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).
Limitations of the vacuum feed system for the 40/50 HP chassis, particularly at high altitudes.
| Identifier | WestWitteringFiles\J\May1923\ Scan36 | |
| Date | 9th May 1923 | |
| To R.{Sir Henry Royce} from Hs.{Lord Ernest Hives - Chair} c. to CJ. c. to E.{Mr Elliott - Chief Engineer} c. to Da.{Bernard Day - Chassis Design} c. to BY.{R.W. Bailey - Chief Engineer} ORIGINAL. VACUUM FEED FOR 40/50 H.P CHASSIS: X3579 We have three 40/50 H.P. cars running fitted with the vacuum feed. So far we have had no trouble. We attach hereto charts which show, however, the limitations of the vacuum feed. If we adopt the vacuum feed we must expect that under certain conditions the petrol supply will fail, for instance, Springfield state they are selling a number of cars in Denver City which we understand is 5000 ft. altitude and the roads outside reach an altitude of 14,000 ft. We should not expect the vacuum feed to work satisfactory under those conditions. There are three main points against the Autovac system at high altitudes. (1) Percentage decrease in the height to which the petrol can be raised. (2) Larger throttle opening is called for to produce a given tractive effort, thus further reducing the depression communication to the Autovac. (3) Increase amount of full throttle work, consequently reducing the opportunities of recuperation. Another point against the Vacuum feed is that if it goes wrong, it is very difficult for the average driver to locate the cause of the trouble. We must say, however, that the Autovac on the 20 HP. has proved to be wonderfully reliable - we have not had a single instance of any trouble once it has been fitted up correctly. contd:- | ||