Technical Notes & Dimensions

QF Flanges

KJLC's QF Flanges are simple and flexible O-ring vacuum coupling equal to the flanges known as KF (or Klein Flange) by the International Standards Organization, and KJLC's QF flanges are also compatible for vacuum sealing with KF flanges from European manufacturers. An assembly consists of two identical ("sexless") flanges, a clamp, and a centering ring to align the flanges and to prevent the O-ring from collapsing. The thumbscrew clamp typical for QF flanges requires no tools for assembly. The system is ideal for small diameter tubing that needs frequent reassembly. QF fittings work in rough or foreline vacuum plumbing and simple HV (10^-8 torr) chambers. The elastomeric O-ring limits the connection's temperature range and ultimate vacuum.

The simple, one piece clamping arrangement used for QF flanges up to a tube diameter of 2 inches (50mm), changes for larger diameters to a system of multiple clamps or nuts/bolts. These larger diameters are called 'ISO' or 'Large ISO.' The sealing mechanism using an O-ring and centering ring remains substantially the same for QF and ISO. It is possible to extend the simple clamping procedure used for QF to diameters exceeding 50mm; and in countries other than the US, particularly Japan, this is done. There is almost not reason why this clamping mechanism cannot be extended above 50mm since the joint, under vacuum, has the considerable force due to atmospheric pressure preventing the two halves of the flange from separating.

Stainless steel fittings withstand adverse temperature and corrosion conditions, while aluminum or brass fittings work for more general applications.

Greases & O-Rings

Some experts advise users to grease the O-ring before assembly. However, leak-free joints depend as much on the absence of dust or lint particles on the O-ring and imperfection on the flange surfaces as on the presence or absence of grease. The choice between "to grease or not to grease" probably relates to how oil-free the user wishes the system to be. Greases, in general, have very low vapor pressures, but any measurable vapor pressure means the grease will (very slowly) migrate from the O-ring to other surfaces.

Low cost Buna-N O-rings are compatible with most chemicals found in vacuum applications; and can withstand temperatures to 100ºC (we recommend 80ºC). Fluorocarbon O-rings withstand 170 to 200ºC (we recommend 150ºC) and a greater range of chemicals. Silicone O-rings are rated usable at 200ºC for long periods; but silicone hardens and sticks firmly to the flange surfaces. High terp options include Kalrez and Clemraz (300ºC).

QF weld fittings (stainless steel) fit standard (USA) stainless steel tubing sizes (1/2, 3/4, 1, 1 1/2, and 2 inches); QF solder and braze fittings (brass) are compatible with standard (USA) copper tubing sizes (1/2, 3/4, 1, 1 1/8, 1 5/8 and 2 1/8 inches).

QF Flange Dimensions