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?
The hacksaw trick sounds like it would work but before going to that stage, have you tried removing the gauge or the over pressure valve to make sure there is no pressure inside which may be keeping that pin engaged?
+1 check pressure, per Gerry. So easy to do something that will look really silly down the line... Do the simple stuff first.
Pour boiling water around the pin area, then ice water, then boiling water, then ice water. Then tap (gently with a brass hammer or a steel hammer on top of a couple sheets of paper) likely spots around that pin to encourage it to behave properly.
That failing, if the thing will go into a freezer, leave it over night, then, immediately, pour boiling water over just the lid like you did before .
While waiting for it to freeze, find a "strap wrench". These consist of a specially shaped handle with a 3/4" - 1" x 12" to 18" strap attached; often people use powdered resin on the strap just baseball pitchers used to do to give improved grip. A chain wrench uses the same idea, but instead of a strap it has a chain - might not want that because it will chew up the aluminum a bit. It may be hard to find a strap wrench with a long enough strap. Find out how long it needs to be to fit around the edge of the lid, then get some narrow webbing and sew it onto the end of the strap the wrench came with to give you a long enough strap.
There are two ways to use it: Apply the wrench to the lid and hold the pot, or apply the wrench to the pot and hold the lid. In the case of wrench-on-pot, you may want to take a thin (1/8-3/16) piece of wood and place it under the fulcrum point where the handle contacts the pot. There is a LOT of pressure at that point and it'd be nice to not puncture the pot. Putting a small piece of sheet metal under that point would also help. The box stores sell sheet metal as "welding material" and if you're really into it, you can get some 1/8" plate, cut a small piece and then form it into a curve a little tighter than the outside of the pot (hammer it over some kind of form) to spread that load even more.
If you working alone, it will be (has been?) hard to hold the pot really strongly while cranking on the lid - or vise versa. Working on a wood bench that you can screw into can help here. Screw wood blocks into the bench to position either the pot of the lid and catch protrusions to hold it while you twist. That assumes, of course, that the work bench is "nailed down".
Finally, depending on the damage to the original lid, it's possible it could be welded. There is a break in the skill level of welders. Most "farmyard" welders (like me) don't make it past steel and into the skill level of good aluminum fabrication. So if looking into this, look at what work the person has done on aluminum before deciding.
Breaking an old faithful tool is a real bummer. Best luck.
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