I'm done with valve/zipper bags, m'self. Got a case of these with tin ties.
The valves are only necessary on sealed bags; I believe it's a presumption -- not a valid inference or deduction -- that they are important to avoid oxygen migration into a bag. An unsealed bag with a labyrinthine series of folds is at least as good, and less expensive.
Or so the oracle tells me. 
Stockbag's price on the tin ties are pretty expensive.
Try Papermart next time.........
Argh.
I was pwned.
Thanks for the tip.
I'm done with valve/zipper bags, m'self. Got a case of these with tin ties.
The valves are only necessary on sealed bags; I believe it's a presumption -- not a valid inference or deduction -- that they are important to avoid oxygen migration into a bag. An unsealed bag with a labyrinthine series of folds is at least as good, and less expensive.
Or so the oracle tells me.
The valves are for physical protection of a pretty full bag with fresh beans in it.
Fill the bag with air, roll it up and put on the tie. When you slowly step on the bag, which gives first, the bag or the rolled/tin tied top?
It is also handy to be able to squeeze excess air out of the bag after resealing it, something that is a little tougher to do on your labyrinthine valve without encountering a ahhh.... a sudden pressure discontinuity.
I shall retain some valved zippered bags for my clumsier or non-deft customers.
But seriously, is that the purpose of the valves? Because if so, the prevalent meme is quite at variance . . .
