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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
Secondaryvacuum
Primaryvacuum
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 pictureof vacuum test setup
Test setup (2)
Sander Klous 24-11-2000
Measurements & Results• Conductance (H2O):
– 10-3 liter/sec without dedicated pump
– 10-5 liter/sec with dedicated pump
• Expected secondary vacuum pressure: 10-4 mbar
This would result in
10-9 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 pictureof 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 10-5 mbar
Valve 1Valve 2
Primary pump Turbo pump
Bellow
Secondaryvacuum
Primaryvacuum
Restriction
Conclusions
• All measurements indicate the gravity controlled valve can work
• For the correct dynamic pressure analysis a more realistic setup is required