Hi all, I'm a newbie who's built a basic forge and have just recently started. I did a lot of research online on how exactly to set up a starter forge and built a passable version of Frosty's T-burner for it. I've fired it up a few times and after some small modifications I have a good heat (as far as I can tell), good pressure, and can work steel with it. My issue came up yesterday as I was working on a piece- the forge sputtered for about a second or two and then went back to normal. I checked the lines, pressure, and amount of propane in the tank (approx 3/8 full) and everything seemed normal. I went back to work, thinking maybe a breeze messed with the airflow for a second (I work outside) and when it happened again I decided to stop and secure the forge until I could figure out what was going on. I do NOT want to risk too much with propane if I don't understand what it's doing.
The sputtering looked and sounded like a loss of pressure or a change in the gas/air mixture- I could hear the difference (sounded like the vortex stopped in the forge) and I got 3-4" light yellow flames licking out the mouth of the forge. I do not get dragon's breath on this forge when running normally. The vortex then returned and the flames stopped.
My setup has a standard bbq bottle (20lbs?) running through a gauge, 30psi regulator, hose, and into t-burner. The burner is 1/2" diameter, but is scaled down in length to match the math Frosty listed in his diagrams. I am usually running the forge between 11-14psi and an hour or two at a time. At the time that it started sputtering it had run for about 45 min- 1 hour with no issues. No indication of icing; I read tank level at about 3/8th full. The parts are all relatively new so I don't expect to have a worn coupling, hose, or regulator. Not saying I don't, just that it seems unlikely.
My question to the group is what's happening here and is it a normal occurrence or something I should watch out for? My initial guess is that the tank level is lower than it should be, I'm losing pressure in the line and just need to refill. With low pressure I get no venturi effect and therefore no air coming in the burner, which would explain the dragon's breath. I assumed the gauge on the line would be correct, but in hindsight almost every gauge I work with at work needs calibration, so why shouldn't this one as well? If it did need calibration, shouldn't it just be a little off, though, and not enough to give me even a warning? At what level do most smiths with gas forges change out their bottles?
Erring on the side of caution until told otherwise.
Side note: I perused through the forum looking at other problems people have reported with their new forges and burners and I didn't find a thread that quite matched this. I could've missed it, so please forgive me for starting a new one if I did.