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).
Inadequacy of PI shock absorber replenishing valves and proposed modifications to prevent knocking.
| Identifier | ExFiles\Box 68\2\ scan0257 | |
| Date | 10th September 1930 | |
| x8520 ROLLS-ROYCE OF AMERICA, INC. SPRINGFIELD, MASS. Oy-1 Sept. 10, 1930. Rolls Royce, Ltd., Derby England. Attention: Rm.{William Robotham - Chief Engineer} Cc-Btn. Shock Absorbers - Sec. 7150/60 We have a fairly well developed suspicion that the replenishing valves on our present PI shock absorbers are on the thin edge of being inadequate to do their job. Even when everything is perfect, we do not know that they are adequate to supply under atmospheric pressure the leakage at the piston which can occur under severe use, and very slight errors in workmanship such as horizontal delivery passage from valve to cylinder slightly low, (making it necessary to set the valve with less than the full lift) or a piston on the low limit with cylinder on the high limit (causing excess leakage) will give a condition where "lost motion" can be produced in the instrument even by hand. This lost motion is of course due to voids caused by inadequate replenishing and produces severe knocking of a very elusive type. By reboring the replenishing valves with .218 ball, .266 chamber around ball, .156 passage below ball, and .187 horizontal passage to cylinder (see print attached) Btn. appears to have eliminated these knocks or at least reduced their occurrence to extreme conditions which we have not yet produced. Just as a suggestion, we should consider that PII vertical dampers, which have only one replenishing valve, would develop such knocks very readily unless the fit of the lower piston guide was extremely close. (Continued) | ||