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).
Letter to the Autovac Mfg. Co. Ltd. regarding a complaint about slow speed light running issues with the 'Autovac' system.
| Identifier | ExFiles\Box 40\4\ Scan240 | |
| Date | 28th May 1925 | |
| COPY. Hs{Lord Ernest Hives - Chair}/AJLL/LG. 28th. May 1925 The Autovac Mfg. Co.Ltd., Heaton Norris, Stockport. Dear Sirs, We have recently received a complaint of the 'Autovac' action affecting the slow speed light running of our cars. This trouble we find is present on all our cars which are fitted with vacuum feed, although the extent of the interference with smooth running varies on different cars. We should be pleased if you could let us know if you have ever experienced the same failing, and if so, can you offer any suggestions which would overcome it? Having investigated the matter slightly, we imagine what happens is as follows :- The engine having been run light at very slow speeds for a little time, the Autovac is fitted completely, the petrol levels in the inner and outer chambers are identical; the suction valve being closed and the air release valve open. Now as the engine continues to run, the petrol level in both chambers of the Autovac fall together until the float has fallen sufficiently to overcome the lag in the action of the valve toggle mechanism (this amounts to approx. .250" float movement), and so operates the valves again. The air valve closes and the suction valve opens, air is exhausted from the space above the petrol in the inner chamber, into the induction pipe carrying with it a certain amount of petrol vapour. We find that this petrol mixture sucked into the induction is sufficient to strengthen up the carb. mixture in such a manner as to cause a momentary unevenness of running of the engine. There is, of course, no trouble like this at high speeds or full throttle work, it only occurs at quite slow light running speeds when the slightest variation in induction pipe mixture can affect the smooth running of an engine. We find that it does not occur to such an extent when the petrol level in the Autovac is low, in which case the level in the inner chamber would be very low at the point when the air release valve is closed and contd :- | ||