Having trouble with that flat seal on your vintage canner?
The flat seals on the National Number 7 canner clones, such as the Presto 21-B are sometimes a royal pain to insert properly. They fit into a groove in the canner lids and if you are not careful, they will not get seated properly. Sometimes they can stretch and be even more difficult to fit.
After you’ve done it a few times, it doesn’t seem to be so bad, but the first time – you almost always think you have the wrong seal!
You push the seal into the groove from the inside out, working in small sections, constantly making sure that the seal doesn’t pop back out as you move on. Sometimes you have to start over. Sometimes you have to work your way around the lid a couple times. And, sometimes, the seal is just too old and stretched to fit any longer. When that happens you need to order a new seal.
Here is a brief video showing how I do it.