Vacuum tests Problem description Valve presentation Test setup Measurements & Results Conclusions

Problem description Separated primary and secondary vacuum to obtain good ring vacuum Thin foil required because of multiple scattering Intrinsically safe solution is desired Secondary vacuum Primary vacuum Electronics, cables, etc. Thin foil

Valve presentation Valves that react to differential pressure Electric/Pneumatic, but… –Fail-safe solution required Proposal: Gravity controlled valve

Test setup Leak rate during normal operation (with/without pump) Preliminary: –Dynamic response to sudden pressure changes (leaks) –System behavior during pump down Removed picture of vacuum test setup

Test setup (2) Sander Klous

Measurements & Results Conductance (H 2 O): –10 -3 liter/sec without dedicated pump –10 -5 liter/sec with dedicated pump Expected secondary vacuum pressure: mbar This would result in mbar l/s leak-rate Pumping slots

Measurements & Results (2) Dynamic response –Maximum differential pressure over the valve is 6 mbar Measurement is dominated by the bellow configuration (see picture) –More realistic measurements are required with faster gauges Removed picture of tandem (gravity- controlled) valves

Measurements & Results(3) Pump down time –Conductance between primary and secondary vacuum: Bellows (L = 1 m, d = 20 mm) –Maximum pressures in range of the gauges: 500 mbar, calibrated with a baratron. 3 hours to around 1 mbar (  p = 9 mbar at 500 mbar) 3 hours to mbar Valve 1 Valve 2 Primary pumpTurbo pump Bellow Secondary vacuum Primary vacuum Restriction

Conclusions All measurements indicate the gravity controlled valve can work For the correct dynamic pressure analysis a more realistic setup is required