I've fixed rotary vac pumps by pulling the lid, driving out the remnants of the stock check valve, tapping the lid to 1/8 NPT making sure to chamfer the edges so the vanes don't catch and installing one of these check valves. Be sure that when you tap the lid you don't tap so far that the check valve will protrude past the lid. I then used a 1/2" barb fitting (I cut it off a fitting I had on hand), tapped it to 1/8"NPT and attached it to the check valve. It works perfectly and is an upgrade from the stock piece in being much more robust.
You need to sell these for real!
When I figure out how to I will copy your post and make it an FAQ sticky since it seems all on here have been having vac pump issues all last year.
Done.
It has its own post in the FAQ, and a link to that FAQ post in the FAQ Quick Guide, under miscellaneous.
I meant without quoting it. I wanted it to look new and fresh
