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Basics 2: The Complete Dummy's Guide to Operation of a Typical Diffusion Pumped High Vacuum System

1. Introduction

This section is just for all those people who have never had anything to do with a vacuum system of any kind but need to use one. Diffusion pumped systems are still quite common, and used for all sorts of applications e.g. Vacuum Evaporators for making metal coatings. The diagram below is of a small bell jar system that we use for a variety of things here in the lab.

Since the introduction of the SI units, the unit "torr" is no longer to be used. Preferred units are now to be Pascal, it's derivative millibarr, and bar. Here are the Conversion Tables for Pressure Units from Edwards High Vacuum's web page for those who, like us, are still using older equipment calibrated in torr.

I have taken tongue in cheek "artistic license" and changed a few things in the drawing. The real-life glass belljar has been replaced by a metal vacuum chamber in the picture and the ion gauge is shown in the recommended inlet-down position to prevent problems with detritus dropping into the gauge. The diagram below is pictorial, there are a standard set of schematic symbols for vacuum systems which will also be included here eventually.