Liquid-filled vacuum gauges

Before switching the pump on check that the traps are empty. Then with the 2-way tap closed and the 3-way tap open between the pump and the traps, but closed to the vent, turn the pump on. Next immerse the traps in Dewars filled with liquid nitrogen and check the vacuum by connecting a vacuum gauge to the 3-way tap. If the vacuum is satisfactory ([Pg.125]

If instead of mercury, a silicone oil is used as manometer liquid, the precision of reading increases tenfold. Thus the Laporte manometer uses such a filling for the range of 0.2 to 20 torr. A vacuum gauge working on the displacement principle [35] which serves for precision measurements between 0 and 10 torr exhibits an accuracy of 0.01 torr. Vacuum pump oO, purified paraffin and AmoU S cannot be recommended as manometer liquids since they absorb water and thus yield appreciable errors [36]. Following a suggestion of Bachmann, in the case of water some additives should be used which reduce the surface tension. 

More than 300 gallons (1.1 m ) of liquid nitrogen are held by the inner cooling jacket that has fill, vent, and drain lines, each protected as required with a pressure relief valve and rupture disk. Gauges showing the level and pressure of the liquid nitrogen are on the control panel. The outer jacket of insulation is protected from excess pressure and has an electronic vacuum gauge attached. 

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