How to Make and Maintain a Vacuum

Aristotle s statement nature abhors a vacuum means that even if you are successful in creating a vacuum, your ability to maintain that vacuum can require an equal, if not greater, amount of work. When creating a vacuum, you must establish your needs, define (and understand) your conditions, consult with authorities before you make purchases, and understand (and accept) any compromises. 

We often euphemistically refer to creating a vacuum as emptying a container of its contents. But, what does empty mean We already stated that it is impossible to make a container void of contents, so what do we need to do to empty a container  

say that you take a glass, pour out the contents, dry the walls, and bake out the glass so it is truly empty. The question is, Will it now remain empty until water is poured back in As far as vacuum science is concerned, no. As soon as the glass is exposed to the atmosphere at room temperature, the walls will resaturate with water vapor, and the glass will no longer be empty. To maintain a glass as empty, it must be isolated from the atmosphere. Otherwise you must repeat the drying process. 

What typically happens with a glass vacuum system is that first a mechanical pump removes a great deal of the loose, or free, gas particles. Then, greater vacuum is achieved with the combination of a diffusion pump (or similarly fastpumping unit) and traps that remove or bind up the various vapors within the system (for example, oil, mercury, and water). The only way a system can achieve a vacuum lower than 10 6 to 10 7 torr is if the pump can remove water vapor faster than the water vapor can leave the walls. Most diffusion pumping systems cannot achieve this goal, but even if they could, there is such a substantial amount of water vapor within the glass that, unless the walls are baked, a better vacuum cannot be obtained. 

Aside from adsorbed gases, there are potential leaks in any vacuum system that must be dealt with or a viable vacuum cannot be created. Leaks and leak detection are dealt with in Sec. 7.6. 

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