piston cannon building troubles

[Marffy]

I just tested my cannon for leaks underwater and it has 3. these three are at the main galv. air tank at the 3 major 2" joints. at the coupler (Both ends) and at the end cap) i put about 4 or 5 raps of teflon around the threads and i was wondering if i should crank the joints down and see if the tapering makes a seal or if i should unscrew, put more teflon, then crank it down. (please keep in mind it has to hold 300psi +. ) But doing that is hard, it was hard enough threading them together, now i must unthread them . Also, What is the best way to thread large pipes together? My pipe wrench can only rap around the smaller reducing bushing and i have no adjustable (cresent) wrench big enough, nor will my vice (table clamp) hold the pipe properly because it broke (yah, its hard to do but possible) But, i do have one other vice that is really big but not mounted to anything yet...

I am also wondering what cannon would be more powerful at 100psi? this one:http://www.spudfiles.com/forums/simple- ... 20136.html or the piston cannon in the picture attached? (assuming it is finished)

[jrrdw]

Try to tighten it all up before taking it back apart. You can use a "strap wrench" on the bigger pipes. Don't have a strap wrench? Use a old leather belt and a stick for a handle....play with it you can figure it out.