Terminology Used in High Vacuum Components

If you use or specify high vacuum components, then you are probably very familiar with some or all of these terms: ANSI, CF, ISO, KF, LF, NW, QF ... they have become part of our vernacular; but what do they mean and how are they used?

Here is a quick overview with basic descriptions:

ANSI

ANSI: American National Standards Institute.  These are 150 pound series flanges commonly made to fit tubes ranging from 1.5” to 12” OD.  One flange will contain a machined o-ring groove and the other is smooth, and the seal is made by compressing the two flanges together with bolts.  ANSI took over this standard from ASA (American Steamfitters Association). ASA/ANSI flanges have been largely displaced by ISO-LF flanges. See below descriptions for ISO and LF.

CF

CF: ConFlat® which is a trade-mark of Varian Vacuum (now owned by Agilent). This is a flange system which employs two knife-edged surfaces that press on a metal gasket (usually copper or nickel plated copper) from opposing directions.  Used for ultra-high vacuum applications and also where the flange temperature will exceed the rating of elastomeric seals.
DN: Synonymous/interchangeable with KF or QF or NW.

KF

KF: Originally stood for “Klein Flansche (Flange)”; but now is usually thought of as “Kwik Flange” or “Klamp Flange,” and is interchangeable with QF and NW. This is the most commonly used flange type for vacuum applications down to as low as the 10-8 Torr scale for pipe sizes from 16mm to 50mm. An elastomeric o-ring is held in place by a centering ring, which rests on a step machined into each mating flange.  A KF (or “Kwik”) clamp then applies pressure on the chamfer machined into the outside of each flange, and the o-ring is compressed against the two flat inside surfaces of the flange.

ISO

ISO: International Standards Organization.  Most common vacuum hardware is built to ISO standards and thus different brands can be used interchangeably.  It is common to see references to “ISO-KF” and “ISO-LF”, and sometimes you may see an abbreviation to “ISO-40” or similar (which actually means "KF-40" or “QF-40” or “NW-40” in this example).

JIS

JIS: Japanese Industrial Standard.  A variation to the ISO standard system.

LF

LF: “Large Flange” system that employs a centering ring like the KF system, except rather than Kwik/quick clamps, it employs bolts and a single claw clamp or double claw clamps that grab onto a machined edge. Common sizes are 63mm to 250mm but LF can go up to 400mm.

NW

NW: Synonymous/interchangeable with KF or QF.

QF

QF: Quick Flange (most commonly used by ANCORP of Florida). Synonymous/interchangeable with KF or NW.

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