VAC - Vacuum Flange Types and Sizes

Created by Kathleen Patrick, Modified on Tue, 10 Sep at 1:39 PM by Kathleen Patrick

General Information:

No, NW, KF (from Klein Flansche) and QF are the same types of vacuum flange systems. KF is the more popular European term, while NW is more popular in North American. QF in reference to Quick Flange, is descriptive of the type flange system. Most standard NW/KF style quick release vacuum connections are made from a high quality grade 304 stainless steel. Stainless steel is a cleaner, stronger and more durable alternative to aluminium. For specific applications, some vacuum components are also available in aluminium.

The NW/KF system refers to the bore dimensions.

NW/KF Size	External Diameter (A)	Internal Diameter, Metric (B)	Internal Diameter, Imperial (B)
NW/KF10	30mm	14mm	12.7mm (½")
NW/KF16	30mm	20mm	19.05mm (¾")
NW/KF25	40mm	28mm	25.4mm (1")
NW/KF40	55mm	45mm	38.1mm (1½")
NW/KF50	75mm	57mm	50.8mm (2")

C = length of flange can vary

Vacuum Connection Parts and Fittings

Vacuum clamps, O‐rings, centring rings, blanking plates, hose adapters are widely used in vacuum systems and low‐voltage pipe systems, such as electronic, food machinery, the petrochemical industry, and medicine machinery. Most vacuum fittings come with plastic protective caps which help protect the NW/KF flanges from scratches and dust.

A typical KF or NW assembly consists of two identical flanges, a centre-ring and a clamp with a fastener that allows for frequent connection and disconnection without tools. A vacuum seal is created by uniform application of pressure by the clamp on 15° surface of the flange. When the clamp is tightened the flange surfaces compress the o-ring (held in place by the centre-ring) to generate a seal.

Hinged clamp assemblies like the one above are most commonly used for making KF-flange vacuum seal connections. Assembly is simplified by the 360° rotatable flanges ad self-centring feature of the centring-ring.

Applications for vacuum systems are as varied as the imagination and include use for:

Roughing and foreline plumbing for vacuum systems
Small systems
Systems demanding frequents changes or cleaning
Experimental systems in research laboratories
Teaching laboratories

ISO fittings (ISO‐K / ISO LF)

ISO fittings are joined by a centring ring and an elastomer o‐ring.

ISO Clamp

"The ISO large flanges come in two varieties. The ISO‐K (or ISO LF) flanges are joined with double claw clamps which clamp to a circular groove on the tubing side of the flange. The ISO‐F (or ISO LFB) flanges have holes for attaching the two flanges with bolts. Two tubes with ISO‐K and ISO‐F flanges can be joined together by clamping the ISO‐K side with single claw clamps which are then bolted to the holes on the ISO‐F side." ‐ Wikipedia

ISO large flanges are available in sizes from 63 to 500mm nominal tube diameter.

ISO standard size	Tube Diameter
DN63LF	63.5mm
DN100LF	102mm
DN160LF	160mm
DN200LF	200mm
DN250LF	254mm
DN320LF	316mm
DN400LF	400mm
DN500LF	500mm

Conflat fittings (CF / ISO‐F)

Conflat (CF) fittings use a copper gasket and knife‐edge flange to achieve an ultrahigh vacuum seal.

"Each face of the two mating CF flanges has a knife edge which cuts into the softer metal gasket, providing an extremely leak‐tight, metal‐to‐metal seal. Deformation of the metal gasket fills small defects in the flange..." ‐ Wikipedia