McLeod gauge cleaning

Be aware that the old oil from a pump (and any solvent used to clean out the old oil) more than likely contains any toxic materials that may have come from the vacuum system. For example, if the system had a McLeod gauge, it is likely that the old oil is contaminated with mercury. The amount of contamination concentration determines how the oil or solvent can be disposed of. Unfortunately, because of the possibility that specific EPA-established concentration levels will change before you read this book, no disposal procedures are provided. Therefore, contact the EPA, or local regulatory agencies, to verify the various toxicity levels and the proper disposal procedures for materials of those levels. 

The McLeod gauge uses mercury, which can be a nuisance because the gauge is difficult to clean and may be illegal in some areas. In addition, backstreamed mercury can sometimes affect your work. 

Invariably, the mercury within a McLeod gauge will get dirty. The telltale evidence is when the mercury does not cleanly run down the glass tubing and/or you see a film on the surface of the mercury. Traps are the best way to avoid this problem. 

A McLeod gauge must be removed from a system when it is being cleaned. This removal probably will involve the talents of a glassblower. The mercury should be carefully poured out of the gauge and sent to a mercury distiller for cleaning. The grease should be removed by an appropriate solvent. Silicon grease should never... 

It can be very difficult to get liquid into various parts of a McLeod gauge because of the closed capillary tubing. One solution to this problem is to use a vacuum cleaning setup as shown in Fig. 7.46. A Teflon stopcock is used because it requires no grease. 

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