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).
Tests of twin carburetters for the Phantom II, specifically modifying the float design to prevent flooding.
| Identifier | ExFiles\Box 13\3\ 03-page341 | |
| Date | 7th September 1931 | |
| To R.{Sir Henry Royce} from Hs{Lord Ernest Hives - Chair}/Swn. c. Sg.{Arthur F. Sidgreaves - MD} Wor.{Arthur Wormald - General Works Manager} c. E.{Mr Elliott - Chief Engineer} Da.{Bernard Day - Chassis Design} c. W. x7080. Hs{Lord Ernest Hives - Chair}/Swn.1/A1R 7.9.31. TESTS OF R.R. TWIN CARBURATTERS FOR PHANTOM II. MODIFIED TO Lec. 2905/6. The main modification to the twin carburetters has been the fitting of the round type floats in order to overcome the flooding on corners experienced when using the semi-circular floats. We find that the extra weight of the floats by making them of the round type has restricted our needle valve movement such, that to have a correct level we cannot obtain the required flow of petrol through the needle valve. In order that the carburetter will not flood when stationary on an incline of 1 in 5, the petrol level should be .625 below the parting surface of the carburetter or .125 below the flood holes of the diffuser. If the carburetter is filled to this level we find that the operating rivets have only lifted the needle valves .030 and this is only obtained by removing the float buffer, otherwise we should have no movement whatever. By reducing the weight of the actuating mechanism to a minimum we were able to increase the needle valve movement to .040. It is impracticable to reduce the actual weight of the floats as they are now only .007" thickness. The LeC. shows centre line of the floats as being approximately .150 above the petrol level, but actually the centre line of the floats comes .075 below the petrol level and the effective weight of the floats is .95 ozs. against .85 ozs. with the old type of floats. If a counterbalance be used as on the "R" engine carburetters to reduce the effective float weight, it should have a moment of .65 inch-ozs. so that a reasonable needle movement of .100 - .125 could be obtained. This would necessitate a new casting for the bottom half of the carburetter. An alternative to the counterbalance weight would be to lower the base of the float chamber, even then the floats would still ride low in the petrol which is a disadvantage to flooding on corners. | ||