Vacuum gauges liquid

With the liquid nitrogen bath in place, the Teflon valve to the vacuum line is carefully opened and the solvent container is evacuated for 10-30 min. Because it is advantageous to go through several FPT cycles, step 2 should not be unnecessarily prolonged for any one cycle. During the first cycle, the vacuum gauge should be closed to the vacuum line. 

There are two basic ways for a vacuum gauge to read a vacuum direct and indirect. For example, say that on one side of a wall you have a known pressure, and on the other side of the wall you have an unknown pressure. If you know that a certain amount of deflection implies a specific level of vacuum, and you can measure the current wall deflection, you can then determine the pressure directly. This process is used with mechanical or liquid types of vacuum gauges. On the other hand, if you know that a given gas will display certain physical characteristics due to external stimuli at various pressures, and you have the equipment to record and interpret those characteristics, you can infer the pressure from these indirect measurements. This indirect method is how thermocouple and ion gauges operate. 

The liquid gauge family is identified simply as vacuum gauges that have some liquid (usually mercury or a low-vapor-pressure diffusion pump oil) directly in contact with the vacuum. The amount of liquid movement is directly proportional to the force exerted on it, and the (measured) amount of movement is read as the vacuum. Because mercury has traditionally been used for vacuum measurement, the term millimeters of mercury is commonly used even with nonliquid gauges. 

On the other hand, a liquid trap is essential between any liquid vacuum gauge and the manifold itself. The simplest accident can cause hours of needless delay as the vacuum line is cleaned out. Normally a simple splash trap is sufficient (see Sec. 7.4.6). Vacuum systems that go below 1CT5 torr should consider to have a cold trap placed between their liquid vacuum gauges and vacuum systems. This placement will keep vapors from contaminating either side of the system. 

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]

Figure 1. Schematic Diagram of the Dual-Sampling Vapor-Liquid Equilibrium Apparatus. Components are labeled as follows 6PG, Gas pressure generator GRP, Gas recirculation punqp HZ, Heated zone LPG, Liquid pressure generator LRP, Liquid recirculation pump P, Pressure gauge RV, High pressure sanqpling valve SPV, Sapphire pressure vessel VG, Vacuum gauge. Hatchmarks on the lines in the saxtqpling section of the apparatus indicate where heaters have been wrapped on them. The path of vapor saxtqples is indicated by light arrows and the dark arrow shows the path of liquid sanples.

The apparatus is completed by a receiver for the bottoms (J) and a transition piece (K) with a connection to the vacuum gauge. For deodorization work or for the processing of mixtures with a small proportion of low-boiling material the transition piece (K) is replaced by the deodorization piece (O). Through the lateral inlet the vapour of a low-boiling product can be passed counter to the falling liquid film in order to enhance the flow toward the condenser and to prevent recondensation of the distillate. A siphon prevents condensation in the bottoms receiver. 

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. 

When handling a liquid which gives rise to a corrosive or flammable vapour which may damage the vacuum pump or constitute a hazard, residual vacuum may be used. In this procedure, when the vacuum gauge reaches a steady reading, valve 1 is closed before admitting liquid to the suck-up line. 

The apparatus used to determine the pure component isotherms is illustrated in Fig. 1. This system consists simply of the adsorption cell, a constant temperature bath, a source of adsorbate (i.e., CH4), and a high-vacuum oil manometer to measure the adsorption pressure, TTie reference pressure of the manometer is monitored with a thermocouple vacuum gauge. Adsorption temperatures of 76 and 88.5 K were obtained with atmospheric baths of liquid N2 and respectively the other temperatures as measured with a copper-con-... 

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. 

In directly measuring vacuum gauges, the elastic restoring force of a spring element (diaphragm) or of gravitation (liquid column) is used for pressure measurement. 

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