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).
Technical report discussing the development and comparison of different fuel feed systems, including gravity tanks and various petrol pumps.
| Identifier | WestWitteringFiles\V\2January1931-April1931\ Scan054 | |
| Date | 12th March 1931 | |
| - 2 - We have not had a scheme for the fuel feed system but we understand it was intended to use a small gravity tank on the dash, supplied by the pump. The new twin choke carburetter is situated considerably higher than the std. chassis carb. and we do not think the gravity head obtainable would be sufficient for reliable operation. In any case it would necessitate much larger needle valves in the float chamber and these are always more prone to flooding trouble. With the car climbing a steep hill the gravity head would be considerably reduced. We much more favour the direct feed from the pump which is the usual practice with petrol pumps. As the P.II petrol pump is at present, it cannot be used direct to the carburetter. With the bellows spring in position the fuel pressure amounts to 10 lbs/sq.in. Removing this spring and relying only on the spring of the bellows to feed the petrol we get a pressure of 8 lbs/sq.in. We are next going to try a counter spring within the bellows in order to reduce the fuel pressure down to about 4 lbs/sq.in. With the pump working direct on the carburetter it is essential that it should possess a quick "pick up" with an empty pump which condition is obtained after running dry on the main fuel tank. Chryslers are fitted with an A.C. fuel pump and with the carburetter and strainer empty and using the starter motor petrol appears at the filter in 5 secs. and the engine will start to fire in 9 secs. In this system the A.C. pump is connected directly with the carburetter. The A.C. pump has max. .25" stroke of the diaphragm and its large capacity we think is the reason for its quick "pick up" with a dry pump. With a large capacity we think the action would be less dependent on such fine setting of the valve lift & valve spring loads. The A.C. pump employ a fabric diaphragm and at max. stroke (¼") practically fills the pump chamber so that in the downward movement a high suction is obtained to give a good "pick up" with an empty pump. This fabric diaphragm seems quite reliable in service and is of similar material to that used in the "Petroflex" tubing used for aircraft installations. For large strokes we should anticipate it to be more reliable than the metal bellows of our pump. At the present moment we are in the difficulty that we have developed the twin choke carburetter that it is now ready for preliminary road tests on a car but we have not a satisfactory fuel system for it. For the time being we are | ||