Most pressure canner brands (as of 2015) use rubber gaskets inside the lid cover, to help seal in pressure:
A pressure canner is a deep, heavy kettle that has a rack on the bottom for jars to stand on, a tight-fitting lid with a gasket, and a pressure gauge. The gasket keeps steam from leaking out around the cover. If the casket is worn, stretched, or hardened, replace it.” 1
The pressure canner brands that use a gasket include Presto, Mirro and Fagor.
Only one brand (as of 2015) does not, which is All-American: “It has a metal to metal seal, so there is no need to replace rubber gaskets.” 2 [A vintage brand, Kook Kwik, also used no gasket.]
NCHFP recommends changing rubber gaskets and rubber overpressure plugs just as a routine matter of course every 2 years 3 .
Some people say they replace their gaskets every five years (but don’t say how often they use the canner). Others say they wouldn’t push it that long: “As to a gasket lasting 6 years one of these days you will have a gasket blowout. They get brittle over time and are less stretchy. That’s when they blow.” 4 People say you’ll never know just how high you can jump until you’ve had an old, weak pressure canner gasket blow on you in mid-operation.
Some end users say they always keep a spare replacement set handy. The question usually eventually arises of how long a “spare gasket” in storage is good for. The University of Maine Extension seems to say five years: “Gaskets in unused lids work well for at least five years from their date of manufacture if stored in a cool, dry area.” 5
Presto, however, says you cannot store spare gaskets at all: “We do not recommend storing them, rather buy fresh each time you need to replace the rings. The rubber can and will deteriorate over time. ” 6 This could make having a gasket fail on you right at the start of a canning session quite problematic.
Let’s Preserve: Steps to Success in Home Canning. University of Maine Cooperative Extension. #4079. 2007. Page 3. ↩
Shelly at Presto Customer Service to healthycanning.com. 4/17/2015. Correspondence on file. ↩