LATEST DEVELOPMENTS ON VALVE SEAT-SEAL ASSEMBLY

The Helicoflex(R) metallic seal initially designed for static assembli es is presently used as a valve primary seal for specific applications where the elastomeric seal commonly used in such a configuration is t otally unsuitable owing to low resistance to radiation and high temper ature, and incompatibility with ultrahigh vacuum conditions. The hydro gen injection quick valves of the JET fusion reactor, as well as the a luminium ultrahigh vacuum valves of the TRISTAN accelerator already op erate using this technology over a rather narrow range of working cond itions. In order to widen the field of applications and establish the basic principles of the sealing function applied to a valve seat-seal assembly, tests were carried out in the Sealing Techniques Laboratory of the French Atomic Energy Commission (CEA). The seat configuration a nd seal holding device have been reconsidered. Seals have been tested using different grades of sealing lining material, i.e. successively a luminium, silver and copper. In this respect, such an assembly configu ration was found to be in full compliance with the requirements of the new types of valve, those which are being considered for applications where ultrahigh vacuum is combined with a leak rate requirement of 10 (-10) Pa m(3) s(-1) and a high bake-out temperature.