A round-section elastomer ring compressed between flange faces, in a groove or on a centring ring. Viton (FKM) is the default for vacuum because it outgasses and permeates less than nitrile and takes bakes to about 150 °C; nitrile is cheaper for rough service, and perfluoroelastomers handle aggressive process chemistry. Seals go in clean and dry, or with at most a thin film of vacuum grease, and because they pass helium and water they limit elastomer-sealed systems to high vacuum.
Wipe the O-ring with a lint-free wipe, no grease, and check it for cuts before you clamp the lid.
Vacuum grease does not seal anything, it only lubricates; a thick layer traps dirt and outgasses, so a thin shine is the most a seal should carry.
Also heard as
- Viton
- FKM seal
- elastomer seal
Related terms
KF flange
Quick-release clamp flange with a centring ring and O-ring, the standard small fitting for rough and high vacuum.
ISO flange
Larger elastomer-sealed flange family, clamped with claws or bolted, used for pump and chamber ports.
Permeation
Gas passing through the solid walls or seals of a vacuum system by dissolving into and diffusing through them.
Hang-up
Helium that lingers in a leak detector or system after a big hit, holding the signal high and masking small leaks.