The angled sealing ridge inside the face of a CF flange, recessed below the flange surface so it is partly protected. On assembly it plastically deforms the copper gasket and forms a metal-to-metal seal. A nick or radial scratch across the edge, from a dropped flange or a screwdriver, will leak, so flanges are stored with caps on and never set face-down; a shallow ding can be recut on a lathe, while a deep one means a new part.
Don't set that flange face-down on the bench, ding the knife edge and we're scrapping a whole nipple.
Also heard as
- knife-edge seal
- sealing edge
Related terms
CF flange
All-metal flange that seals by biting knife edges into a soft copper gasket, the standard joint for UHV.
Copper gasket
Flat ring of soft oxygen-free copper crushed between two CF knife edges to make a metal vacuum seal.
Blank
Solid flange with no hole, used to seal an unused port or to test a pump on its own.