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).
Float mechanism, petrol levels, and flooding issues in Phantom III carburettors.
| Identifier | ExFiles\Box 93\2\ scan0105 | |
| Date | 8th October 1935 | |
| To E.{Mr Elliott - Chief Engineer} c. to By.{R.W. Bailey - Chief Engineer} c. to Da.{Bernard Day - Chassis Design} +308 Hs{Lord Ernest Hives - Chair}/Swdl.{Len H. Swindell}5/KW.8.10.35. Phantom III Carburetters. In reply to E.l/HP.3.10.35, with regard to the float mechanism, we agree that providing the same float immersion, the forces available are the same, both with the top feed and the bottom feed carburetters. As near as we can measure, the bottom feed with the .018" float gives practically the same immersion as the top feed with .010" floats, the petrol level lying approximately .100" above the centre line of the floats. We have definitely had the petrol level rise above normal through insufficient power of the float over the needle and have seen the petrol come past the needle valve momentarily, then stay at this level for a short period, then come through again. This indicates that we have very little in hand on either types of floats and probably accounts for the occasional flooding we had other than dirt on the seats. The suggestions made regarding the reduction in the needle seat area, also the weight of the needle itself, together with the increased leverage of the float over the needle, should be a considerable help to the safety factor against flooding. If float pressings can be made consistently at .010" they appear amply strong enough for the job they have to do, and there is no reason why this thickness of float should not be retained in conjunction with the other improvements. This total would naturally place the float in a higher position for the normal level, and it should be seen that in this position with the needle valve closed, the float arm should be horizontal, having a direct vertical push on the needle valve to avoid side thrust on the latter. From previous experience we have found that this feature is quite important. | ||