Absolute Vacuum Connections

It all depends on the grade, or quality of a vacuum you need. For single torr values one can easily get away with neoprene O rings and gaskets. But to get to an ultra high vacuum level of 10^-9 torr (UHV) then only metal gaskets nominally of copper must be used. This is because along with the roughing pumps, turbo pumps and ion pumps used to maintain this low pressure with the out gassing and slow leak cavity traps that will likely occur, the chamber will likely have to be baked under vacuum to accelerate the process. After cooling the pressure will hopefully drop to the desired UHV level. Oh, don't forget that you'll need a helium leak check before baking to assure that not even the tiny molecule of helium can seep in.

Just look at lamp industry or even transmitter manufacturing industry. New lamps are mounted on an indexing table and after processing etc, it is sealed and taken out. Nearly one lamp gets produced every 10 seconds or less. Now the lamp has to have vacuum of nearly 2 microns. So it is a quick connect and disconnect system. Look up quick couplers for vacuum from google. I have downloaded a few for my use.

Hi,

if you are working with KF-flanges and Viton O-rings then it is a necessity to rework the flange-surfaces until no longer any scratch is visible and polish slightly to have best tightness.

If this is not good enough then do a double O-ring with in-between evacuating by a rough pump (10-3 mbar). Or have some cooling for the O-ring area as leakage through the ring material is very dependent on temperature.

If you need below 10-6mbar and don't want to cool or use double O-ring-seals then switch to Conflat-flanges or similar with OF-Cu or aluminum seals (expensive).

There is also an old version with silver-seals deforming from circular to more triangular cross section at tightening. I prefer these as I can make the silver rings myself for next to nothing and do not have to use expensive flanges and seal rings. Silver rings brazed to near circular shape from (ideally 999Ag but really 825 or 800 is working too). Silver rings can be used 3 to 10 times as the triangular groove is only on one side and the other is flat and the ring is turned over after a use so newly deformed at tightening.

I use diameter 0.7mm wire for up to 100mm diameter flanges and 1 to 2 mm for bigger size.

After tightening and pump-down take a look if tightness is at the desired level: close all valves and measure the pressure rise with time.

Be sure that nobody will touch the interior or chamber or tubing with naked fingers, ban any materials that are not outgassed, ban any brass, non-SS-steel, use only outgassing approved plastics (there is a list from NASA and ESA) or do your own outgassing test by heating the plastics to 150°C and measuring the pressure rise in a completely sealed chamber.

Vacuum may be a source of frustration!

Have success

RHABE