3-4 times per minutes is typical for Presto. Aim for the neighborhood of 3 and you'll be fine. Basically it's a steady regular movement, not overly vigorous.

It's better to use another rack and if you have a grill rack that fits and doesn't raise the level too high, that's fine. Otherwise, stores like Ace Hardware typically sell additional Presto racks in the canning supplies.

You don't need to add more water if your jars are double stacked. The pressure canner is a pressure chamber so as long as it's not running dry, stacked or not stacked is irrelevant to proper operation. I do add a bit more water with exceptionally long processing time (i.e. fish) but that's just me. A properly operated canner that's not running excessively hot isn't going to lose that much liquid.

For the same reason, stacked or not stacked, processing time and pressure remain the same.

The best source of information on canner operation is at the NCHFP site. Pay particular attention to vent times and wait times in the instructions. Do not follow recipes in the manual or use it for anything other than part numbers and basic instructions such as amount of water to use.

Carol

Here is a link that might be useful: NCHFP Using Pressure Canners

Thank you Carol for the fast and thorough answer.

I need to respectfully disagree with the 3-4 times per minute Carol mentioned above. While 3-4 times per minute is the recommended jiggle rate for Mirro and AA canners, Presto weights are machined a bit differently and need to jiggle slowly but steadily throughout the canning process. When at pressure it will move/hiss/jiggle almost continuously indicating 10.5 lbs of pressure. It is one of the advantages of the Presto - that lighter machining - since you don't have to count and time the jiggles.

For those of us who use multiple brands of canners we always have to remind ourselves which jiggle rate works for each brand of canner. :)

Dave

Thanks for the correction, Dave. I've not used the Presto for a while. You're right. I was thinking of the All-American.

And thank you, Pete, for the acknowledgement. We are happy to oblige.

Carol

Thanx Dave and Carol I do appreciate the help.