DEVELOPMENT OF AN ALUMINUM-ALLOY VALVE FOR AN EXTREMELY HIGH-VACUUM SYSTEM

An aluminum alloy manually operated right angle valve of bellows type, having conflat flanges (CF) of 1.33 in. in outer diameter, was developed for aluminum alloy extremely high vacuum (XHV) systems. To reduce the total outgassing from the inner surface of the valve, all inner surfaces were finished in an oxygen and argon atmosphere (EX process) with the exception of the bellows whose outer surface was chemically polished. To obtain an extremely low leak rate adequate for the XHV system, a sealing principle of a combination of a mirror-finished surface with a TiC hard coating and an aluminum Helicoflex seal was applied to the seat and other sealing parts of the valve. Using a new method for measuring the leak rate with a new type quadrupole residual gas analyzer, it was confirmed that the magnitude of the leak rate of the valve was of the order of 10 - ‘14Torr l/s. The operating life was more than 5000 opening/closing cycles, compared with a few hundred operations in the conventional valves. In addition, the cycle life of a new aluminum alloy gasket with a mirror-finished surface was tested and it required half the force to seal as compared to the original Helicoflex seal. © 1990, American Vacuum Society. All rights reserved.