SpudFiles

hi i am not wanting to make this it is a question i need answerd its been stuck in my head for weeks but what would happen if on a combustion gun right after the reducer there was say a ball valve(or any valve) you close the valve put a potato down the barrel open the back and put fuel in close the back and hit the sparker what would happen would it turn into some pneumatic gun so all you do is open the valve and the potato shoots out

Or turn into a hand grenade... in your hand

The simple answer is no, it will not work as you intend. The pressure from the combustion is short lived. Wait for someone else to explain the science.

I've had something similar happen with my combustion launcher. Overloading the barrel with a bunch of rocks (too heavy) or even dipping the first few feet of the barrel in the pool. Once fired I believe it creates a vacuum, from the sound of it, and the end cap requires a wrench to get back off.

RBurke83-
Not likely. I believe a contained explosion produces slightly more pressure, then a successful launch. Reason being the peak pressure is never reached because of the chamber volume increasing as the projectiles moves down the barrel and eventually exits.

I was never planning on doing it but that is interesting what would happen if you open the valve then(if you can get it open)

The question has been asked before, and I'm sure someone has given an educated answer. So, been searching for a while, and this is all I could find. Not the best, but whatever.

http://www.spudfiles.com/forums/contain ... t4876.html

ok that is what i was kinda what i was looking for

An automatic valve that pops open near peak pressure can improve performance if the addition of the valve does not hinder performance due to added flow restrictions.

See threads on Piston Hybrids for more info.

You might want to read http://www.inpharmix.com/jps/Chamber_Temperature.html

Short answer: Roughly one second after ignition the pressure in a closed combustion chamber is basically back at atmospheric pressure. To get any performance out'a the gun you'll need to get the valve open in much less than 1 second after igniting the fuel.

The only practical way to do that is with a bust disk.