Cleaning a McLeod Gauge

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. 

When the stopcock shown in Fig. 7.46 is turned to one position, a vacuum will be created in the item to be cleaned. Rotating the stopcock 180° will allow the cleaning or rinsing solution to be drawn into the piece. Then by rotating the stopcock one more time while holding the item in a draining position, the liquid can be removed into a filter flask. 

Silicone stopcock grease requires cleaning and replacement every month or two whether the stopcock is used or not (see page 198). 

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