Vacuum systems

Vacuum exhaust connections for the through shuttles are provided at the face of the reactor for the convenience of experimenters in setting up their equipment. These are part of the experimental services normally provided at all beam hole facilities. 

Prior to delivery of a shuttle to the reactor, the pneumatic shuttle system is under a slight vacuum since the. solenoid valves at the ends of the shuttle tube are open to the reactor cooling-air exhaust system. The sequence of operations that take place d li ing delivery of a shuttle can be better understood by reference to Fig. A9.B. 

Shuttles prepared for delivery to the reactor are introduced into the system at the loading terminal. After the cover is secured, the operator presses a switch which automatically closes all valves in the vacuum lines and 

If the shuttle is to be sent to the laboratory, the shuttle transfer tube is rotated to the laboratory position during the time interval in which the shuttle is irradiated. Rotation of the shuttle transfer tube automatically closes the solenoid valve that has been supplying the air to propel and cool the shuttle and, after a fraction of a second delay, opens the solenoid valve in the air-supply line that by-passes the shuttle transfer unit. This now provides the air necessary to cool the shuttle and the shock absorber. 

1 Pressare Drop. When the shuttle is positioned at the center of the reactor by the shock absorber, an approximate pressure drop of 38 Ib/sq in, is required to force 0.04 lb of air per second through the shuttle tube. This.is equivalent to 31.8 cfm of air at 70°F and atmospheric pressure of 14.7 Ib/sq in. 

It is the responsibility of the utilities manager to follow the procedure. The quality assurance manager is responsible for SOP compliance 

Three vacuum systems are commonly used in modern aseptic manufacturing facilities (1) house vacuum systems, (2) vacuum systems dedicated to lyophilization equipment, and (3) vacuum systems dedicated to autoclaves or other sterilization equipment. 

As-built drawings of the vacuum system within the plant should be available. The vacuum system should be installed in accordance with the set specifications. Records about maintenance repairs and modifications should be filed. 

Check and document that the pumps conform to purchase specifications. Connect the pumps to the required utilities and document that the utilities are correct. Tighten flanges and mounts. Fill pumps with oil (if required). Check shock mountings and remove shipping restraints. Calibrate. Check and document all critical process instrumentation. 

The following tests should be executed with disconnected vacuum-consuming equipment 

To attain high reaction speeds as well as high water vapour flow speeds in the chamber and condenser, the partial pressure of permanent gases must be lowered to the partial pressure of the water vapour. In order to avoid hindering condensation of the water vapour in the condenser, the share of permanent gases should be low (usually around 1 X 10 mbar). 

Another criterion when dimensioning a vacuum system lies in the demand that evacuating the system from 1000 down to 10 mbar should be attained in less than 30 min. 

The attainable ultimate pressure of such a pump set, for example during secondary drying, should not lie lower than the water vapour partial pressure of the condenser when loaded with ice since, otherwise, there is the danger of resublimation of the ice in the condenser or evaporation in the direction of the vacuum pumps. The result would be an increased water content in the pumps and this would lead to inefficient operation. 

A condenser temperature of approximately —70°C corresponds to a water vapour pressure of 2.6 X 10 mbar 

The required ultimate pressure of the pump set is thus approximately 3 X 10 mbar. 

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Clearly, the lower the ionization energy with respect to the work function, the greater is the proportion of ions to neutrals produced and the more sensitive the method. For this reason, the filaments used in analyses are those whose work functions provide the best yields of ions. The evaporated neutrals are lost to the vacuum system. With continued evaporation of ions and neutrals, eventually no more material remains on the filament and the ion current falls to zero. 

Ions and neutral molecules headed for skimmer orifice, drawn mainly by the vacuum system... 

Vacuum system. Components associated with lowering the pressure within a mass spectrometer. A vacuum system includes not only the various pumping components but also valves, gauges, and associated electronic or other control devices the chamber in which ions are formed and detected and the vacuum envelope. 

Direct-inlet probe. A shaft or tube having a sample holder at one end that is inserted into the vacuum system of a mass spectrometer through a vacuum lock to place the sample near to, at the entrance of, or within the ion source. The sample is vaporized by heat from the ion source, by heat applied from an external source, or by exposure to ion or atom bombardment. Direct-inlet probe, direct-introduction probe, and direct-insertion probe are synonymous terms. The use of DIP as an abbreviation for these terms is not recommended. 

Moving-belt (ribbon or wire) interface. An interface that continuously applies all, or a part of, the effluent from a liquid chromatograph to a belt (ribbon or wire) that passes through two or more orifices, with differential pumping into the mass spectrometer s vacuum system. Heat is applied to remove the solvent and to evaporate the solute into the ion source. 

The inactivity of pure anhydrous Lewis acid haUdes in Friedel-Crafts polymerisation of olefins was first demonstrated in 1936 (203) it was found that pure, dry aluminum chloride does not react with ethylene. Subsequentiy it was shown (204) that boron ttifluoride alone does not catalyse the polymerisation of isobutylene when kept absolutely dry in a vacuum system. However, polymers form upon admission of traces of water. The active catalyst is boron ttifluoride hydrate, BF H20, ie, a conjugate protic acid H" (BF20H) . 

