SpudFiles

how cold should i let it get before i quit using pvc for my cannons?
i live in ohio, very cold winters

Typically as soon as you need a jacket you should stop. So when the temperature is below 55.

ok thanks wasnt sure better safe than sorry, wont stop me in small diamiter haowever the combustion cannon i out of the question for the winter.

PVC doesnt get weaker, just more brittle, a fast opening valve or shock to the pipe(like dropping it or a piston valve opening) can cause it to crack and pressure will do the rest. So I would not use any piston valves or other high speed valves.

Sorry to cut in, but if i store my cannons in the house and they are room temp. would it be safe to fire them like 3 or 4 times and then bring them back in side to warm up again??

-BFC

Well maybe, would you be filling them with cold air and what temperature? As long as you dont drop or "shock" it you should be fine. Also I would not use any piston valves at all.

I was thinking more of my propane combustion cannons

To give you an idea, just let a piece of 1.5" pipe sit outside in the temperature you want, and smack it with a hammer. Compare how easy it is to break with a pipe at room temperature.

Not exactly scientific, but it'll let you know what you're dealing with.

As long as the chamber is kept reasonably warm on a combustion you'll be fine. Shooting it kinda takes care of that for you.

alright thanks,

I like science experiments, so I will definitely do the "smash" test. haha

-BFC

At lower temperatures the pipe can actually handle higher pressure, but it's impact resistance is lower. In a pneumatic the force of a piston hitting the PVC or a drop could put you in a nasty situation.
In a combustion this is not a problem because the "shock" is evenly distributed around the chamber and typically does not reach the rating of the chamber. The heat from combustion should stop the cannon becoming so cold that it does not behave in a predictable fashion, so you should be fine so long as you're sensible.