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 explanation of the AMAL Piston fuel pump.
| Identifier | ExFiles\Box 27a\2\ Scan056 | |
| Date | 4th November 1931 guessed | |
| The AMAL Piston — a definite improvement on P.I.F THE INSTRUMENT EXPLAINED (Please read in conjunction with Figs. A and B on Pages 4 and 7). This pump is of the direct-acting type, driven by an eccentric cam giving a stroke of .25 to .28” (6.5 to 7 mm.). The most novel points in the design of this pump are the total elimination of all fabric diaphragms, and positive arrangements have been made for the absolute prevention of any possibility of fuel leaking past the pump into the engine crank case, together with a definite control of the pressures attained by the fuel delivered to the carburetter. The functioning of the instrument can be followed from the sectional general arrangement shown herein. The eccentric cam A is generally formed on the camshaft of the engine, and is therefore driven at half engine-speed. This cam actuates a plunger B which is kept in constant contact with the cam by means of the return spring C. The plunger is connected to the piston D by means of a collar in such a manner that the piston is given a positive suction stroke by the return spring C, but its delivery stroke is regulated by the piston control spring E.{Mr Elliott - Chief Engineer} Fuel is fed from the tank to the pump by the pipe F, which has an external diameter of 5/16” (8 mm.) passing through the loading valve G, and thence by the passage H to the filter chamber J, and through the fine gauze screen to the section valve K.{Mr Kilner} The return stroke of the pump forces the fuel through the delivery valve L, and so to the carburetter through the pipe M, which also has an external diameter of 5/16” (8 mm.). The fuel may also pass through the port N and the passage O to a pressure control valve P, and any excess of fuel not required by the engine is returned to the fuel tank by the pipe R, which has an external diameter of 5/16” (8 mm.). The return pipe R has also a second function to perform, that is—as the delivery from the pump is continuous irrespective of whether the carburetter is taking fuel or not, there is no possibility of gasification setting up in the supply pipe owing to the pump being subjected to heating effects either by conduction or radiation from the engine. The loading valve G, previously described, on the inlet pipe to the pump is for the purpose of maintaining a depression or suction in the whole of the filter chamber J and the connecting passages H and U, also the groove formed by T in the body of the pump, at all times and conditions when the pump is in operation. It will thus be obvious that any fuel which may pass the piston on its delivery stroke is trapped in the groove T formed in the body of the pump and returned to the filter chamber J through the passages U. Also any fuel which may tend to pass the front edge of the piston is prevented from doing so by the depression or suction mentioned above. It will be noticed that the whole of the control valves are of extremely simple construction, simply being 7/32” diameter stainless steel balls and, in an emergency, ordinary 7/32” steel balls, which can be readily obtained from any local store, may be fitted, and these will last, for all practical purposes, for a long period of time. It will also be noted that there is a total elimination of light springs in the valve mechanism, which are so apt to give trouble, the only loading mechanism employed on the valves consisting of two small brass weights, which are interchangeable, as are the plugs on either side of the pump, so in case of dismantling it cannot be assembled incorrectly. FITTING. The stroke of the pump, as previously mentioned, is .25” to .28” (6.5 to 7 mm.), and the correct setting of the pump when fitted to the engine can easily be verified by removing the screw W. No fabric diaphragms. No leak 1 | ||