A small flange family (ISO-KF, also called QF or NW) in which a hinged clamp squeezes two tapered flanges together around a metal centring ring carrying an elastomer O-ring. Sizes are named by nominal bore, with KF16, KF25, KF40 and KF50 the common ones. They go together by hand in seconds and seal to about 10⁻⁸ mbar, which makes them the default for forelines, gauges and lab plumbing, though the elastomer keeps them out of bakeable UHV.
Grab a KF25 clamp and a centering ring, we'll hang the Pirani off the foreline tee.
The O-ring on the centring ring does all the sealing, so a nicked, flattened or hair-covered ring is the first suspect when a KF joint leaks.
Also heard as
- KF
- ISO-KF
- QF
- NW
- quick flange
Related terms
O-ring
Elastomer ring with a round cross-section that seals demountable vacuum joints by being squeezed into place.
ISO flange
Larger elastomer-sealed flange family, clamped with claws or bolted, used for pump and chamber ports.
CF flange
All-metal flange that seals by biting knife edges into a soft copper gasket, the standard joint for UHV.
Foreline
Pipe that connects the exhaust of a high vacuum or booster pump to its backing pump.