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 describing the Autovac petrol feed system.
| Identifier | ExFiles\Box 40\4\ Scan001 | |
| Date | 5th July 1919 | |
| X 3549 8 THE AUTOCAR, July 5th, 1919. The Autovac Petrol Feed System. A Device which Permits Placing the Fuel Tank in Any Convenient Position. IN the great majority of cases in which it has been found undesirable, owing to the design of the car—or, possibly, to the conservatism of its designer, or of the motoring public—to place the fuel storage tank in any position other than below the level of the carburetter, it has been the general practice to force the petrol upwards to the float chamber either by the pressure supplied by a mechanically driven air pump, or else through the agency of pressure created in the tank by exhaust gases admitted via a small branch pipe from the exhaust manifold on the engine. Advantages Claimed. Both these methods suffer from a common defect, since, if the pressure in the tank should by mischance fall below a certain point, owing to a leak, the petrol feed to the carburetter becomes intermittent and causes engine trouble almost immediately, and necessitates the regular use of the hand pump until the leak is found and eliminated. The primary advantage of the Autovac system is that a steady and continuous supply of petrol can be fed to the carburetter from a storage tank below the level of the engine without the usual disadvantages of pressure feed, while, incidentally, as a further advantage, it can also be used in connection with gravity tanks which fail—as they not infrequently do—to give a sufficient head of petrol to the carburetter on very steep gradients. The general features of the vacuum feed tank employed in the Autovac system will be gathered from the illustrations, which also show the layout of the piping in the complete system. Mounted in any convenient position on the engine side of the dash, above the level of the carburetter, is a small cylindrical tank divided into two chambers, upper and lower, as shown in fig. 2. The upper chamber is smaller in diameter and capacity than the lower, and both chambers are closed by a lid{A. J. Lidsey} between which and the tank is a rubber washer to form an air-tight joint. Inside the inner chamber is a light metal float, which is connected by its central spindle to a pair of coil springs and toggle levers supported on two fulcrum pins on the underside of the lid{A. J. Lidsey} of the tank. There are in the lid{A. J. Lidsey} of the tank two small valves that are connected by pins to one of the toggle levers just referred to, one valve (vacuum) having a seating on the underside of the tank lid{A. J. Lidsey}, while the other (atmospheric) has its seating on the upper side. The lower extremity of the float spindle is situated at the base of the inner chamber in a tube, at the end of which is fitted a hinged flap device. How the System Works. On the outer face of the lid{A. J. Lidsey} of the tank are conical joints arranged to take three fittings: A, an elbow pipe connection above the vacuum valve leading to the induction pipe of the engine; B, an air vent pipe above the atmospheric valve; and C, an elbow pipe connection leading from the interior of the inner chamber to the main petrol storage tank. There is also a small channel, shown at E in fig. 2, drilled between the lower or outer chamber and the joint above the atmospheric valve in the lid{A. J. Lidsey} of the tank. In the base of the lower chamber is fitted a tap for drainage purposes, and an elbow pipe connection to the pipe supplying the carburetter. The general arrangement of the complete Autovac petrol and vacuum pipe system will be seen in fig. 4. The continuous supply of petrol to the carburetter from the main storage tank in the Autovac system is carried out entirely by the partial vacuum created in the induction pipe of the engine; and fig. 1 illustrates diagrammatically how the apparatus operates from the moment the system is brought into action when the engine is started. The Autovac vacuum tank. Fig. 1.—Sequence of operations in the vacuum tank. A, pipe connection from upper chamber to induction pipe of engine. B, air vent in communication with upper and lower chambers. C, pipe connection between inner chamber and large petrol tank of main supply of petrol. D, supply pipe between lower chamber and carburetter. This diagram also shows the action of the float and lever mechanism operating the valves. B28 | ||