Labtecpowers (soon-to-be) quick dump valve cannon

[jackssmirkingrevenge]

now your avatar make sense

I won't take random foot abuse from lightweight girls in gas masks!

*pauses*

Well, nevermind.

[Labtecpower]

The lip on the back of the tank will stay on, as it provides some protection to the filling valve.

To take away any rumours; im not a underweight girl with a gas mask fetish

[Technician1002]

I put the fill valve on mine up front so it has protection next to the barrel. If stood on the breech, the valve can't be damaged. If dropped on the ground with the barrel attached, the valve can't hit the ground.

If you did have high recoil, do you really want that ring hitting you?

[Labtecpower]

That's smart !

I can also hide it in my barrel supporting frame, to protect it even more.

I found a nice manometer, but I don't know what threads are used.
I searched a bit, and I think the threads are 3/8". Could I be right?

The threads are about 0.25 mm deep, and the overall diameter of the threads is 10 mm.


Your reply made me realized that getting by that ring could be pretty painful.


However, I think that cutting the ring off could weaken the tank. I will add something that won't hurt that much.

[Technician1002]

I cut the ring away with a hacksaw, then the remaining tabs on the tank were filed smooth. Here is a photo of my current build where the ring is cut loose from the tank prior to filing the tabs down. Later the top carry ring was cut off too.


Here is the tank with the top carry ring removed and the welds filed down to smooth bumps.


To prevent the welds from tearing holes in the tank or making weak spots, I cut the ring as shown. The black cuts were done first, followed by the yellow cuts. This left the welds on the tank without weakening the tank from stress. Then the tabs were filed down.

On my cut ring photo you can see the 3 sections of ring and next to the tank is one of the tabs that remained which was cut off.

[Labtecpower]

That looks like it isn't going to weaken the tank. I will try that.

also, i'm a bit worried about deformation of the valve pipe. I also want to cool it on the inside, to prevent the zinc coating to vaporize. Do you have any experience with this? I was thinking about putting a wet ball of toilet paper in the pipe.

The weld will be MIG/MAG.

[Technician1002]

Due to the heavy sanding on my pipe, I simply burned off the galvanization during welding on the 1 inch and 2 inch. The 2.5 inch was black iron. So no suggestions on prevention of burning of the coating. Your welder may have more insight on this.

Welding was done outside near a large box fan to draw away fumes. A box fan about 8 feet away to the side and blowing over the project does a good job at moving fumes away to the side.

On deformation, the ports on the one inch were fine as it was brazed instead of welded. On the 2 inch was brazed and the ports were placed about 1/2 inch from the brazing so it didn't have any problems either.

The 2.5 inch with the ports right next to the weld does have some distortion which I am still sanding out. It will clean up OK, but it will take some time.

[Labtecpower]

Some zinc loss doesn't matter, but I absolutely want to keep the inside smooth, as i'm a bit sick of sanding. (I sanded over 15 hours to remove the ridge)

The welding is done under a fume hood, so the zinc oxide vapor won't intoxicate the welder. I don't think putting a large fan near your welding job improves quality, as it blows away shielding gas.

You didn't experience deformation?

[Technician1002]

I did experiance some deformation on the 2.5 inch cannon which was welded. The other two were brazed and did not deform. I used a gas torch, so shielding gas was not used. For brazing, fluxed brazing rods were used.
Here is the brazing job on the 2 inch cannon.


The lack of distortion of the 2 inch valve is easy to see in this photo.

[Labtecpower]

I have also been thinking about welding a few spots, and solder the rest of the pipe for sealing it.

Was the deformation on the 2.5 inch cannon easy to sand away?

[Labtecpower]

The tank is welded on !

I asked the welder to keep the pipe as cool as possible. The zinc layer is barely damaged.
I also soldered on the filling valve.

I asked a teacher for a 1/8 gas thread tap, and I tapped some threads for my manometer. At home I put it in, and it is totally leak-free.

I slid in the piston, and started pumping. I couldn't fill it, because it leaked too much. Now i have put on some rubberbands in the O-ring groove to compress the O-ring against the valve housing. Now it doesn't leak very much.

I also found a leak in one of the welds, and I filled up the gap with some epoxy.


some pics:







I filled it up to 30 psi max.

The power is impressive. I was able to launch a piece of aluminium 10 meters away, with the gun on a distance of 1 foot.

The gun was filled to 10 psi at that shot

The garage doors rattled in their frames when I shot it

Tomorrow I will put on a barrel, and maybe do some test shots damage pics !

[Technician1002]

O rings should not require rubber bands under them to make a seal against the valve body. Try to find the next size larger o ring or be sure the inside of the valve body is polished smooth so it doesn't leak.

A small amount of grease or vasoline will take care of some very small surface imperfections to get it to pressurize. Once under pressure, the air pressure should take care of any o ring compression for a tight seal.

The first time you do a 100 PSI shot, you will be impressed.

[Labtecpower]

The cannon is finished now. I bought a barrel, and epoxied it in the fitting.

I shot the gun today, and I went up to 3.5 bar (50 psi)

As ammo, I used a golf ball with a tube taped to the back.
Without the tube, I think i'm getting more range, as the shots were completely out of balance (wich I find strange, because the same setup worked perfectly on my other gun)

The muzzle blast wasn't very loud, but the projectile made a sound similar to a jet fighter ripping trough the air

Range:

125 meters at 1 bar (14 psi)

150 meters at 2 bar (30 psi)

280 meters at 3.5 bar (50 psi)

[youtube][/youtube]

The projectile landed by the trees.



I also filled a small plastic bottle with sand, and shot it at a beer can at 4 bar (58 psi)
The bottle ripped the can in two, and went trough a small haystack behind it

I'm VERY impressed by the performance of this thing


I hided my face, as i'm not totally sure about the legality.

[Technician1002]

I've never found a golf ball when shot at 100 PSI on a 2 inch valve. Let me know when you try a 100 PSI shot. I do know the sound you are talking about. It is impressive. I was about 50 feet down range when an orange was shot. It passed me about 20 feet away. The sound was amazing.

[Gaderelguitarist]

Well I'm definitely motivated to build one of these now. I can definitely see the need for a horizontal grip at the breach.

You could have just worn a hat and sunglasses.