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).
Report analysing oil pump and filter design issues, specifically air trapping.
| Identifier | ExFiles\Box 149\2\ scan0110 | |
| Date | 17th August 1935 guessed | |
| -2- the lower half, but it will give a lead to future design. Evidently, when the sump was refilled, air became trapped inside the filter pot and suction pipe - the oil only reaching the level of the filter inlet port even when the sump oil level was above the top of the filter pot, and due to the "slip" inherent in the helical gear type pump, particularly at low speeds, the pump was not capable of withdrawing the air from the filter and suction pipe, and driving the oil remaining in the delivery pipe against the delivery restriction. This was shown by the fact that emptying the delivery pipe promoted priming, the delivery restriction being thus reduced. The essential differences between the "roof" type and the Bentley filters were that the filter area below the free surface of the oil with the former was vastly greater than with the latter, also in the "roof" filter the distance between the centre line of the outlet pipe, and the lowest point of the filter was reduced - this had the disadvantage with the existing type lower half that a higher minimum oil level was required. Preferably the filter outlet should be lower than the minimum oil level, and the suction pipe should fall very slightly towards the pump to avoid air lock in the pipe itself. These conditions would, however, be difficult to satisfy with the existing lower half. That the volume of air in the filter was not a decisive factor was shown by the fact that the volume of the "roof" type was twice that of the standard filter; incidentally the filter surface areas were similarly proportioned. Hs{Lord Ernest Hives - Chair}/W.Bell. | ||