UHV gate valve Readiness Review 20Sept2012

Notes/remarks/proposals 1) with standard configuration, seems hard to keep cold the actuator? ( VAT) 2) position of port 63CF : interference with oven/other: port tube side, diagonal, tbc (Gianni) 3) seal seat roughness 0.8 (Martin) 4) put the outgassing limits as contractual (Violette)

Questions #1 1. No minimum number of cycles is put in the specification. Why not putting a minimal number? Normally the catalogue number of cycles is quite high, cycles. The catalogue product should fulfill our needs 2. Do we have requirement on the speed of closure? This type of large gate valves arent very fast, normally s to change state. To reduce it significantly would normally need a new development of the valve itself. Even in this case we propose to select the catalogue product 3. When the valve is closed, its center will "see" the cryotrap. Could it be a problem like could the (small) deformation induced by the thermal gradient generate some leak? Small effects were evaluated (a few degree C, discussed also during TDR preparation). Normally gate valves are used in front of cryopumps, for instance also on the DT small cryotrap. A precise fem calculation could be maybe done

Questions #2 4. Do we have a record of how well the existing large valves performed like how many cycles have been performed? What was the measure leak rate? Does the viewport accident had an impact on the tightness of the valves (like dust prevent a proper closure of the valve). May be this kind of information could be added to strengthen the single source statement. For each valve we perform ed less than 100 cycles (tower ventings) ; after the viewport accident we vented the whole 3km tube just to inspect the valve, it was not damaged 5. (may be a question for Julien) I'm not sure to understand the second paragraph (and the consequences) of the conclusion of the document on stray light noise: VIR-0272A-12, namely "Nevertheless, the first rough estimation of the coupling coefficient due to what we labeled "path (2)" in fig.1 shows a surprisingly large value. This estimation rings a bell for the wide-angle scattering but more in-depth studies are needed to provide a more reliable estimation of the effects onto the AdV sensitivity". But figure 4 of this document indicate that even in high seismic noise conditions, the noise from the cryotrap baffle is well below the specification, meaning that we are safe. Is fig. 4 only for path 1 and not path "(2)"? Then what is the risk? In case, if some extra time could be useful for a further calculation, we could order just the 1st valve now (for the WE trap) and the 3 remaining ones months later.