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PVC pressure max

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Unread postAuthor: DYI » Sun Jul 06, 2008 3:26 pm

But a hybrid has an exponential amount of heat caused by pressure compared to that of a combustion

Do you even know what the word "exponential" means? An exponential relationship is " n<sup>x</sup>". Kind of like folding a piece of paper - the thickness can be found by 2<sup># of folds</sup>.

The pressure generated by various pre-ignition pressures is much closer to being linear than it is to being exponential. Not exactly, because of burn rate changes and such, but pretty close in ideal conditions.

A 2x mix should have about twice the energy of a 1x mix, and so on. If you'd ever fired a hybrid at 20x, you would have realised just how little heat is transferred to the chamber. And "making cool"? Every combustion gas gun I've ever seen was air cooled, and not even forced air. Just normal transfer of heat to the atmosphere until an equilibrium is reached. The chamber might heat up as much as 20 degrees or so on a high mix hybrid, but shocking up 20 degrees isn't going to have much effect on any chamber, nor is shock cooling by 20 degrees. The thermal effects on the chamber just aren't enough to worry about unless you're operating a hybrid at a few hundred x.
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Unread postAuthor: SEAKING9006 » Sun Jul 06, 2008 4:48 pm

As I said before, unless you're either on a volcano or for some strange reason blowing 200 degree air onto your guns, you won't have any problem with PVC heating up in a cannon to dangerous levels. You do need to worry about it getting too cold, though.

By the way, failures in bike pumps caused by heat are due to the dieseling effect, which absolutely cannot occur in any spudgun design to date. That being said, no-one has made an LGG-like design yet, in which dieseling is more than probable.
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Unread postAuthor: clide » Sun Jul 06, 2008 5:21 pm

burgerace69 wrote: :shock: hehe uh yes i actually am starting on a new hybrid project...the problem is that i cant weld...

They make a wonderful thing called threaded pipe and fittings. No welding required.

As for the temperature issue. PVC's rating is degraded by 49% at only 110 degrees F, a temperature that can easily be reached in a hot environment. It could even go well above that if the gun was sitting in the sun.

And although not related to the poster's circumstance. Bike pumps get quite hot by repeated compression of air. I have observed heating of a chamber by rapid firing a pneumatic gun. Enough to make me concerned about any prolonged firing. The hot end of the spectrum can definitely be an issue for spudders. Sure not in typical cases, but far before the scope of a LGG.
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