Kuruman: I used one of https://www.foodsaver.com/accessories-and-parts/jar-and-bottle-sealers/foodsaver-wide-mouth-jar-sealer/T03-0023-01P.html and single stage pump to evacuate the jar. Unfortunately, the vacuum lid adapter seems to seal almost immediately when vacuum is reversed and I don't see any way of releasing slowly.
digoff: Yes, this is actually a part of the project, another experiment. What I originally ended up doing was fitting #13 rubber stoppers to the jars (interestingly, I found out that there is a difference between the black #13 rubber stoppers and #13 tan... the tan ones end up getting sucked into the jar after a week or so, plus they are physically smaller than #13 black). The stoppers were center drilled and fitted with 1/4" pipe and plumbing valves. This has worked out well, but between the cost for these large stoppers, pipe pieces, and valves, it's expensive. The mason jars with their native lids evacuate and hold well up to 29" Hg and I was just looking for a simple way to release the vacuum slowly after a time. This would be cheap and easy to repeat. Right now, I have take a rather large cookie type jar and epoxied a valve into the lid. It's larger than the mason jar, so the mason will fit inside. Evacuate the larger jar until the mason lid releases, tilt the assembly so the mason lid falls away, then slowly release. I'm not sure this will work however. I have been able to somewhat more slowly release mason jar vacuum with careful strategic pressure applied from whatever opener I am using, but I'm not sure how repeatable and consistent this is.