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).
Investigation into petrol gumming, its causes, and the results of corrosion tests on fuel systems.
| Identifier | ExFiles\Box 103\5\ scan0169 | |
| Date | 1st February 1939 | |
| Extract from "Motor Service & Repairs" dated February 1939. AN INVESTIGATION INTO "PETROL GUMMING". There has been some concern lately among service managers and repairers at the effect on fuel systems of modern petrols, especially after a car has been stored for some time. A case we hard of is typical. The petrol outlet from the tank became blocked and occasionally the carburettor needle would stick. The tank was removed for thorough cleaning, but as it seemed to be corroded badly a new tank was installed. The top of the old one was cut off and the inside of the tank examined. The sides of the tank were covered with a thick brownish deposit, the copper and brass parts of the petrol gauge, etc. were bright green and some were pitted in places. The outlet was choked with a deposit formed by the petrol, gummy in nature. What is this gum? Briefly it is the produce of that part of petrol refined from the heavier oils by "cracking" and is formed only after a time. Fresh petrol is usually free from gum, but in time gum forms, especially if the spirit is kept in contact with metals. If there is any water present, the result is aggravated and corrosion sets in quickly. Corrosion Tests. We have seen the results of some lengthy tests carried out by Duckham's research laboratory who have investigated the whole question thoroughly. They wanted to find out if "Adcoids" had any effect on corrosion and sticking needles in carburettors. Many grades of petrol were tested in glass bottles. Some had water added and others the correct amount of "Adcoid". A spiral of copper wire was hung in each bottle and other metals were also tested. 156 samples were tested over eleven weeks, some in controlled daylight and others in darkness. The results showed that (1) all petrols (except two) in the presence of copper showed presence of gum; (2) where gum was formed it attacked and combined with the copper to form an insoluble compound; (3) in the presence of water the gum formation was worse; (4) those petrols which gave the heaviest gum formation also attacked the copper suspended in the vapour and caused corrosion; (5) "Adcoids" showed no increase in the tendency to form gum, but a slight decrease; (6) ethyl petrols also throw out an insoluble white compound. To test needles for sticking twelve carburettors were used and arranged so that petrol could trickle through each needle valve and the valves be closed every 10 minutes. Evaporation was | ||