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 from 'The Autocar' magazine detailing the operation of the Autovac vacuum petrol feed tank system.
| Identifier | ExFiles\Box 40\4\ Scan003 | |
| Date | 5th July 1919 | |
| THE AUTOCAR, July 5th, 1919. Previous to the engine being turned over on the first occasion, and the system brought into operation, the upper and lower chambers of the vacuum tank will be dry. In these circumstances, the float will sink to its lowest position in the upper chamber, opening the vacuum valve, and closing the atmospheric valve in the lid{A. J. Lidsey} of the tank. If the engine is now rotated by hand, the suction from the induction pipe through the pipe A (fig. 1) will exhaust the air in the upper chamber, and the partial vacuum created will suck petrol up from the main tank through the pipe C, and fill the inner chamber, as seen in operation 1(1). This action goes on until the float rises to such a level that it automatically shuts off the vacuum valve, and opens the atmospheric valve through the motion of the two toggle levers and springs above the float, shown in the diagram (2). As soon as the vacuum and atmospheric valves are closed and opened respectively, the partial vacuum in the upper chamber is immediately dissipated by air passing in through the vent pipe above, with the result that the return to normal atmospheric air pressure allows the quantity of petrol in the upper compartment to sink by gravity into the lower chamber past the hinged flap valve, and thence through the pipe D to the carburetter. While the transfer of petrol is taking place between the upper and lower chambers, the float has been sinking; and when it reaches a certain point, the vacuum valve is opened and the atmospheric valve closed, thereby causing the suction of the engine to charge the upper chamber with petrol again from the main storage tank, as seen in the diagram 1(3). In this phase of action in the tank, the flap valve at the lower end of the upper chamber is automatically closed by the partial vacuum above, and does not open again until the upper chamber is once more filled with petrol, and the partial vacuum has again been dissipated by the opening of valve B, as illustrated in diagram 1(4). It will be seen that, as the vacuum and atmospheric valves open and close in concert with the float, the upper chamber constantly charges the lower chamber, and thereby gives a regular and continuous flow of petrol under gravity to the carburetter, the drilled passage shown at E in fig. 2 serving to eliminate air pressure in the lower chamber during the process of charging it from the upper chamber. The spring and toggle lever arrangement in the latest pattern Autovac tank, illustrated in figs. 2 and 3, has been found to be considerably more efficient than the mechanism fitted to the original tank, since there are fewer joints to wear, and the valves themselves cannot rotate and so cause leakage between their faces and their seatings. A special form of filter has been incorporated in the elbow connection in the vacuum tank leading to the main storage tank, while a small non-return valve of the flap type is introduced in the elbow fitting above the vacuum valve to prevent backfires from the engine induction pipe interfering with the normal operation of the vacuum system. Minor Improvements. Other alterations in the design of the Autovac consist of a general reduction in the size and bulk of the tank for convenience in installation, while a central clamp and nut on the lid{A. J. Lidsey} of the tank enable the two elbow connections and vent pipe to be swivelled in any direction required when arranging and connecting pipes. The flap valve at the base of the inner chamber in the tank is also of a new and improved design, so arranged that the flap cannot, under conditions of fair treatment, stick by reason of sediment passing through the inner chamber. In ordinary circumstances, the amount of petrol remaining in the tank and in the carburetter together allows the engine to be started immediately, prior to the action of the Autovac tank commencing under the effect of suction. The complete Autovac vacuum feed tank and fittings are well made from suitable materials of the best quality, and finished in the most workmanlike manner; in addition to which the convenience of the user is considered in so far that the fullest instructions for the installation and efficient maintenance of the system are issued in commendably intelligible booklet form by the manufacturers and patentees, Messrs. Arundel and Co., Sovereign Works, Stockport. Fig. 2.—Sectional view showing upper and lower chambers and valve mechanism in lid{A. J. Lidsey} of tank. Fig. 3.—The float operates the vacuum and atmospheric valves through two bow shaped levers and a pair of coil springs. Fig. 4.—Piping arrangement of the vacuum petrol feed. The arrows indicate the flow of the petrol from the main tank via the vacuum chamber to the carburetter. B31 | ||