* * * INSIGHT * * *

Keeping the Oil Clean

By

Thomas A. Jennings, Ph.D.

In a previous INSIGHT (Vol. 5 No. 7) I considered the basic functions of the vacuum pump and some of its inherent problems. This latter INSIGHT showed that the typical oil seal vacuum pump uses a liberal amount of oil for lubrication. The two basic problems associated with this type of pump is that decomposition of the oil that occurs from the normal operation of the pump or the condensation of condensable gases are a prime source for backstreaming and excessive wear and tear on the pump. In the case of backstreaming there is the real potential of contamination of the product by the low molecular weight hydrocarbon vapors; whereas, the presence of condensable vapors (excess indication of oil in the pump) can lead to corrosion and wear of the pump and a loss in pumping speed. A loss in pumping speed can lead to higher chamber pressures and have a major impact on the control of the primary drying process. While a properly designed drying process along with periodic changing of the pump oil will help eliminate such problems none-the-less it is a time consuming process and high grade vacuum pump fluid is not inexpensive but it can become even harder to justify the discarding of such oil when it only shows a slight discoloration. It is the purpose of this INSIGHT to propose a means in which the light hydrocarbons and condensable gases can be removed from the oil so that the useful life of the oil is extended but also undesirable condensable vapors are removed without having to resort to use of the ballast valve which will cause an increase in oil temperature and a reduced pumping speed.

Volume 5 Number 11                                                                               November 2002

4 Pages          2 References           2 Figures

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