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The Two Inch Barrel Sealer (TIBS), a name I came up with so the title for this guy was less bland, heh. Originally completed a year or so ago, it was posted on Spudtech.
With the coming of spring weather I decided to improve upon several things that had been bothering me about this launcher. The chamber is 3" by 2 feet, the piston is housed in a 2" tee and is actuated by a 3/4" QEV, in turn piloted by a blowgun. It has a 1 1/2" female threaded adapter outlet, which is normally connected to my golfball barrel.
The piston was originally 2" Ultra-High Molecular Weight Poly-Ethylene (UHMWPE) rod, which worked beautifully. It has a coefficient of friction equal to Teflon, while being 10 times more impact resistant then bulletproof glass. The last 2 pictures on the top row show a top and side view of this piston.
Never being fully content, I decided to make a lighter air-tight piston using an o-ring and check valve. After some experimentation the final incarnation can be seen on the 2nd row of pictures. The piston is two 1 1/4" endcaps on a short length of pipe, with an o-ring sandwiched in between. The sealing face is a 2" 1/16 thick neoprene washer held on by a 1 1/4" fender washer and machine screw. Plumbed into the rear of the picton is my homemade check valve. Between the sealing face and o-ring are 3 equalization holes drilled into the side of the piston.
I had some trouble finding an appropriately sized o-ring because the gap between 1 1/4" and 2" pipe is fairly large. I eventually found one at NAPA auto parts, size 136 for those looking to build a similiar piston.
Likewise, I found it difficult to find a small spring check valve. I eventually ended up making one out a 1/4" male-male NPT-compression adapter, 1/4" female cap, 3/16" ball bearing, and a small spring
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The result? Previously I could only actuate above 25 psi, the old piston had too mush leakby and all the air would just rush out the blowgun. Now I can actuate all the way down to about 3 psi. Thanks to the o-ring and check valve, I can actuate the valve with something as puny as a blowgun, or even through the schrader I fill it through!
I'm extremely happy with this launcher, according to GGDT it can put a GB weighted to 180 grams at 125 psi and a 10ft barrel out half a mile. The only time I've found a GB fired out in my fields was at 20 psi, unweighted, and with only half my barrel on, and that was 500ft out.
TIBS Launcher (New Piston)
wow, very very nicely done. it kinda looks like mine, but with a bigger chamber and a much nicer piston. very nice cannon.
"physics, gravity, and law enforcement are the only things that prevent me from operating at my full potential" - not sure, but i like the quote
you know you are not an engineer if you have to remind yourself "left loosy righty tighty"
you know you are not an engineer if you have to remind yourself "left loosy righty tighty"
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mega_swordman
- Corporal
- Posts: 526
- Joined: Wed Nov 29, 2006 2:37 pm
- Location: Bay Area, California
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Wow! That is really clean. I see this is your first post here, but I take it this isn't your first cannon. Clean, weel put together, and certainly pwns the cannon I made. Welcome to the forum and a job well done :thumbup:
By the way, for anyone who cares, I am trying to finish up a cannon here so I should be able to post it soon. However, I am isolated here (in Switzerland) and don't have a good supply of parts. One summer rolls in I should be able to roll out with some more cannons.
By the way, for anyone who cares, I am trying to finish up a cannon here so I should be able to post it soon. However, I am isolated here (in Switzerland) and don't have a good supply of parts. One summer rolls in I should be able to roll out with some more cannons.
"Never tell people how to do things. Tell them what to do and they will surprise you with their ingenuity." George S. Patton
Hmmmmm..... time to update the ol' piston.... 
Thanks everyone for the compliments 
I suppose I could have put a check valve there, but I like having the ball valve to be able to control the fill speed. When I'm filling with a large compressor it can be difficult to fill to a specific pressure, especially if I'm trying to get repeatable results with my chrony. Also, I don't have to disconnect from my air source to stop filling, which makes reload cycles quicker.spanerman wrote:the only thing i would change, would be to have a 1/4' check valve instead on the BV on the filling portion..