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 Autovac Mfg. Co. Ltd. concerning significant variations in petrol delivery performance between different Autovac units.
| Identifier | ExFiles\Box 40\4\ Scan194 | |
| Date | 7th January 1927 | |
| X/55F. Expl: Dept: HS{Lord Ernest Hives - Chair}/AJL1/LG. 7th. Jan. 1927 Messrs. The Autovac Mfg. Co.Ltd., Stockport. Dear Sirs, We have recently had instances of our cars on dynamometer test running short of petrol under conditions where we expected the Autovac to supply the full engine demand. Careful tests comparing several autovac units have shown us that there is a very considerable variation in petrol delivery from different units. As an example we give the result of one test comparing two autovac units under exactly similar conditions :- Engine RPM. = 1500. Induction pipe depression = 1.9" mercury. Petrol lifted through 32". Autovac petrol delivery :- No.1. Unit = 40 pts/hr. No.2. Unit = 65.4 pts/hr. In order that there should be no false result caused by an imperfect non-return valve in the suction line, the same suction elbow was used in each unit. The depression in each unit was also similar viz: 2.9" Hg. yet the petrol delivery was widely different. Further tests were carried out in which the floats were interchanged but with no change in result. The only difference we can find between the units is the length of valve travel and hence length of float stroke. We find that by altering the valve travel we can very materially alter the petrol delivery, the longer stroke giving a better petrol delivery. The valve travel on various units appears to vary between 3/32" and 3/64" hence the float stroke varies by approximately four times this movement. contd :- | ||