So a few weeks ago I dropped the lid of my old Presto on a concrete floor and it hit and smashed the gauge...and more importantly, cracked the aluminum around where it screws in! Ugh! The thing is probably seventy years old....and had been with me for twenty! So I go shopping on EBay for something similar, and found an "Old National #7" circa 1953, which looked similar, and at a decent price. It arrives, looks good, rubber gasket looks new, intact, and tight. So I put some water in it, otherwise empty, and bring it on up to 15 pounds by the old gauge as a test, just to be sure the seal was good, etc. (I was originally planning to probably replace the gauge, which looks like the original, or possibly exchange it for a weighted gauge like I have on my larger "All American") So I let the pot cool down and then go on to other things and come back to it next morning and the lid is stuck fast! When my other canner does this I give it a tap or two on the lid with a block of wood and usually it comes loose....not so this time. Eventually I take a hammer to the lid handles, trying to force it to unlock...no go....ended up cracking (and replacing) one of the wooden lid handles! Ugh! So I hit the internet....and so far here is what I've tried...heating the pot back up and then trying to undo the lid as soon as the pressure reads zero; pouring boiling water all over just the lid, not the pot; setting the whole pot out in the sun, and even in my larger solar cooker, for a few hours....; leaving it outside on a frosty night and trying first thing in the morning; taking an old syringe and injecting vegetable oil all along the rim, thinking to lubricate the joint and the gasket. Only one thing in my research have I found...there is a little metal pin just to one side of the marks on the lid that say "open" and "closed"...apparently this is some sort of lock pin that pushes up into the gasket from the pot base? and prevent the lid from being unscrewed at pressure...it is supposed to withdraw as the pot depressurizes? Slipping a feeler gauge in there won't make it move, either towards the lid or the pot. Looking at my old, broken lid and pot I see the remnants of a similar pin on the pot base, bent over to one side and apparently nonfunctional for a long time...and I had canned many a batch in that pot.
My last resort, which I will try when all else fails....my narrowest hacksaw blade will fit in there....I could possibly simply cut that pin off. It doesn't seem particularly essential, given that my other pot apparently functioned for years without it. Ideas?