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 in10-9 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