So it looks like your mash-tun has a rubber seal, the direct heat doesn't screw it up? Only the Guinness kegs come with the screw in bungs? All my kegs have the C-clip style. Again the detail on you system looks great!
Talon, It's the original o-ring I installed 6 yrs ago, never had an Issue, buna rubber is good to 175 and nitrle is good over 200, remember your only mashing at 150 -160 deg. very low flame just to maintain temp, the water is pre-heated in my other keg and then mixed with the grain to hit mash temp.
the European kegs have threaded bungs all American kegs have snap ring groove
one more thing for anyone thinking about converting kegs don't waste your time welding in nipples for ball valves
you will never get anyone to give you an inclusion free weld unless they are a robot, drill a clearance hole for a bulkhead fitting and use quarter turn stainless aircraft compression coupling (CPI) they can be disassembled in a matter of seconds for cleaning
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