air cannon

[John Zuber]

i am building a spud gun using air that is supposed to shoot a tennis ball about 50 feet (for a science project). i am going to use a ball valve to release the air in to the 2 1/2 inch barrel that is about 4 to 4 1/2 feet long. i need to know how big the ball valve should be and how big the air chamber needs to be to give me the best performance. thanks.

 

[Todd Z]

you want a small air chamber and at least a 1 inch ball valve.



We did this with drain plugs and a 1/2 inch ball valve and were able to go 100+ feet...



I think trial and error may work the best..



Todd Z

 

[Jason Sundown]

why dont you make one of those cannons from pvc piping and get a igniter like how they do the potatoe bombs. you get a long (at least 3 feet) pvc tube the diameter size of the average potatoe and then cap one end off it and then make a hole a few inches forward of the capped end and install your igniter. smash your potatoe in the other end as far as you can get it in to get a tight seal and put spray hair spray fluid inside tubing near the igniter and point , press the igniter button and it shoots pretty damn far with a wicked kick back. I don't know if this is what your trying to accomplish or you are trying to make something more sophisticated. One of my friends female cousin made this and I was having fun with it all day. I heard it was illegal to make though. But good luck with the project anyway.

 

[John Zuber]

jsundown, i am not allowed to use any flammable gases i can only use compressed air. and yes i already have one of those but was told not to use it.

 

[John Zuber]

Todd, my son did the original post...I was thinking the same about the air chamber. Small would provide high pressure, but short blast. But the question is..how small. Perhaps 2" dia and maybe three to four feet long?

 

[Todd Z]

IF you have the air flow let the ball be the seal and let the chamber fill up as it propels the ball...... meaning let the ball fall all the way to the bottom other wise you will loose pressure as it compresses the air in the barrel.....



3-4 feet is long enough....

Todd Z

 

[Terry Phillips]

Check the Link.

 

[Gavin Allan]

Big air chamber (assume for storage just before ball valve). Use highest air pressure that the pipe will handle safely (use schedule 80 pipe if you need to).



Biggest Ball Valve you can get. Better yet, use a big solenoid valve (cross/double ports for additional air flow) so that you can quickly slam the air into the gun.



Get the ball wet with something like 90wt gear oil so that it is lubricated, but yet gives a better air seal to the barrel.

 

[Todd Cloutier]

The size of the orifice in the valve between the chamber and the barrel is probably the most important factor. When the pressure differential across the valve is about 1.8 (that's the pressure in the chamber divided by the pressure in the barrel) you get sonic flow through the valve, and the velocity of the air through the valve cannot exceed the speed of sound. So, your flow rate is solely governed by the size of the orifice in the valve (this means that a larger valve is better).



A spreadsheet calculation can be used to design the air cannon.