RECONSTRUCTION OF OIL-VAPOR HIGH-VACUUM PUMPS *)

The entry of oil from high-vacuum high-speed oil-vapor pumps into the vessel being evacuated is a source of serious difficulties in working with such pumps. The oil, or, still worse, the products of its decomposition, reach sensitive surfaces and alter their physical and/or chemical properties. The latter is especially true in vacuum systems containing beams of electrons or ions. In this case the processes of oil decomposition proceed considerably more actively.

The authors of the article being reviewed observed, in particular, the deposition of oil-decomposition products on the cooled anticathode of X-ray tubes during special studies of soft X-rays. During continuous operation of the pump for a week, up to 1 cm³ of oil was deposited. In order to reduce oil deposition, the authors undertook a reconstruction of the pump. Its essence is clear from the figure. Here the dashed line shows the former position of the nozzle. After reconstruction the nozzle was shifted downward and its shape was correspondingly changed. In particular, the nozzle was made strongly divergent. In addition, the inner tube of the pump was covered by troughs,¹ secured to the tube by means of glass insulators. (In the limiting case the troughs may be water-cooled.)

Fig. 1.

Both of these measures were intended to accelerate the arrival of vapor molecules at the condensing surfaces. A certain (in the authors’ opinion, secondary) role was played by the fact that octoil S was used in the reconstructed pump, whereas silicone oil (DC 703) had previously been used.

All these measures led to an almost complete absence of traces of oil in the vacuum system, although the pump continued to operate under the same conditions as before. The authors emphasize that the reconstruction is simple and feasible for the most diverse pumps available to an investigator.

[V. V. Fedorov]