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Well this is my first post and my first cannon altho been constantly changing it.

I started with compression fittings and 2 2litre lemonade bottle which i tested and exploded at 125 psi every time

so slid 22 mm copper pipe into bottles then t junction then copper pipe then ball valve

now i have a co2 fire extingisher and found a male male fitting that screws into thread of fire extingisher then t junction with end cap with bike valve in then ball valve

so any idea on how much pressure the system can take using compression fittings / copper pipe
as i assume fire extingisher can take a lot of pressure

and any ideas of how to make faster opening valve as it looks quite hard trying to make piston valve using compression fittings

cheers

I'm just barely comprehending what you've got there. How about taking a few photos of your cannon and posting them here.

Yes a fire extinguisher can hold much more pressure than you should be working with at this point.

Let's see what you've got before we discuss faster valves.

Welcome to Spudfiles!

Any chance of some pictures, heres a piston valve how to that might work for what you want
http://www.spudfiles.com/forums/self-cl ... 17609.html

welcome to Spudfiles
a fire extinguisher used as a chamber can typically operate with more pressure than most can produce. Many fire extinguisher have threads that are compatible with 3/4" NPT at least for us in the US

do you have some pictures or something of your cannon or are you just describing them?
In terms of bottles:
Never use a bottle as a pressure vessel unless it was used for carbonated bottling a carbonated beverage even if they it has the same type of threads and cap. Your bottle had a similar bursting pressure of around 120-130psi as most soda bottle according to this source but stick to soda bottles because some companies might be cheap in their production.
Replace the bottle if you see white stress marks that will look like streaks, the plastic used will inevitably yield after being pressurized and depressurized many times. this doesn't mean it should never be used, after all a rupturing soda bottle has a very minor risk presented from dangerous shrapnel, just make sure you can replace the bottle and only use it below 80psi.

ok guys here is a few pictures

Where's your barrel? All you've got now is a really awkward airblaster.

Tighten up your assembly. Shorten the lengths of the copper pipe you have there, maybe get a QEV as a main valve (or build a piston), and make it look like its been thought about.

Right now though...ugh.

Try learning how to solder. Copper guns and piston valves go together like fat kids and cake, and from what I understand, solder copper fittings are easier to make a piston from.

ah ok thanks man

i have a barrel but its stupidly long so didnt have it on at the time i took the pictures

and for my next one i was thinking maybe solder joints. its just getting the money at the moment is the problem

and the reason the pipe is quite long is so that i can put it on my shoulder and use it without my arm being bent before i pull and valve open

any ideas on how to make piston valve for compression fitting?? as it looks like it will be quite hard

Your piston valve had better be hard, unless you're making it from gelatin.

All I can really suggest is to make a successful piston valve from PVC first, just to get the concepts down and to find what works for you. Then just see what you can do. You may find yourself standing in the plumbing section of your hardware store for some time, pieceing things together.

I can't imagine wanting to fire a cannon with your arm fully extended. It seems to me that an over under configuration would be more comfortable. With the piston valve, you'll have a pilot valve that actuates the main piston, so there's no need for a ball valve that far forward.

the pilot valve bit i have no idea what you said it what it does

and well only problem is i having fire extingisher under its very heavy and also the fewer turns i have the less energy is wasted as the air tries to get round the bend
not that it will really make that much difference i imagine

While an inline cannon configuration is generally more efficient (by minute differences), the weight of your chamber will be centered on the cannon rather than throwing off it's balance. This will ease the weight of it and also serve to shorten the length of your cannon.

If you don't know what a pilot valve does, I'd suggest you do some more research on piston valves before committing to building one.