Flanges are used as a flexible joint between a vacuum chamber and any pumps or components you might want to attach to the chamber. In the simplest case, this might be a blind flange to close an unused tube on the chamber. The most common flanges are so-called conflat flanges, which come in different standard sizes.

Sealing between two flanges is achieved by putting a gasket in between them. Copper gaskets and silver-plated copper gaskets are common and viton gaskets can be used as a temporary solution if you do not need to bake. The actual sealing proceeds by a knife-edges on the mating flanges as they are pressed together. A blind flange with and without gasket is seen in the picture below.


The number of holes for screws depends on the size of the flange. Flanges can be bought in different steel qualities, with tapped holes or through holes, rotatable or fixed.

When putting two flanges together with a copper gasket in between, make first sure that the knife edges and the gasket are really clean. Then check that the gasket really sits at the right position before tightening the screws. Finally, tighten the screws gradually, either going around in circles around the flange or cross-wise from opposing sides. For very big flanges or sensitive objects (viewports) it can be advisable to use a torque wrench. In the case of large viewports the problem is that you can put a lot of stress on the glass-steel joint when you tighten the screws on one side too hard. 

Always be careful not to damage the knife-edges of the flanges, especially of those which are welded to your vacuum chamber! Sometimes it can be hard to get copper gaskets out again, especially after many bakes. If you have this problem, there are special gasket removal tools. Using a screwdriver is usually dangerous and not a good idea.


index               home