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).
Piston ring design, comparing different types to improve gas tightness and prevent crankcase vapour.
| Identifier | ExFiles\Box 77\3\ scan0231 | |
| Date | 1st April 1920 | |
| Contd. -5- 2 Hs{Lord Ernest Hives - Chair}1/LG12.4.20. fitting portion of the piston assisted in holding the gas. The gas which leaks past a piston gets by the stop or joint than round the band between the rings to the next stop and so on until at the bottomstop there is an oil return hole directly underneath it. It is there that the gas leaks into the crank-case. We find there is an advantage in increasing the number of rings so that the alteration in the rings to prevent the pistons binding on the top band will also help us as regards gas tightness. The cast iron pistons of the split type are no better for holding the gas and they are worse as regards crank case vapour, because the tops being somhot they vapourise a portion of oil which is thrown upon them. If we take an old type piston which appears to hold the gas very well and turn an annulus and drill the oil return holes below the bottom, ring, one can hear the leakage past the rings distinctly. We attach herewith a table showing the difference in HP. at very low speeds with different number of rings fitted. There is also a table showing the differen e in HP. with cast iron and aluminium pistons. Hs.{Lord Ernest Hives - Chair} | ||