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).
Article detailing the extremely effective cleaning of a new oil filter by the Smith Accessory.
| Identifier | ExFiles\Box 135\3\ scan0110 | |
| Date | 1st January 1936 guessed | |
| A NEW OIL FILTER. Extremely Effective Cleaning by the New Smith Accessory. THERE is no doubt that an efficient oil filter may be an important factor in the life of an engine, particularly in regard to cylinder wear, because it is evident that if the oil in the sump is always pure and clean minimum damage must result. A filter is incorporated, of course, to remove suspended foreign matter, however finely divided. If a sample of oil be taken from the sump of an engine fitted with an oil filter, and this oil is found to be dirty looking and discoloured, then it may safely be assumed that the filter is not effective. An efficient filter should maintain clean oil, as new, throughout the working life of the filter; oil should only become dirty when the filter is clogged up. For some time Messrs. S. Smith and Sons (Motor Accessories), Ltd., have been experimenting with a type of filter which is claimed to be the most efficient filter so far discovered. It is stated that throughout its working life, which is approximately equivalent to 10,000 miles running, clean bright oil is maintained in the sump. The eventual clogging of the filter after this mileage is clearly indicated by the oil becoming discoloured, and may be easily seen by the eye on a polished chromium-plated dipstick; this indication being the warning that the filter requires replacing. The new filter is of the shunt type, i.e., a proportion only of the oil circulated by the pump passes through it. Thus when the filter clogs, or a stoppage occurs in the pipes, there is no immediate danger to the engine. It is usually fitted by teeing in to the oil gauge pipe as near the pump as possible, and running a return pipe to the sump at some convenient spot. The construction of the Smith oil filter is shown in Figs. 1 and 2. The filtering medium consists of specially prepared paper, two circular papers with central holes (see Fig. 3) being separated at the centre by tiny brass washers, one of which has a series of raised pips on one face to space it from the companion washer. The filtering papers are securely fastened together at the periphery (see Fig. 4), and the unit is threaded on to a hollow and perforated stem. A spacing washer (Fig. 5) is also fitted between each pocket. The filter pack is made up of a number of these units, and the whole sealed into a container carrying the inlet and outlet nozzles. Dirty oil enters the container and filters through the surface area of the double-faced units; the clean oil passes between the two papers, through the washer spacers to the central stem and back to the sump. 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 1.5 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 0.9 grammes of silica. In view of this analysis, it was decided to investigate the quantity of iron to be found in sump oils. Ten c.c. of sump oil was extracted and diluted heavily with filtered petrol. A horse-shoe magnet was embedded in wood to form a framework to hold a thin sheet of cellophane over the poles, and was then dipped into a porcelain dish holding the diluted oil. The contents were agitated gently for some considerable time, and then the magnet and cellophane were lifted out and washed in petrol. Finally when dried, the cellophane was removed from the magnet, and the resulting deposit of magnetic material photographed. Fig. 8 shows the quantity of magnetic material extracted from 10 c.c. of sump oil. Reading from left to right, they are: 10 h.p. car with no filter after 1,546 miles. 14 h.p. car with competitor's filter after 1,593 miles. 12 h.p. car with Smith filter after 1,542 miles. Digest of slime from filter, equivalent to 10 c.c. of sump oil. It will be seen that the oil from the sump with a Smith filter contains considerably less iron than with the competing filter, although the oil had been in for almost five times as long. A further quantity of dirty sump oil was collected and passed through the filter. Samples were taken before and after testing for acidity by shaking with hot water for 30 minutes, separating the water and titrating with N/100 sodium hydroxide solution in presence of methyl orange. The results showed that, considering the acidity as being H₂SO₄, the original dirty oil contained 0.0014 per cent., whereas after filtration the acidity was nil. It is claimed then that the Smith oil filter returns absolutely clean oil to the sump, even removing colloidal carbon. In this respect it is in advance of any other filter. During the early stages of use the foreign matter extracted from the oil helps to form a filter bed which is capable of extracting the very finest particles. Later, this bed increases in thickness until there is difficulty in getting oil to penetrate it. The flow through the filter then gradually falls, and the sump oil, in consequence, grows darker and darker. There is thus an obvious indication of when a change of filter is necessary. The removal of acidity by this filter, leading to less chemical corrosion, appears to be due to the fact that the acidity is present in conjunction with the water which inevitably enters the engine. For a long time oil technologists have been satisfied that oil retains its lubricating efficiency until the oil is completely used up. Discriminating engineers also agree that the useful life of an oil is not ended when it has been extensively used, although it may have collected a large quantity of impurities. While, however, the lubricating properties of an oil are not impaired, it cannot be denied that the presence of abrasive matter is bound to affect cylinder and bearing wear. Fig. 1. General arrangement of oil filter. A, Inlet. B, Outlet. C, Slot in outlet tube. D, Filter pad. E, Compression spring. F, Oil diffuser. Fig. 2. Internal parts of oil filter. Fig. 3. Filter unit. Fig. 4. Filter unit showing method of crimping edges together and central spacer. Fig. 5. Oil washer spacers. Fig. 6. Comparison between competitor on left and Smith filter on right. A, Before filtering. B, First time. C, Second time. D, Third time. E, Fourth time. F, Fifth time. G, 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, Sump. B, After 1,000 miles. C, After 2,000 miles. D, After 3,000 miles. E, After 4,000 miles. F, After 5,000 miles. G, After 6,000 miles. H, After 7,000 miles. Fig. 8. Magnetic material extracted from oil sump. Fig. 9. Sample of oil extracted from sump before filtration. 100 magnifications. Fig. 10. Impurities in oil from commercial lorry. 27 magnifications. Fig. 11. Oil after filtration. 200 magnifications. | ||