Rough Pumpdown from Atmospheric Pressure
Objective: Experimentally obtain the pumpdown curve in a rough vacuum regime.
Reference: Modules 1, 3, 8 and 9
Varian Vacuum Trainer
Student must wear latex gloves when handling vacuum components.
1. Insure that the system has achieved equilibrium at atmospheric pressure. All valves should be closed. Remove the bell jar and let stand for at least 15 minutes.
2. Visually inspect the base plate and gasket for cleanliness. If the gasket needs cleaning, wipe with alcohol. Dry thoroughly with a lint-free cloth. Lubricate with a thin film of vacuum grease.
3. Place the bell jar and shield on the baseplate.
4. Close all valves.
5. Plug in the vacuum trainer.
6. Turn the Mechanical Pump Switch to the ON position. Turn the Turbo Pump Switch to the OFF position.
7. Select the roughing gauge on the controller (TC1, Channel 1).
8. Check to make sure that the gauge is reading atmospheric pressure ( 7.6 on +2 scale). Note: The thermocouple gauge is not accurate above 1 Torr.
9. Press START on the Turbo Controller Panel.
10. Allow the pump to run for at least one minute. Then open the roughing valve in one continuous motion. Start the stopwatch as you begin opening the valve.
11. Record the pressure at 30 second intervals for the first 5 minutes. Then record the pressure at 1 minute intervals for the next 5 minutes and at 2 minute intervals until completion. (Minimum length of time for the experiment is 20 minutes).
12. Plot pressure versus time on semilog graph paper. Seven cycle x 70 division semilog paper is recommended.
13. Compare to the results to the benchmark experiment.