Quote:
Originally Posted by ab500
I think I'm starting to get a much better idea of what needs to be done to improve this cannon.
First off to all the people who come into this topic to discourage PVC pipe usage:
PVC pipe is not the final solution!  We are planning to move away from it for later designs. This was merely the first prototype. In my opinion the way we were using it was perfectly safe. We are going to move to a more appropriate storage tank eventually but theres nothing like getting your feet wet first and PVC was the cheapest, most avaiable material out there. The barrel will probably remain PVC but I don't honestly see the material failing... there's a large hole in it where the balloons exit and I'm quite sure the pressure will force it's way out that way than through the side of hte barrel. |
I am very happy to hear that PVC is not the final solution for your tank. PVC gives almost no indication before it fails and when it fails, it fails violently when used in pressure applications.
What really concerns me is that the barrel will still be made of PVC. Your statement ("
I'm quite sure the pressure will force it's way out that way than through the side of hte barrel") tells me that either you don't understand the gas laws or are just not believing they apply to your cannon.
Gas exerts it's force in all directions at once. So when you introduce the gas to your barrel the force that starts to move the balloon also is applied to the inside walls of the barrel. PVC is not designed to take that sort of shock load and will eventually fail ... catastrophically (sp?), and generally without warning. Only once the projectile (Balloon) leaves the barrel will the pressure be relieved from the inside of the barrel.
Sorry to be such a stickler, but PVC and pressure generally equal someone taking a trip to the hospital.
Now on to the fun stuff
For the firing valve, why not use a
butterfly valve? Their CV is very high. The only drawback is cycle speed (which is not relevent here).
Also, any regulator you use (IE from SCUBA) will restrict your airflow. Your better off charging your tank to your firing pressure and then dumping through a large orifice valve directly into your chamber.