Pumps lining

Solvent-divert system. Used in conjunction with an interface, it permits temporary interruption of the flow from a chromatograph to a mass spectrometer by briefly opening a valve to a pumping line. Thus effluent present at a high concentration (usually solvent) does not enter the mass spectrometer ion source. 

Diffusion Pump System. After the pump line and trap have been shut off, a large valve is opened slowly enough that the mass flow of gas from the chamber through the valve into the od-diffusion pump system does not dismpt the top jet of the diffusion pump (DP) (Fig. 4). When the Hquid nitrogen is replenished after the trap has been operated for some time, release of previously trapped gas must be avoided. The so-caded ionization-gauge response pips at the start of the Hquid-nitrogen replenishment are an indication of trap ineffectiveness. 

When a gas is removed from a container through a tube, the type of gas flow depends on pressure. In the low vacuum range, the gas flow is controlled by the collisions among molecules (viscous flow). If some molecules are removed from a region (by a pump), other molecules will refdl the empty region. In this situation, the diameter of the pumping line... 

Often the flow in a pumping line is neither molecular nor viscous. 

The complications of windows can be avoided by substituting small apertures above and below the sample to restrict the diffusion of gas molecules while allowing penetration of the electron beam. Typically, pairs of apertures are added above and below the sample, with differential pumping lines attached between them. In the early in situ experimentation, an ECELL system (69) could be inserted inside the EM column vacuum between the objective lens pole pieces. 

Methanol can be pumped in existing gas stations, but since the fluid is corrosive the pumps, lines, and tanks would have to be made of stainless steel. If there is a demand, the costs would likely be handled by private investors. 

Instead of rotary pumps, large water jet, steam ejector, or water ring pumps can be used. For batch evacuation, and the production of hydrocarbon-free fore vacuum for sputter-ion pumps, adsorption pumps (see Section 2.1.8.1) are suitable. If the use of oil-sealed rotary vane pumps cannot be avoided, basically two-stage rotary vane pumps should be used. The small amount of oil vapor that backstreams out of the Inlet ports of these pumps can be almost completely removed by a sorption trap (see Section 2.1.4) Inserted In the pumping line. 

Since the main pumping lines are usually constructed from tubing with an internal diameter (i.d.) of ca. 2.5 cm, viscous flow predominates until the pressure is reduced to ca. 10" Torr, when the high vacuum pump is usually switched into the system. 

Electrically controlled connections to the inert gas supply and the vacuum pump line which are capable of maintaining any desirable pressure inside the box. This control system should include pedal switches to allow operation by foot while the hands are engaged inside the glove box. 

Apparatus. The experiments were performed in a vacuum system consisting of a preparation chamber and an analysis chamber separated by a gate valve. The preparation chamber was pumped by a 150 1/s turbo pump to a base pressure of lxl0 mbar. A quadrupole residual gas analyzer (RGA) was connected to the pumping line of the chamber. It did not have a direct line-of-sight to the specimen. Gases could be admitted to the chamber as desired through a variable leak valve. In the preparation chamber, the specimen could be mounted in a heatable support where it could be irradiated with an electron gun. A transfer device allowed the specimen to be moved to the analysis chamber without exposure to air. 

Procedure. The apparatus should be assembled by coimecting the necessary pressure gauges, filling lines, and pumping lines see Fig. 3. Evacuate each chamber by closing clamp or stopcock C and stopcocks A2 and B2 and opening stopcocks 1 and Bl. Then close stopcocks A1 and Bl and test for leaks in either chamber by waiting approximately 15 min to see if the manometers indicate any increase in pressure. The rate of increase in pressure should not exceed 5 Torr/h. 

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