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).
Comparison of plunger and casing designs between R.R. and Cadillac, analysing leakage factors.
| Identifier | ExFiles\Box 106\5\ scan0068 | |
| Date | 12th September 1932 | |
| -2- (a) The bushes having, perhaps, to small a clearance and forcing the plungers down. (b) Air being trapped inside the plunger. (c) Lekage being too great necessitating the continual filling up of the oil weel below the plunger. (d) Leaking Plunger Valves. The design of the R.R. plunger is by no means similer to Cadillac design, whereas our plunger has a groove half way down with holes drilled through to the inside, presumably to allow air to escape should any be trapped, the Cadillac is just a plain plunger with no provision for allowing trapped air to escape, and we think that since the Cadillac design is quite successful the provision of a groove is quite unnecessary. We quite realise that the R.R. casing is by no means as long as the Cadillac and that having a Plunger of our design it is easier to fit in the Plunger return spring but we think it could be dispensed with by using a flat wire return spring. The clearance between the Plunger and its casing is of great improtance since while all the Plungers may be steady with the oil cold several of them can be seen to be continually moving up and down when the oil is hot. This fact seems to suggest that we should have a definite relationship between the clearance and the effective length of the Plunger below is given a comparison of R.R. and Cadillac Plunger based on the leakage factor being cross sectional area between Plunger and Casing / Effective length of Plunger. Leakage factor R.R. Cadillac. .002967 .001255 From this it will be seen that Lekage Factor on the R.R. Plunger is approximately 2.3 times that of Cadillac. One way of compensating for the difference in Viscosity of the oil hot and cold would be to have a Plunger made of say Bronze so that the Plunger would expand relatively more than the cylinder with the change of oil temperature, but Cadillac do not use Bronze Plungers | ||