Vacuum-Component Assembly: Tips and Procedures

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UHV Vacuum Components

CF Conflat Flange
QF/KF Quick Flange Tee
CF to KF adapter


The flange on the left is called a CF or Conflat flange. Bolts, nuts and copper gaskets are used to attached components.

The flange in the middle is called a QF (or KF) Quick Flange. O-rings and clamps are used to attach components.

The rightmost component is a CF-to-KF adapter.


Making CF attachments

When making CF attachments bolts, nuts, washers and copper gaskets are used.
copper gaskets
used CF copper gasket

Observe the indented ring on the used copper gasket. It is caused by the CF flange knife edge and provides the UHV (Ultra High Vacuum) seal.

CF tech 4.gif

Clean all components in a mild detergent solution in the sonicator. Rinse the sonicated components in distilled water then methanol. Dry components with (e.g.) the heat gun. Inspect the CF knife edges for damage (see photos below). Damaged knife edges like those shown below will leak and limit vacuums to the mtorr-torr level.

bad knife edge close-up
bad knife edge close-up


Align CF parts. Be careful not to bang parts together and damage the knife edges (easily done). Do not attempt to mate misaligned parts by just tightening the bolts.

Using clean gloves, place a (fresh/new) copper gasket against the knife edge seal of one of two standard CF flanges, preferably the flange most likely to hold and support the gasket from falling. With the gasket in place arrange mating flange with the desired bolt hole orientation. If flanges are fitted with leak-test grooves, these should be aligned. With flanges aligned, insert proper size bolt and hand tighten. Washers are typically used on the nut side of the fastener assembly. Repeat this procedure with the remaining bolts.

After hand tightening all bolts, support bolt and turn nut using two closed-end box wrenches. The tightening process must be done gradually in 1/8 to 1/4 turn increments in an alternating crisscross pattern. Continue this incremental tightening until the desired torque ratings have been achieved. Tightening bolts in this fashion will insure a reliable seal with even gasket compression and deformation.

UHV component examples:

CF right angle valve
CF bellows


CF Tee
CF 4-way cross
CF 6-way cross

Example of assembled UHV system

Uhv system.jpg