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).
Technical explanation of oil leakage and valve riding in hydraulic tappets, comparing different tappet designs.
| Identifier | ExFiles\Box 17\6\ Scan303 | |
| Date | 4th September 1934 | |
| -2- For an engine fitted with hydraulic tappets the maximum possible engine speed would be the minimum speed at which the valve gear rode if it were not for oil leakage from underneath the plunger, since at this speed the valves would be held off their seats by an increasing amount. With oil leakage occurring the critical speed at which the valves are held off their seats is the lowest speed at which the valve riding is so severe that more oil is taken past the plunger valve during the riding period than can be leaked away during the rest of the lifting operation. With the Halford type of tappet, with its high leakage factor, this condition is never attained, and the critical speed is the bouncing speed as it would be with standard tappets. In the case of the G.M. type of tappets, it would seem that the poppet valve passes less oil for a given severity of valve riding than the ball valve. The probable reason for this is illustrated in the accompanying sketch. | ||