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).
Letter to W.A. Robotham explaining a potential cause for a fuel gauge inaccuracy issue related to air locking.
| Identifier | ExFiles\Box 61\3\ scan0213 | |
| Date | 9th July 1931 | |
| M W.A.Robotham, Esq., Date 9.7.31. Page 2 will let you know the result of our efforts next week. I shall also await with interest an appointment to let Holt observe the behaviour of the gauges on the track at Brooklands next week. It has occurred to me that there may be an explanation for the loss of the top half gallon on the gauge in the case of the car we inspected at your works yesterday. First, it is our experience that it is almost impossible to get an absolutely full reading gauge by the "blow-up" method which we use in the vent pipe of the single line installation. It may therefore be that the gauge which we corrected by this means was not giving an absolutely its full reading. I believe it was found on calibrating this tank that the top gallon actually extended into the filler and tank vent, thus air locking the top and forward portion of the tank to get in the 20 gallons. If the tank is thus filled up, and the slightly under corrected gauge made to read 20 gallons by filling right up, as was shown in that case, then the slightest movement of the car, or anybody stepping on the step, might release a bubble of air, which after reaching the petrol which is standing up in the filler and in the tank vent tower, would find its own level in the forward end of the tank, and lose half the last gallon, | ||