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 describing a suction-fed carburetter that combines carburetter and vacuum fuel supply functions.
| Identifier | ExFiles\Box 122\4\ scan0028 | |
| Date | 1st November 1921 | |
| Reprinted from "The Commercial Motor," November 1, 1921. A SUCTION-FED CARBURRETTER. An Instrument Combining Carburetter and Vacuum Fuel Supply. A CARBURRETTER which embodies many novel features and yet is withal quite simple has been designed by Mr. F.{Mr Friese} H.{Arthur M. Hanbury - Head Complaints} Arnott, and is being manufactured by Carburvac, Ltd., 28, Grange Road, Willesden, N.W.2. This interesting device is not only a carburetter in the strict sense of the word, but is arranged so that it can feed itself with petrol by suction from a tank placed below the level of its float chamber. It thus embodies a principle somewhat similar to that used on the separate type of vacuum fuel lifting device. In order that this can be achieved, the float chamber is isolated from the atmosphere, except for a small passage which connects it with the vacuum chamber of the carburetter. When the engine is cranked—or turned by a self-starter, and the throttle valve opened slightly, a partial vacuum is created, and the same degree of vacuum is communicated to the float chamber, so that petrol is drawn into the latter from the tank. The level of petrol in the float chamber is determined in the usual way—by a float and needle. This is an extremely simple method of lifting the fuel, which certainly proves efficient in practice, and cuts out an expensive accessory. As regards the rest of the carburetter, there is a central chamber containing a fluted needle, at the lower end of which is formed a cone ending in a taper. This needle is held down on its seating by means of a light spiral spring, which takes its bearing on a small dashpot fixed to the top of the needle. A chamber at each side of this dashpot is in communication with the float chamber, and thus the needle is prevented from vibrating and the air valve from fluttering. The chamber itself is, of course, sealed from the outer air. At its lower end the outer portion of the central chamber is machined, and over it slides a small piston which forms the air valve and also lifts the spring-loaded needle off its seat as it rises under the influence of engine suction. Normally, although the coned seating of the needle is below the level of the float chamber, petrol is prevented from leaking, owing to the action of the spring. There is a clearance of approximately 1/8 in. between the air piston and the tapered end of the needle, but, as the throttle is opened, the piston rises, and, thrusting the needle upwards, allows petrol to flow down by gravity into its centre. At the bottom of the piston are cut long slots, through which the petrol is sucked, and, mixing with the incoming air, is carried through the mixing chamber to the throttle. It will be seen that this carburetter is of the constant vacuum type. The coned orifice through which the air enters the mixing chamber, and which acts as a seating for the air piston, is formed as a separate sleeve, which is held into the body of the carburetter by means of a large square thread cut in the body and on the exterior of the sleeve. The distance that this piece is screwed into or out of the carburetter controls the supply of air and affords a means of altering the mixture to suit the conditions. On the body of the carburetter are marked two arrows, and these are the limits of the range of mixtures from weak to strong which can be achieved by turning the screwed piece; this is cut with ratchet teeth, meshing with a spring tongue screwed to the body of the carburetter, in order that its position can be fixed to a nicety. There are no parts on this carburetter which can suffer rapidly owing to the effects of wear. The turned portion of the central chamber, on which the air piston bears, merely acts as a guide, and no troubles owing to jamming of the piston are likely to occur. We recently examined a Ford van fitted with this carburetter, and were agreeably impressed by its performance; the acceleration was excellent and the engine ticked over without the slightest hesitation or misfiring, the vehicle being capable of proceeding at a walking pace on top gear. We were unable to make any tests as regards the economy of the instrument, but understand that very remarkable results have been achieved, the Ford van we inspected being said to average 34 m.p.g. Part sectional view of the Carburvac instrument, showing the spring-loaded needle-valve and piston air valve. Temple Press Ltd., 7-15, Rosebery Avenue, E.C.1. | ||