DLab Prosthesis: One Way Valve Issues

I have been using a vacuum to creating the jamming effect in the modified vacuum bags. The problem is that the vacuum that is strong enough to pull air out is also strong enough to lift the value up so that the coffee can also be pulled out. This is a problem because the casting system slowly deteriorates and the vacuum will not maintain the shape of the coffee if the coffee is gone. I have modified a value with a cloth covering.

This is the inside of the testing vacuum, obviously the 1 way value has let coffee through

This is the front of the value with the cloth backing

this is the back of the value

Also, the plastic isn't very strong or tear resistant. I got nylon patches (so they just stick, with no heat) and have started to cover the shells with them.