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' detailing constructional alterations and improvements to the Autovac fuel system.
| Identifier | ExFiles\Box 40\4\ Scan016 | |
| Date | 5th June 1920 | |
| X.13579 THE AUTOCAR, June 5th, 1920. 1057 Autovac Improvements. Constructional Alterations designed to Improve a Popular Apparatus. WHEN a new component finds its way into the standard equipment of the motor car, at the outset two things usually happen. The theorist greets it as a marvellous improvement, the practical man as a new source of trouble. Until the new fitting has consolidated its ground, both are well founded in their views. The theorist understands, but does not use, the practical man uses, but does not always understand, hence the component often receives treatment the reverse of sympathetic. With the Autovac, for example, it is possible to get into trouble that appears far more serious than is really the case. A prolific instance occurs when the vacuum tank is allowed to run completely dry. Then it is not possible to start the engine instanter, as it becomes necessary first of all to draw petrol through to the Autovac. Theoretically, a few revolutions of the engine by means of the starting handle, with the throttle closed, should be sufficient to fill the tank, but it sometimes happens in practice that a few minor troubles, insufficient to matter in the ordinary, will combine to prevent that desirably easy end, and the motorist is for the moment at a dead-lock. This, however, is best overcome by removing the connection which couples the Autovac to the pipe line running to the main tank, and pouring in a little petrol for starting purposes. Incidentally, it would be an improvement were the Autovac fitted with some reserve fuel device, such as that becoming increasingly popular with gravity fuel main tanks, wherein there are two cocks leading to the carburetter supply, the one normally in use being connected to an outlet pipe sufficiently far above the bottom of the tank never to drain the latter completely, whilst the second cock permits the reserve thus trapped to be used in emergency. [Image 1: A section through the Autovac tank showing the toggle mechanism of the valves and the flap valve.] Diagram Labels: PETROL SUPPLY, TO INDUCTION PIPE, AIR VENT, FLAP VALVE, DRAIN PLUG, TO CARBURETTER. The Working of the Autovac. In the latest design of Autovac improvements have been made in the toggle gear of the valves, the design of the outlet flap valve, the float, and the drain plug. The principle of the apparatus remains unaltered, and is worth recapitulating briefly because of the number of users to whom the working is not clear. When a main petrol tank is carried low down in the chassis, it becomes necessary to raise petrol from it up to the carburetter, the pressure or head of petrol remaining more or less constant. In the vacuum-feed system, normal atmospheric pressure actually does the work, there being at the upper end of a petrol supply pipe from the main tank a connection which runs into the main inlet pipe of the engine. The vacuum or depression in the inlet pipe when the engine is running ensures that the air pressure at the upper end of the petrol supply pipe is less than the atmospheric pressure in the main tank, hence atmospheric pressure forces the petrol up the supply pipe. The petrol thus obtained is trapped in a chamber containing a float, and when a given quantity is collected the float rises, and kicks over two valves, one of which cuts off a further supply of petrol whilst the other admits the air to the chamber, and thus allows the petrol to flow out past an automatic flap valve at the bottom into a lower chamber open at the top to the air and connected at the bottom to the carburetter, whence the fuel flows by gravity. As the top chamber empties the float falls and the action recommences. Ingenious Valve Operation. In order that there shall be no "hunting" there is between the float and its two valves a toggle device which causes the action to be positive and quick at the top and bottom positions. This toggle arrangement has now been simplified, and, as shown in the sketch, has only a single spring and stirrup bar instead of the original compound arrangement. [Image 2: A section through the new self-emptying float.] Diagram Labels: HOLLOW SPINDLE, FLOAT, SMALL PUNCTURE. Slightly increased in size, the metal float is now made so that it will, if punctured at the bottom, automatically empty itself without detriment to the operation of the apparatus. This is achieved by providing in the hollow float stem a small hole at the top and a similar hole in the lower portion of the stem inside, and nearly at the bottom of the float. The upper hole comes under the influence of any depression existing in the top chamber; hence any petrol collected inside the float is drawn out through this hole. We have seen a well-punctured float working in an experimental glass tank, and can speak of the gush with which the petrol issues from the top hole in the spindle during the suction phase. Autovac tanks are all tested after manufacture under a five inch vacuum against the time taken to fill the top chamber. An improvement has been made in the self-centring flap valve, the arm of which has been stiffened by means of an additional rib stamped in. The original drain cock situated in the base of the bottom chamber has now been superseded by a form of needle valve, of which the details are here illustrated, the new form being less liable to "weep." In conclusion, it may be mentioned that the Autovac is now being made in a new and separate factory, and that the output is nearly one thousand sets of apparatus per week. The makers are Arundel and Co., Sovereign Works, Stockport. D29 | ||