SpudFiles

LastXdeth wrote:I cannot find a butterfly valve anywhere in my local hardware stores and and called all of them to find out that they carry the same exact valves. They only have 1 inch ball valves, and the trigger handles are not even springs, so I have to trigger my launcher by turning.

Also, my propane tank has a 1 inch stock, and I'm afraid I cannot weld it for 2 reasons: 1)No welding experience 2)Don't know any welders.

Would a one inch ball valve be sufficient enough to accelerate a cabbage through a 6 inch wide (5-6 feet long) PVC barrel at least 15 meters if I fill the air chamber to around 90 PSI?

If you're in America or a country that has a decent eBay website, I would look for a butterfly valve there first. Every now and then you'll find a great deal on a large valve. I believe they also make PVC butterfly valves but you may need to ring up a few irrigation stores to find one.

Edit:

If you go on www.mcmaster.com, you can get PVC 3" butterfly valves for ~$120 or aluminium ones for ~$100. Hopefully you'll be able to find some cheaper ones on an auction website.

I just did the equations in GGDT - an awesome tool for calculating the power of pneumatic cannons which can be downloaded here: http://www.thehalls-in-bfe.com/GGDT/ - and it turns out that about a 1.5" or larger ball valve would be fine. In fact, burst disks may be too powerful for this sort of thing, if you plan on actually pressurizing your propane tank up to 90 psi.

It might be a good idea to taper the end of the barrel so that it will cut off the excess cabbage when the cabbage is shoved inside, as some cabbages are bound to be larger than others. This will also keep air from leaking around the cabbage when it's launched.

You may want to decrease your tank size. Using a propane tank is overkill in a situation such as this.

I was thinking low pressure for distance adjustment range with a large valve. This gives the option of low power if desired.

For example, a test for another contest included launching a ball a precise distance. Other than a little off to the side, I was able to dial in the distance. The same cannon can do several hundred yards.
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For short distance control, good pressure regulation is required.

Thanks guys! You guys have been a tremendous help! I have changed my design completely to something like this, and using a tee pipe to connect two air resevoir pipes and concentrating the air pressure into one barrel. However, I will be incorporating a lot fo what yall suggested. Oh yeah, i don't need to hit a specific range. I just have to hit at least 15 meters.

I wish I could do the more thoughtful designs that yall ahve mentioned, but I fear that I can't find the materials in time. I guess that is what I deserve for procrastinating.

Yes, I am American, but every since Physics came into my life, I have merged the metric system with the Imperial ssyem.

Try to find a 3 inch sprinkler valve for that design. I also recommend an ABS chamber to prevent an explosion.
[youtube][/youtube]

Here is why I recommend a large valve. A small valve on a large bore doesn't work well.
[youtube][/youtube]

Would a one inch ball valve be sufficient enough to accelerate a cabbage through a 6 inch wide (5-6 feet long) PVC barrel at least 15 meters if I fill the air chamber to around 90 PSI?

I severely doubt it.

They only have 1 inch ball valves, and the trigger handles are not even springs

No ball valves will come with springs. You have to do that yourself.

Edit, sorry I didn't see the third page lol

And yes GGDT is nothing new around here, but it's good to know that a new member actually uses it

Gun Freak wrote:

Would a one inch ball valve be sufficient enough to accelerate a cabbage through a 6 inch wide (5-6 feet long) PVC barrel at least 15 meters if I fill the air chamber to around 90 PSI?

I severely doubt it.

They only have 1 inch ball valves, and the trigger handles are not even springs

No ball valves will come with springs. You have to do that yourself.

Edit, sorry I didn't see the third page lol

And yes GGDT is nothing new around here, but it's good to know that a new member actually uses it

That was wuite discouraging, but it did made me change my mind. I guess I'll attempt to find a welder to cut my propane tank to a 4 inch fitting and order a 4 inch buttefly valve from eBay. The thing I am worried about is cutting the propane tank.

Gun Freak wrote:And yes GGDT is nothing new around here, but it's good to know that a new member actually uses it

I think danielrowell was pointing out to LastXdeth, and not us, the existence of such programme

I still think burst disk is the best way to go, especially in terms of fps/$.

http://www.ebay.com/itm/4-CAMLOCK-FITTI ... 1e61c90e8c

http://www.ebay.com/itm/4-CAMLOCK-FITTI ... 1e61c91e75

Using camlocks greatly speeds up the reloading process, and looks cool. Yes.

LastXdeth wrote: The thing I am worried about is cutting the propane tank.

The welder can purge it with Argon or CO2. Propane in the tank will not burn without oxygen. With a oxygen depleted tank, the fumes when welding may catch of fire outside the tank, but that is minor and does not go boom. I welded mine with no issues other than a minor flame above the pipe from heating oil residue in the tank.

Lol, I'm back again. my dad is getting mad at me for procrastinating, so I'm going to have to be simple again. I'm just going building something like this using either an 8" or 6" rated PVC pipe as the air chamber and a 6" as a barrel. In between the pipes will be a butterfly valve that I found off eBay using MrCrowley's suggestion.

Once again, yall have supplied me with a wealth of knowledge!

Have you thought about making a combustion cannon?

No valve worries, you can make it out of a single tube combining barrel and chamber, and still get fantastic performance.

Combustion, internal or external, are not allowed, unfortunately. That would be too easy .

I will still receive major credit for constructing a pnematic launcher for effort, even if it does not hit 15 meters, but I don't want to feel like a guilty loser.

In that case I would defintiely recommend the burst disk option, it's the next best thing

I second what JSR says; go with a burst disk. All you need is a pressure-rated PVC union and some material for the disks. Search "burst disk material" on the Spud Wiki and it'll give you a list of materials and their approximate pressure ratings.