Working ranges of vacuum pumps

Fig. 2.25. Working range of vacuum pumps and multistage pumpsets.

Speciai working range of vacuum pumps I I Normal working range of vacuum pumps Figure 5.2 Common operating pressure ranges of mechanical vacuum pumps. 

Vacuum pumps, either singly or, more usually, as part of a pumping system, create and maintain the conditions appropriate to a required process. Each of the types of vacuum pump available has a characteristic working range in which it is effective. Outside that range, shortcomings in performance become apparent. 

In the high-vacuum range, fractionating vapour jet pumps are employed as diffusion pumps after oil seal vacuum pumps. These vapour jet diffusion pumps are equipped with especially constmcted nozzles with a diffusion slot. The working range of this type only starts in medium high vacuum and leads to high vacuum or molecular distillation. 

Irving Langmuir s contributions to the advancement of catalysis research were many and varied, ranging from important theoretical concepts to the invention of vacuum pumps and gauges which facilitated experiment. In this paper, we review this work and attempt to place it in the historical context of the science of the time and the laboratory in which he worked, and describe how Langmuir took full advantage of his opportunities to act as both an insider and an outsider in the field of catalysis. 

Investigations of vacuum pumps with fluidic optimised working openings and free of dead space have shown that the named pressure range can also be covered without variable pressure slots. 

The pressure range is the pressure difference of the maximum pressure and the minimum pressure in which a vacuum pump can work efficiently. It is necessary to combine the different types of pumps together to generate high vacuum pressure. 

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. 

Roots efficiencies of about 70% or more can be achieved if k0 > 20 and Sth/Sback < io. Although such values for the staging ratio are satisfactory in the medium vacuum range, lower values are desirable if there are large variations in operating pressures or if the Roots pump is working where k0 is small. 

---