Traps for Pumps

All pumps should be protected from materials within the system, the system should be protected from all pump oils, and a diffusion pump (if any) should be 

Any water or hydrocarbon solvents left from previous operations should be removed from traps before beginning any new vacuum operations. Otherwise, any materials in a trap when first beginning operation will be drawn directly into the pumps, which is what the traps are trying to prevent. Having no material in the traps to begin with removes this possibility. 

Cold traps must be used if mercury is used in your system (such as manometers, diffusion pumps, bubblers, or McLeod gauges) and if your mechanical pump has cast aluminum parts. Mercury will amalgamate with aluminum and destroy a pump. Even if your mechanical pump does not have aluminum parts, the mercury may form a reservoir in the bottom of the mechanical pump, which may cause a noticeable decrease in pumping speed and effectiveness. Aside from a cold trap between the McLeod gauge and the system, place a film of low vapor pressure oil in the McLeod gauge storage bulb. This oil will limit the amount of mercury vapor entering the system that makes its way to the mechanical pump. In addition, an oil layer should be placed on the mercury surface in bubblers and other mercury-filled components. 

When first starting up a vacuum system, let the pumps evacuate the system (if starting up the system for the first time) or the traps (if they have been vented to the atmosphere) for a few minutes before setting the traps into liquid nitrogen. Otherwise you are likely to condense oxygen in the traps and create a potentially dangerous situation when the pumps are turned off (see Sec. 7.4.3). 

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Medium-resolution absorption spectrometer emission spectrometer with red-sensitive photomultiplier or CCD detector laser excitation source such as listed in Table 1 (or medium pressure mercury arc such as described in earlier editions of this text) neon calibration lamp and power supply (available from, e.g.. Oriel Corp., Stratford, CT) reagent-grade iodine 100-mm glass cell with Teflon stoppers for absorption studies heating tape with controlling Variac 50-mm cell for emission studies vacuum system, preferably with a diffusion pump and cold trap, for pumping down emission cell. 

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