VACUUM TECHNOLOGY-compiled by Benson .O Oderah. Vacuum is any enclosure whose pressure is less than atmospheric pressure. (760mmHg) APPLICATIONS OF VACUUM TECHNOLOGY 1. Electron microscopy 2. Sugar refilling 3. Vacuum filtration 4. Production of electric lamps/vacuum tubes 5. Vacuum cleaning 6. Semi conductors processing 7. Radio therapy and surgery 8. Freeze drying 9. Coating of glass Terminologies 1. Mean free path-difference between one point to another in a vacuum system. 2. Throughput- pressure *volume / time 3. Conductance-reciprocal of resistance 4. Digass-_removal of any gas inside a pump. 5. Critical baking pressure-pressure which can be tolerated in diffusion pump to start pumping. 6. Leak route-amount of gas which enters or appears to enter the vessel in unit time. 7. Pump matching-ability of pump to work together with pressure from other pumps 8. Pumping speed-through put( pv / t )/ volume / time Types of vacuum systems 1. Static vacuum system-system pumps down, remove them and finally seal them. I.e. thermoflask and radio waves 2. Dynamic vacuum system-involves continuous evacuation. I.e. research institutions and industrial purposes Equipment’s for evacuation/rotary vav e pumps A) ROTARY OIL SEALED PUMP. Four stages in one cycle Levels of vacuums 1. Low vacuum 760-25 torr 2. Rough vacuum 25-1 torr 3. High vacuum 1*10 -3 - 10 -6 torr 4. Very high vacuum 10 -6 - 10 -9 torr 5. Ultra high vacuum less than 10 -9 torr Vacuum pumps Two general classes 1. Gas transfer-physical removal of matter i.e. mechanical and diffusion pumps
2. Adsorption – entrapment of matter i.e. sublimation and ion pumps. Rotary oil sealed pump-10 -3 torr (high vacuum) Rotary + diffusion pump-10 -2 - 10 -6 torr Note . Rotary pump create vacuum, roughing the system and backing up diffusion pump. Other classification of pumps 1. Roughing pumps i.e. rotary oil sealed pumps 2. Backing pumps i.e. diffusion pumps 3. Holding pumps Rotary oil sealed pumps/mechanical pumps are used for; 1. Production of medium, high vacuum on their own 2. Roughing the system down to a pressure at which diffusion pump can start pumping
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- Fall '14