Helicoflex seal test
The Helicoflex seals which are used at the top lids of our 5 vacuum tanks are custom made and thus considerably expensive (approx. 3kCHF pp.). It is recommended to use this sort of seals only once, because they experience a considerable deformation and cannot be placed at the exact same position.
However, we tried it out to reuse the seal of YIN. During tightening of the screws we found that the
specified torque of 25 Nm was not enough to bring the machined precision faces of the top lid into contact with the reference face of the tank. It was necessary to apply about 70 Nm. Using this torque we
experienced several failing screws and nuts. It was very helpful to replace the standard stainless steel screws (A4 specification) with brand screws and silver plated nuts, made by Bulten, Sweden. Bulten screws and silver plated nuts are normally used by the SLS vacuum group because of their better sliding performance during tightening.
The higher torque helped to bring top lid and tank closer together but the top lid seal had several small leaks. It was necessary to mount a new seal to reach UHV conditions (24.1.2000).
All tanks which remain to be delivered will be equipped with Bulten screws and nuts.
