Yet another topic begging for help: Metered propane edition
Posted: Mon Apr 04, 2016 1:55 pm
Several weeks ago I set out to build my first metered propane cannon and up until actually trying to fire it things were going well. Every system works: the meter pipe holds pressure and seems to vent into the chamber, the fan turns on, the igniter (made from a stun gun) can be clearly heard arcing, but nothing happens. Between every misfire I removed the barrel and flushed the chamber before giving it another go with the same results. I have two theories as to why this is, but before I go messing things up I figured it would be good to get more expert advice.
Theory 1: Due to faulty math I ended up making the meter pipe volume 58 in^3 (a ridiculously large number, I'm aware of this). I redid all the math following a guide on these forums using Boyle's law (p1v1=p2v2) and discovered that with my chamber volume of 188 in^3 that my meter pipe would only need to be at 2 psi. The only gauge I could find read from 1-100 psi so getting to two psi is a challenge and I imagine that its not particularly accurate. Based on this inaccuracy have I been flooding the chamber each and every time? If so should I make the meter pipe smaller so that higher psi is required and an accurate reading can be obtained?
Theory 2: Considering the fact I'm testing this thing in my back lawn, no projectiles have been loaded into the barrel when firing. I did put a giant wad of paper towels all the way to the bottom of the barrel to try and block up the chamber but could the gas be escaping? I figured that a completely 100% perfect seal would not be necessary due to the low pressure of the gas and the nature of the cannons operation, is this misinformed?
Any help regarding this problem would be greatly appreciated.
Theory 1: Due to faulty math I ended up making the meter pipe volume 58 in^3 (a ridiculously large number, I'm aware of this). I redid all the math following a guide on these forums using Boyle's law (p1v1=p2v2) and discovered that with my chamber volume of 188 in^3 that my meter pipe would only need to be at 2 psi. The only gauge I could find read from 1-100 psi so getting to two psi is a challenge and I imagine that its not particularly accurate. Based on this inaccuracy have I been flooding the chamber each and every time? If so should I make the meter pipe smaller so that higher psi is required and an accurate reading can be obtained?
Theory 2: Considering the fact I'm testing this thing in my back lawn, no projectiles have been loaded into the barrel when firing. I did put a giant wad of paper towels all the way to the bottom of the barrel to try and block up the chamber but could the gas be escaping? I figured that a completely 100% perfect seal would not be necessary due to the low pressure of the gas and the nature of the cannons operation, is this misinformed?
Any help regarding this problem would be greatly appreciated.