the expansion of air rifle pellet tails isn't really a factor unfortunatly :( but i'm afraid it may come to a valvless design where the ammo has to be blocked as it will be much easier to do :?

as for pressure, i was thinking maybe ~300-400psi.

and i like your cannon trollhammerman but i'm surprised the spud sealed well :shock:
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Unread postAuthor: trollhameran » Wed Jul 30, 2008 3:04 am

I used a small copper disc infront of the spud to stop the trigger shearing the spud in half so i think what happens is the air pushed against the spud and squashes it so that it is forced against the sides of the barrel tightly.

What if you have a t and then have a rubber tube that fits inside it with a hole in the bottom a bit smaller than the ammo so that air can get through but the ammo doesnt fall into the chamber, then have your chamber coming off the bottom of the t and a small tube coming out the back of the t, which will have a blowgun attached and then some more tube going back to the chamber so that when you load the ammo the air is only pushing upwards on the ammo and not forcing it out, but when you open the blowgun a small amount of air from the chamber pushes the ammo a tiny bit from behind allowing all the air from the chamber to get behind it. If that doesnt make sense I will post a diagram later today.
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Unread postAuthor: ALIHISGREAT » Wed Jul 30, 2008 3:13 am

thats pretty similar to my plan, except i was going to use O-rings to seal the ammo, ill just draw a diagram!
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Attachments
valveless design.jpg
the red projectile is sealed on the o-rings infront of and behind it, then pushed foreward by either air or a pin to fire.
valveless design.jpg (12.96 KiB) Viewed 1369 times
valveless design 2.jpg
would it work with a rubber washer as a sealing face behind the pellet instead?
valveless design 2.jpg (12.62 KiB) Viewed 1369 times
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Unread postAuthor: trollhameran » Wed Jul 30, 2008 3:39 am

I would recommend using air to push it forward as it will be easier than sealing around a pin and stopping it from flying out the back.

It should work with o rings, the only reason I said to use a rubber tube instead was because it would give greater range of ammo,as it wouldnt have to fit exactly between to o rings
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Unread postAuthor: ALIHISGREAT » Wed Jul 30, 2008 4:18 am

after yet more thought, sealing against a washer at the rear would be much easier as i would only need to seat one O-ring.... if only lead was magnetic then i could use a magnet to 'pull' the pellet back into the washer to ensure a good seal.
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Unread postAuthor: jackssmirkingrevenge » Wed Jul 30, 2008 5:36 am

You'll need two o-rings, I don't really see the other design working.

One of the big disadvantages of this idea is that it strictly limits the sort of projectiles you can use - as in they must be cylindrical and rigid enough to resist being crushed by the pressure.

In this respect, burst disks are a better idea, and will offer similar performance in practice.
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Unread postAuthor: trollhameran » Wed Jul 30, 2008 3:42 pm

JSR: as much as I agree with you about the disadvantages of the design, im fairly certain for alot of people on this site, making new and innovative guns, and thinking up new ideas which will push the boundary's of spudding to a new level is just as much, if not more fun than blowing the s**t out of something with them, and you cant deny that the design (as with the majority of the ones you come up with) is awesome in that respect.
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Unread postAuthor: jackssmirkingrevenge » Thu Jul 31, 2008 12:33 am

I said there were disadvantages, not that it can't be done ;) if you look at my creations they're usually of this nature, so it would be hypocritical of me to stifle innovation.
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Unread postAuthor: trollhameran » Thu Jul 31, 2008 3:04 am

If it can be made to work well though, there are also some big advantages over burst discs, such as not having to buy tin foil lol. Nah the price of a couple of o rings (if you can get it to work this way) is about 50p, and you may need to replace them every once in a while, which is very cheap compared to pretty much all other valves. Also if you made it breach loaded with all projectiles a constant size then you could probably get a fairly good rof compared to a burst disc.

You may be able to tell, I am very keen on the valveless ideas.

Just had a brain wave, possible way of making it auto :idea:
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Unread postAuthor: trollhameran » Thu Jul 31, 2008 3:35 am

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not sure if this would work or not, I think it could though if you used something like marbles, as they wont crush and they are constant size. i took inspiration from a post you made in one of ants threads saying a genius would only have one moving part, the projectile. If you think it will work then ill knock up a prototype to test it.
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Unread postAuthor: jackssmirkingrevenge » Thu Jul 31, 2008 6:12 am

I had proposed a valveless auto here, it remains in the realm of my drawing board though.

The same effect can probably achieved in a simpler manner anyway.
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