Air Cannon

[MartinDWhite]

I would like to build a tin can air cannon, and need some help. Please no lectures on HPA safety.
 
A tin can is 2.5 inch OD.  
3 inch 1/4 wall tubing for the barrel, probably 4 to 5 feet long. (if the tubing is welded, I will bore out the weld line, but I can probably get seamless tubing).
100-500 psi tank 2 to 3 feet long mounted under the barrel ( 6 inch 1/4 wall tube with caps welded on the ends ).
1 inch line from tank to barrel with two 90* and a valve

The valve is where I need help. I am thinking a dump valve? A metering or knock open valve would need a long duration to let enough air out to push the can out the end. I see butterfly valves at McMasterCarr but they are expensive and I can't find open/close speeds on the air and electric ones. Solenoids don't seem to have the flow rating that I would need. I also see ball valves at McMasterCarr and they are rated for 600 psi in the 1 inch size. If it will open fast enough I think it will work. I know I can't turn it fast enough by hand, but I think I could use a large spring to open it fast. A "sear" would hold the valve closed and when released the spring would twist the valve open.  

Has anyone built or seen one of these. Some details on a valve would be GREAT if anyone had them.
 

    Martin D. White

[Magnum]

Unfortunately I have no experience with building airguns..however I did see this cool idea awhile back   http://inventionshowcase.com/golfballlauncher.htm   .  Thought may help? Tony.

[EdNunya]

I use an "air cannon" to throw lines over trees for antenna supports for Amateur Radio..

Mine is made from PVC sched 40 pipe and couplings, end caps etc...  The "tank" is made from 3 in, one end cap and a 3 to 1.5 inch reducer.. Short section of 1.5 inch to the 1.5 inch ball valve.. Another short section of 1.5 inch to a 1.5 inch threaded coupler.. The barel is 24 inches of 1.5 inch..  ( made the barrel removable for 2 reasons, storage, and multi caliber...)  The 3 inch reducer is drilled for a schrader fill valve (tire type) and a gauge... Projecticles are made from 3/4 inch pvc end caps and a coupler..They have to be sanded down to fit the barrel... A loop of nylon line is put through both endcaps from the inside, before glueing up... 2 hose clamps hold the spinning reel to the barrel...

80 psi is the max I've tried in it... That will throw my projectiles, towing 10 lb mono around 120 ft and about 45 yds or so downrange at a 60 degree launch angle...  I've sued it down to 15 psi for little  "jump" over the obstical shots too...

It's a hoot..And the best method for stringing antenna supports I'ved used to date! Biggest drawback to using a ball valve, is you dump the entire tank at one time..you can make a better valve from a sprinkler remote valve..  I just didn't care to go through that much trouble for it..4 dollar (on sale) compressor from Harbor Freight, does the trick!


http://www.antennalaunchers.com/antlaunching.html

One link..You can get ideas from there


Have fun..be careful!

73
Semper Fi
Ed

[airgunandy]

My oldest son used to be into air cannon big time, now he's into paintball.

Anyway, he used to visit this forum all the time:
http://www.spudfiles.com/

Got a lot of info from it.
He used sprinkler valves on several cannons. He made some kind of piston valve out of a PVC "T" and some other stuff for one cannon.Probably got the directions from Spudfiles.
One cannon he made launched a 1" x 12" piece of steel rod about 75 yards. It would shoot that rod through both sides of a steel drum at 10 yards.
He made one that looked kinda like a bazooka that shot little Nerf footballs.

[howie1a]

You need to be very careful  with using PVC for any high pressure air we had a PVC line blow up when the boat yard I was working fo. They r used it for a 125 psi air line to supple the shop it was just dumb luck no one was it the shop when it let go the funny part is the foreman was told buy  one of the other workers that could happen since it happened where he worked before when at his old job they had a PVC line blow up too. PVC and hi pressure air is not a good idea. howie

[airgunandy]

Yeah, ya gotta watch how much pressure you use.
100psi max for schedule 40 PVC. 50 to 80psi does pretty good.

[kiwi]

For a valve that will handle the psi / open quick & have a high flow...
look at a boiler blow down or safety valve....
They are replaced quite often and are made of brass...look around at scrap metal dealers..
Repolish the seats and they should be ok for your use..
They also come in pnumaticly oparated..so you could plum them
into the air system though a 2 port punmatic solanoird..with can be either manual
or 12/24 volt though a switch from a battery....

Pete

[howie1a]

I just noticed I didn't tell you that the shop used schedule 80 not 40 and still had the air line blow up using only 125 psi in the system it's a good thing no one got either killed or hurt bad since we had shards of PVC flying all over the place they were found quite a ways from where the PVC pipe blew up  and this was a 3 inch pipe  howie