My turbomolecular pump (Leybold) and vacuum chamber (Pfeiffer) have difference in knife edge diameter of ~0.5 mm. This results in a noticeable camber in the used gasket and the pressure not going below 10-9 Torr. Leak detected with He.
I learned from Kurt J. Lesker that flanges up to 10'' OD are highly standardized, but not 12'' and higher.
What could I do to make a good seal? Use annealed gasket? Machine a thicker one?
Dear Pavlo,
I cannot imagine that the leak is really due to the mismatch of the knife edge diameters. The ductility of the Cu gasket is to my opinion sufficient enough.
Do you have repeated the sealing by some other (fresh) gaskets and all the time the leak shows up?
You have to tighten the screws of the flange very gently successively one after one in a lot of circles around the flange with slightly increasing torque for each circle. Please use a torque wrench.
Alternatively to the Cu gaskets you may try silver or even gold plated ones.
Please ensure that the knife edges are free from any scratch(es) and being free from dust and no pores should show up at the surface(s) of the gasket. You could have got a bad one.
Thank you, Gerhard Martens . I have just replaced the gasket, and there seems to be no leak. The flange location is not torque wrench friendly. So I had to go by feel and consistent small turning angle for each bolt.
Dear Pavlo, I made similar experience in the past - you may check if there are providers that do offer thicker gaskets - the cheap ones are often quite thin and may not result in a leakage free connection of the flanges. But it seems as if your problem is solved :-) Best regards, Dirk
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