The CF (ConFlat) flange is the most widely used for high vacuum and UHV applications. Many gauges, instruments, accessories and feedthroughs are available on this flange system.
The seal mechanism is a knife-edge that is machined below the flange's flat surface. As the bolts of a flange-pair are tightened, the knife-edges make annular grooves on each side of a soft metal gasket. The extruded metal fills all the machining marks and surface defects in the flange, yielding a leak-tight seal. The CF seal operates from 760 torr (103 mbar) to <1 x 10-12 torr (<1.3 x 10-12 mbar), and within the temperature range -196° C to 450° C (depending on material). Flange sizes in North America are normally referenced by their outside diameter (O.D.). However, in Europe and much of Asia, the nominal internal diameter (nominal I.D.) of the largest tube that can be welded to a bored flange is usually referenced in their nomenclature.
ConFlat flanges are offered in four versions— all relating to the bolt holes.
Fixed flange: is a one piece design where the bolt-hole orientation is fixed with respect to that fitting.
Rotatable flange: is comprised of two parts, an inner weld ring and outer bolt ring. This enables the bolt ring to rotate about the inner weld ring.
Both Fixed and Rotatable flanges are available with your choice of clearance-holes or tapped holes.
Clearance-holes: Are through-holes that allow adequate clearance for bolts to go through both flanges and secured by nuts or plate nuts.
Tapped holes: Are imperial or metric threaded holes machined through the flange. This allows a clearance-hole flange to be connected without the need for nuts or plate nuts. Be aware of a components bolt hole orientation when selecting tapped flanges.