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Vacuum (Beam splitter)
Boschi, Gherardini, Menzione, Ruggi, Vacuum - 17:33 Thursday 02 July 2020 (49007) Print this report
follow-up of the IVC repair activity on BS tower

The tower BS is now closed and the evacuation has been started.

 

In the past days we have carried out various activities on the IVC with the aim of locating and mitigating its leaking defect:

- The leakage has been localized in correspondence of the bottom joint, where the IVC chamber rests on the flat viton seal (by visual localization +  He-test in 'sniffer mode' with He via V82), see fig.1.

- The mitigation/repair has been attempted by adding a second seal (a viton cord of diameter 3 mm) for a lenght of about 1.5 m, or 1/3 of the seal circumference (see sketch in fig.2).The seal is held in position by slight pulling the cord itself + a few spacers.

- in addition, a viton o-ring of the IVC (the one of the base of the pipe at bellows level) was found not well positioned and it was redone

Notes:

- figs.3,4 pictures of the BS IVC , of the concerned area with the viton cord not yet in place

- the IVC has not been opened nor raised

 

The 'amended IVC leak' will be tested again once under vacuum in the next few days.

 

Other recordings: leak test activity performed in the preceding days on BS tower under vacuum:

Testing for external leak presence = no significant external leaks detected
- He-test upper rings joints: leak rate < 1E-8 mbar.l/s
- He-test lower flanges: leak rate < 1E-8 mbar.l/s

Images attached to this report
Comments to this report:
Francescon, Gherardini, Macchia, Pasqualetti, Sentenac - 0:04 Friday 10 July 2020 (49044) Print this report

After the recent repair/mitigation attempt on the BS IVC, the BS tower has been put under vacuum and then tested in order to re-estimate the residual ‘leaking defect’ through the IVC.

The test has been done by injecting the He gas inside the tower upper part (via Vc2, CL 6.6E-7 nom.) and measuring the He flux reaching the lower part (and then the upper too) by the usual Leak Detector.

The IVC ‘leaking' defect is estimated around  ≈ 3 x the expected figure (while before the intervention the estimate was > 10 x ).

A significant reduction has been achieved.

 

Here some recordings:

Before the repair: LD_old lower =7.2E-8 A.U.

After the repair run I: LD_old lower =1.1E-8 A.U.

After the repair run II: LD_new lower =1.4E-8 A.U.

test pressure 1E-5 / 1E-6 mbar; 400/547Hz

PR tower: LD_old lower = 0.5E-8 A.U. (for comparison)

Additional note: we have rechecked the leak tightness of the tower upper rings (opened/closed for the intervention). No leaks found above > 5E-8 mbar.l/s.

 

In conclusion: the defect has been localized and a significant mitigation has been accomplished. We consider the intervention completed for the moment.

Also, we shall prepare for a more reliable a repair,  to be implemented when needed or convenient for the general plan (normally a new suitable seal replacing the present one found leaking, suitably shaped. It will require to raise the IVC by some mm during the installation).

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