The helium leak detector is a common laboratory device for locating minute leaks in vacuum systems and other gas-tight devices. It is attached to the vacuum system under test a helium stream is played on the suspected leak and any leakage gas is passed into a mass spectrometer focused for the helium-4 peak. The lack of nearby mass peaks simplifies the spectrometer design the low atmospheric background of helium yields high sensitivity helium s inertness ensures safety and its high diffusivity and low adsorption make for fast response. 

Titanium hydride is used as a source for Ti powder, alloys, and coatings as a getter in vacuum systems and electronic tubes as a sealer of metals and as a hydrogen source. 

Metallization layers are generally deposited either by CVD or by physical vapor deposition methods such as evaporation (qv) or sputtering. In recent years sputter deposition has become the predominant technique for aluminum metallization. Energetic ions are used to bombard a target such as soHd aluminum to release atoms that subsequentiy condense on the desired substrate surface. The quaUty of the deposited layers depends on the cleanliness and efficiency of the vacuum systems used in the process. The mass deposited per unit area can be calculated using the cosine law of deposition ... 

Space needs to be provided for the auxiliaries, including the lube oil and seal systems, lube oil cooler, intercoolers, and pulsation dampeners. A control panel or console is usually provided as part of the local console. This panel contains instmments that provide the necessary information for start-up and shutdown, and should also include warning and trouble lights. Access must be provided for motor repair and ultimate replacement needs to be considered. If a steam turbine is used, a surface condenser is probably required with a vacuum system to increase the efficiency. AH these additional systems need to be considered in the layout and spacing. In addition, room for pulsation dampeners required between stages has to be included. Aftercoolers may also be required with knockout dmms. Reference 8 describes the requirements of compressor layouts and provides many useful piping hints. 

Optimum Design of Pumping, Compression, and Vacuum Systems... 

Because of the low efficiency of steam-ejector vacuum systems, there is a range of vacuum above 13 kPa (100 mm Hg) where mechanical vacuum pumps are usually more economical. The capital cost of the vacuum pump goes up roughly as (suction volume) or (l/P). This means that as pressure falls, the capital cost of the vacuum pump rises more swiftly than the energy cost of the steam ejector, which iacreases as (1 /P). Usually below 1.3 kPa (10 mm Hg), the steam ejector is more cost-effective. 

Other factors that favor the choice of the steam ejector are the presence of process materials that can form soflds or require high alloy materials of constmction. Factors that favor the vacuum pump are credits for pollution abatement and high cost steam. The mechanical systems require more maintenance and some form of backup vacuum system, but these can be designed with adequate reflabiUty. 

Separate all noncondensables before feeding to WEE or SPE unit (even a small amount of noncondensables overloads vacuum system, especially at ultrahigh vacuum ranges) most low molecular weight compounds do not condense at cooling water temperatures under high vacuum. 

Components must be stable at boiling point of mixture (probably mn under vacuum) vacuum lower than 7—13 kPa (50—100 torr) may requite specialised (scraped-film) crystalliser, more compHcated vacuum system. 

If mnning under vacuum, separate noncondensables before feeding to crystalliser (excessive noncondensables ovedoad vacuum system or lead to oversized design). 

Nonmolecular species, including radiant quanta, electrons, holes, and phonons, may interact with the molecular environment. In some cases, the electronic environment (3), in a film for example, may be improved by doping with impurities (4). Contamination by undesirable species must at the same time be limited. In general, depending primarily on temperature, molecular transport occurs in and between phases (5), but it is unlikely that the concentration ratios of molecular species is uniform from one phase to another or that, within one phase, all partial concentrations or their ratios are uniform. Molecular concentrations and species that are anathema in one appHcation may be tolerable or even desirable in another. Toxic and other types of dangerous gases are handled or generated in vacuum systems. Safety procedures have been discussed (6,7). 

A vacuum system can be constmcted that includes a solar panel, ie, a leak-tight, instmmented vessel having a hole through which a gas vacuum pump operates. An approximate steady-state base pressure is estabUshed without test parts. It is assumed that the vessel with the test parts can be pumped down to the base pressure. The chamber is said to have an altitude potential corresponding to the height from the surface of the earth where the gas concentration is estimated to have the same approximate value as the base pressure of the clean, dry, and empty vacuum vessel. 

Ultrasound frequencies can be introduced into the walls of the vacuum system. If a source of ultrasound is placed on the wall of an ultrahigh vacuum system, a large hydrogen peak is observed. Related phenomena, presumably from frictional effects, are observed if the side of a vacuum system is tapped with a hammer a desorption peak can be seen. Mechanical scraping of one part on another also produces desorption. 

Molecules arrive at the surfaces of traps and baffles by volume flow and surface creep. Molecules are trapped in vacuum systems by binding with energies much greater than kT of the surface, where k is Boltzmann s constant and Tthe absolute temperature, or by lowering the temperature of the surface in such a way that kT is less than the heat of physisorption of a molecular species on a surface. 

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