These KF-25 centering ring vacuum fittings are supplied with chemical resistant Kalrez 6375 O-ring material and are designed for use with standards ISO-KF 25 (NW-25) vacuum fittings. The O-ring material, Kalrez 6375, is a Perfluoroelastomer (FFKM) well known for its excellent chemical resistance when handling amines, acids, bases, and other aggressive chemicals while also having excellent resistance to heat (525°F/275°C) and steam. Kalrez 6375 is considered to have the widest possible operating range of chemicals and operational temperatures applicable for a variety of applications which makes it a popular choice for use in high-technology vacuum areas.

These KF-25 centering rings are commonly used to build fore-line vacuum piping inside chemical process systems, semiconductor, oil, and gas connections. They are often called quick flange fittings because they are quick to assemble. A circumferential clamp and centering ring form the vacuum seal between the connecting flanges (please see top right figure - click to enlarge). The centering ring contains a rubber elastomer O-ring, chemical resistant Kalrez 6375 material. The standard sizes for quick flange fittings are KF-10, KF-16, KF-25, KF-40, and KF-50 with flange sizes NW-10, NW-16, NW-25, NW-40, and NW-50, respectively. Kalrez is a Perfluoroelastomer (FFKM) and registered trademark of DuPont Performance Elastomers.