SpudFiles

Im making a cannon with a 8 to 10 inch diameter barrel all steel pipe from a 400 gallon air tank need valve ideas for it!!

make a combustion, a valve that big will set you back at least $100.

The only way to do it without wasting a lot of air would be to use a piston valve with a small pilot volume i think. Making it would be rather challenging though. I agree with hi, a combustion would save so many headaches- and in all probability be safer than a pneumatic of that size.
Let us know what you decide.

Edit: Welcome to spudfiles baby

If he's making a gun that big, money probably isn't really an object. The barrel alone will cost more than your average launcher does.

In my opinion, if you want really ridiculous power, you should go for the following setup, or something similar: Get four 8" flanges, and make a pressure differential operated triggered burst disk cannon. You could make burst disks out of sheet steel, since the flanges have a flat sealing face. Basically, you have a main pressure chamber, connected to a smaller chamber, with a flange in between, and then another flange between the small chamber and the barrel. Put a burst disk in each flange, and fill the small chamber to say 3/4 the burst pressure of the disks. Then fill the large chamber to slightly over the burst pressure of the disks. They will not burst because the pressure differential is still lower than the burst pressure. To fire, simply release the air from the small chamber, and both disks will burst immediately, releasing all of the air instantly through an unrestricted opening.

Please beware that this design will probably result in an unimaginably high noise level if your barrel is to short.

Your next best option would be a 10" pneumatically actuated butterfly valve, which will have far lower performance, and will set you back at least $600.

I say that DYI has the best idea, I think a single stage burst disk would also work good too, but its reliability would be touchy.
sheet metal could get expensive after a while.

I'd Say a piston piloted by a sprinkler valve.

Or you could just try and use the world's biggest sprinkler valve

I don't get it redcoat?
Is the whole gun like a sprinkler in that is acts in relocating water?

Yes it is. It's a dragster, it's not mine. I'd like to know how it went though.

im thinking about making a butterfly valve for the cannon using a car hood spring to help open the valve quickly im a machinist so i have the tools and would b able to get material cheap that will probably be the best way

Aren't butterfly valves really slow-opening? If you have access to a lathe, build a piston valve. Unfathomably small opening time....okay its really a couple of milliseconds, but you get the picture.

babyJ wrote:im thinking about making a butterfly valve for the cannon using a car hood spring to help open the valve quickly im a machinist so i have the tools and would b able to get material cheap that will probably be the best way

A butterfly valve could be hard to make so it seals well, but I would recommend pneumatic arm to operate the valve instead of a spring, otherwise I would recommend building a piston valve.

I cant imagine the power a 10" piston valved cannon would have...
A piston valve would get you the most power.

Redcoat wrote:Yes it is. It's a dragster, it's not mine. I'd like to know how it went though.

It's not the world's biggest sprinkler valve, it just has a normal 1" valve on it. Shooting water doesn't mean its a sprinkler valve.

why not make a burst disk out of a 2 liter bottle then have an electric actuator poke a hole in it. it be cheap easy and powerful

Redcoat wrote:Yes it is. It's a dragster, it's not mine. I'd like to know how it went though.

Well, I know the guy who made it, but how is it a sprinkler valve when its a dragster?