I took apart the 4.5" CF Gate Valve from Alan Rice in hopes of cleaning it effectively since it was sitting out and exposed on a shelf and is over 40 years old. It was visually dusty. I took apart the top screws (probably 1/4-20) and pulled out the sealing flange and the machinery to make the gate valve open and close. The parts are horribly discolored. As a sanity check, I was able to put everything back together and I then put it away in a bag. There is no one-time-use gasket sealing the system, but instead a silver colored square ring that is 3.5" x 1.5" on the outside, a horizontal thickness of ~0.095", and a vertical thickness of 0.033" (1/32"?). There didn't appear to be a knife edge. There is a separate set of screws by the handle of the gate valve that come off but there wasn't any gasket there.