SpudFiles

Heres my first Pneumatic. I didnt have enough money, for a sprinkler, so i used a ball valve. It is 1'' pvc(its pressure rated, if you dont belive me check the last pic.) the chamber is 14.5'' long, and the barrel is 36'' long. i would hev made the chamber bigger, but i didnt have much pipe to work with. I am using my hand pump to pressurize it, but i can only pump twice, and i measured only 45psi. Will i get more pressure from a compressor? Thanks. Im going to paint it as soon as i can.

Very clean work.
The chamber is a little on the small side, a simple 12v compressor will be able to get this to 150psi very easy. I think you may need high pressure in this to obtain results better a glove gun though.
Nice for what you had to work with

Why can't you push it past 45 psi? A run of the mill bike tire pump is usually rated for 160 psi, and you should be able to hit that and more easily unless you're a small child or a cripple. I've wrecked loads of those pumps by hitting over 200 psi with them, and I only weigh 130 pounds. No cheap compressor will give you more than 155 psi, and even that will cost you a lot more than a $20 bike tire pump. Refrigerator coolant pumps can easily exceed 300 psi, but they're a bit hard to come by, and generally expensive in North America.

And I'm not going to say that it's a nice cannon, because I'd be lying. Unless it's actually reverse optimized for the worst performance possible. It needs a longer barrel, more pressure, a faster valve (or at least spring loading), and a safe construction material. PVC is essentially the worst commonly available piping to build a cannon from.

thanks. I got a couple good shots off today. They were pretty powerful. Im gonna try a small compressor we have, and if it works good i will get one, because the one we have has to be plugged into a ciggarete lighter. I will have to stay below 150psi, because the pressure rating on the ball valve is 150psi, which means it fails at that pressure right?

If the ball valve is rated for 150 psi, it should have a failure pressure of slightly over 450 psi. Burst pressure isn't actually printed on parts, because some idiot might think they can use it within 5% of that pressure safely. Since people can't be trusted to include their own safety factor to fit the application, they take the average burst pressure, divide it by a set number (often 3), and use that as it's rated pressure.

DYI wrote:Why can't you push it past 45 psi?

A hand pump (like you might carry with you on a bike trip in case of a puncture), rather than a floor one, is hard for anyone to push past about 60 psi.

I have to agree with DYI, this cannon isn't exactly optimal. It's not a bad start, but for a cannon in that size, with that valve, the energy is likely to be no more than about 15 to 20 ft-lbs, and probably more like 12, which isn't a lot.
You need a quicker valve, and more pressure to get much out of a launcher.

Muzzle energy in Joules divided by barrel volume in cc gives average effective pressure (multiplied by 145 - not 14.5 - to give units of psi), a good measure of a launcher's power relative to it's calibre and size.

Your launcher has a very low figure of ~5 psi - Compare that to an advanced combustion with a value of ~30 psi.

ive only had it for 2 days, and my hands already hate it, because of the stupid ball valve. I would be happy if it just had a bigger handle. I couldnt use the compressor today, so tomorrow, i will pump it all the way up. I do agree its not a great cannon, but this is all the bigger the piece was. Next time its definately gonna be a sprinkler. I dont know there might not be a next pnuematic. Since my first experience didnt go so well, i might go combustion, i dont know, i guess im just venting, and trying to relax. sorry about my rambling. I guess i just wish i had thought things trough a little more.

BrodMan wrote:I dont know there might not be a next pnuematic. Since my first experience didnt go so well

What did you think the first one was for?
Look at my examples.

This is my first ever spudgun:


This is my latest, made only 3 months after the first:


The first one is supposed to be crap, unless you're a God of Spudding of course. Don't give up so easily.

I agree with Maxus it is not the most optimal design but it's alright for a start...
first you have to get a better pump since 45 psi is rather low pressure... also you should use better valve for you next gun - ball valves are not bad in general but those for PVC suck... of course you can switch to steel pipes or copper but that would make sense only if you could get it cheap and you had one of the most useful tool for steel spudguns - a thread cutter
sprinkler valves would be ideal if you want to use pvc

Pneumatics are far, far simpler to get working than combustions. Build a few good pneumatics and improve your building and designing techniques before you attempt a combustion. They can be a real b*tch to get working properly.

Don't give up because of one failed project, you just have to cut your losses and move on.

POLAND, why would you need a thread cutter? All steel pipe I've ever seen comes pre-threaded, or is cut by the people at the store.

I dont see what is so bad about it I actually like the design I might have to recreate that with a sprinkler because i like it so much.
I just really like extremely simple guns they are just easier to work with.
Trust me my first was worse.

Edit: HeHe that rymes

The only pre threaded pipe are nipples, which can be big enough for a small cannon, but if you want a big metal one, you are going to have to cut threads into the pipe.

Not really you just use a lot of nipples. Like in the SCTBDC.
tread cutters cost a lot of money and it is probably cheaper just to use a bunch of nipples and couplings unless you are planning to make a lot of metal cannons.

If this is your first then CONGADULATIONS on your first.....don't let the geek squad get you down.

We all started some where and in fact my first combustion gun actually self-combusted

It was a hair spray gun with a match hole. I loaded it, primed it with fuel, and stuck a match over the hole. No ka-boom....so I left it in the sun and it caught it self on fire and melted.....

That was a long time ago and now I build pneumatics. Just keep reading and posting and some day you will be the one with the knowledge (and cool cannons) and you will be the one thrashing some young spuder!

jr wrote:If this is your first then CONGADULATIONS on your first.....don't let the geek squad get you down.

We all started some where and in fact my first combustion gun actually self-combusted

It was a hair spray gun with a match hole. I loaded it, primed it with fuel, and stuck a match over the hole. No ka-boom....so I left it in the sun and it caught it self on fire and melted.....

That was a long time ago and now I build pneumatics. Just keep reading and posting and some day you will be the one with the knowledge (and cool cannons) and you will be the one thrashing some young spuder!

wow... how hot was it that day? something tells me it lit but didn't fire, and slowly melted after you walked away from the match flame and not the sun