Problem with propane potato gun
Posted: Fri Aug 15, 2008 11:01 pm
I just built my first spudgun today with mixed results. My measurements are as follows.
Combustion chamber - 4in PVC 24in long
Projectile barrel - 2in PVC 48in long
According to my calculations this should get my to around a 1.75:1 ratio of combustion chamber to launch barrel. My problem is that I cannot get it to launch at all. I had it go about three times, but I cannot find a common reason why. I'm pretty sure my problem is the way I have my propane hooked up. I bought a propane regulator meant to be used with a small screw in tank. From what it seems ,when I open the first valve to fill no propane comes out, only when I open both valves and turn on the regulator do I actually hear the gas. I think that the regulator is not designed for such a use, but I could be wrong. That could be one problem, another could be how the propane is brought in. The way I bring in the propane is through a 4in coupler with a t'ed reduction to 2in. I'm not sure if propane floats or sinks in air. It could be that the propane is staying in the fittings. Also for the grill igniter I used the stock piece how it came. It uses a 3 walled cage to shield the spark. This could be a problem as well, but I'm not sure. If you find any of those to be mistakes any suggestions would be great as well as any other concerns.
Thanks for your help,
Ken
Combustion chamber - 4in PVC 24in long
Projectile barrel - 2in PVC 48in long
According to my calculations this should get my to around a 1.75:1 ratio of combustion chamber to launch barrel. My problem is that I cannot get it to launch at all. I had it go about three times, but I cannot find a common reason why. I'm pretty sure my problem is the way I have my propane hooked up. I bought a propane regulator meant to be used with a small screw in tank. From what it seems ,when I open the first valve to fill no propane comes out, only when I open both valves and turn on the regulator do I actually hear the gas. I think that the regulator is not designed for such a use, but I could be wrong. That could be one problem, another could be how the propane is brought in. The way I bring in the propane is through a 4in coupler with a t'ed reduction to 2in. I'm not sure if propane floats or sinks in air. It could be that the propane is staying in the fittings. Also for the grill igniter I used the stock piece how it came. It uses a 3 walled cage to shield the spark. This could be a problem as well, but I'm not sure. If you find any of those to be mistakes any suggestions would be great as well as any other concerns.
Thanks for your help,
Ken