Hi! Thanks for your comment and question. Actually, all of the vents in the backround of that video are Hoffman 1As. They represent about 100 years of 1A vent design changes. And I am still coming up with even more variations to this day! The Hoffman vacuum vent I believe you desire are designated 2A and look very similar to the older style 1As. It is a VERY slow vent. Check out my YouTube channel where I discuss the 1A. I hope to make a vid on the vacuum vent at some point...
Sorry, yes I’M thinking of the Hoffman 2, non adjustable very slow venting designed for vapor vacuum. I think it still have a 76 main vent on there. It was so green and covered in rust I can barely read the numbers. Had ot cut it off. Bet it’s original or from maybe the 40’s.
Just checked the vent again. Shows Patent March 1915. SO not original. Was a replacement then.
Do you know of a good, cheap 1/8” NPT check valve that I could use inline ahead of an air vent? Challenge is that it need a have cracking pressure of 0.5 oz or less. Basically a silicone diaphragm/flapper setup.