From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
The comparative performance of oil filters, using paper spot tests to analyse oil cleanliness on the bench and during road tests.
| Identifier | ExFiles\Box 135\3\ scan0220 | |
| Date | 27th August 1937 guessed | |
| In testing the filter, to record the state of the oil at various stages during the tests, a method was devised by which a single drop was allowed to fall from a thin wire on to a fine-grade laboratory filter paper. The spot was carefully covered until entirely soaked into the paper. Under these conditions the solid material held in suspension in the oil is deposited in the centre of the spot, and the condition of the oil can readily be gauged by eye. The method had the advantage that it enabled both the actual record to be preserved for comparison with others, and also that it allowed of photographic reproduction. The Smith Filter, it is stated, produced clear, bright oil from thoroughly dirty sump oil. A comparison of performance with another type of filter was made on the bench. A quantity of dirty sump oil was collected from a number of cars, mixed thoroughly together and divided into two equal parts. The Smith Filter and the competing were then separately set to work on the two halves, sample spot records being taken each time the oil passed through the filters. Fig. 6 shows the results obtained. In the competing filter there was no appreciable improvement in the appearance of the oil even after six times through. The Smith, on the other hand, cleaned up the oil at the first operation, the oil delivered being clear and golden brown in colour. A number of filters were fitted to cars for road tests and the condition of the sump recorded at short intervals. Fig. 7 shows the condition of the sump oil at intervals of 1,000 miles on a 12 h.p. car fitted with a Smith Filter. The oil was not changed, but was topped up with 10 pints during the period of the tests. It will be noticed that the condition of the oil is no worse at 7,000 miles than after the first 1,000. Viewed on the dipstick it always looked perfectly new and bright. For purposes of comparison some records are included in the photograph of sump conditions on a car with a competing filter fitted and with no filter fitted at all. Analysis of the slime deposited on the papers of a filter which had concluded 7,000 miles on the road showed that a total oil-free residue of 122 grammes had been extracted from the oil. From this some 14.5 grammes of iron oxide were obtained by calcining, 1.7 grammes of oxides of other metals such as copper, tin, zinc and magnesium and 0.8 grammes of silica. Fig. 5. Separating washers, showing one plain and one with raised pips. Fig. 6. Comparison between competitor on left and Smith Filter on right. A.{Mr Adams} Before filtering. D.{John DeLooze - Company Secretary} Third time. B. First time. E.{Mr Elliott - Chief Engineer} Fourth time. C. Second time. F.{Mr Friese} Fifth time. G.{Mr Griffiths - Chief Accountant / Mr Gnapp} Sixth time through filter. Fig. 7. Comparison between 12 h.p. car with Smith's Filter on left, competitor's filter in centre, and without filter on right. A.{Mr Adams} On fitting. E.{Mr Elliott - Chief Engineer} After 4,000 miles. B. After 1,000 miles. F.{Mr Friese} After 5,000 miles. C. After 2,000 miles. G.{Mr Griffiths - Chief Accountant / Mr Gnapp} After 6,000 miles. D.{John DeLooze - Company Secretary} After 3,000 miles. H.{Arthur M. Hanbury - Head Complaints} After 7,000 miles. | ||