Vacuum system, maintenance

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. 

The role, design, and maintenance of creepproof barriers in traps, especially those in oil DPs, remain to be fully explored. In general, uncracked oil from a DP is completely inhibited from creeping by a surface temperature of <223 K. On the other hand, a cold trap, to perform effectively in an ordinary vacuum system, must be <173 K because of the vapor pressure of water, and <78 K because of the vapor pressure of CO2. For ultracontroUed vacuum environments, LN temperature or lower is required. CO2 accumulation on the trap surface must be less than one monolayer. The effectiveness of a LN trap can be observed by the absence of pressure pips on an ionization gauge when LN is replenished in the reservoir. 

The equipment required for the construction, maintenance and use of a high vacuum system comprises ... 

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. 

As can be seen in Fig. 6.5, the Dewar is a double-wall glass container which is coated on the inside with a silver deposit. During manufacturing, after the Dewar is silvered, it is attached to a vacuum system and evacuated to about 10 6 torr before being tipped off (see Sec. 8.2) to maintain the vacuum on the inside. The Dewar achieves its temperature maintenance capabilities because of three different principles ... 

What can be limited is the backstreaming of condensable vapors. This can be achieved through the effective use of baffles, traps, and using good vacuum system design. The simple resolution for backstreaming of condensable vapors from standard pumps is proper system design and proper maintenance of the traps. 

Efficient high-vacuum pumps generally do not operate well near atmospheric pressure. Thus the vacuum system must have a mechanical vacuum pump to evacuate the system to a pressure where the high-vacuum pumps are effective. Mechanical pumps require routine maintenance, such as ballasting and replacing the pump oil. The diffusion pump is the least expensive and most reliable high-vacuum pump. Turbomolecular pumps and cryopumps are also used on mass analyzers. The high-vacuum pumps also require... 

Ciba Speciality Chemicals realised that their existing vacuum system was excessively wasteful in terms of lost product, maintenance requirements and disposal of contaminated lubricating oil (GC235). 

The MS-200 has a membrane inlet concentrator which allows a wide range of gases to be identified and measured from the low parts per billion range up to percentage levels. No operator maintenance or specialist knowledge is required for the vacuum system. The system also uses El ionisation and a TOP mass analyser. The mass range is up to 1000 amu and sensitivity is <5ppb (for benzene). 

In general, most reactions involving hazardous or toxic vapor phase precursors are operated at reduced pressure from a safety perspective. Additionally, the enhancement of kinetic steps often occurs by operating at reduced pressure. As indicated in the individual chapters of this book, many reaction schemes involve operation at low pressure, and, therefore, care must be taken with the vacuum system, its maintenance, and the exhaust of a reaction co-product stream. For specific applications of low pressure operation, the reader should consult the appropriate chapter on the material of interest. 

Whenever possible, more rapid turnaround time, the absence of load locks, the reduced maintenance cost associated with the avoidance of vacuum systems, and the ease of incorporation into continuous processing systems, all combine to make atmospheric pressure chemical vapor deposition an attractive technique. In general, removal of reaction co-products is accomplished by utilization of a large excess of carrier gas (typically argon or nitrogen). Additionally, it may be noted that the thermal oxidation... 

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