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).
Causes of knocks in shock absorbers, related to lever bearing slack and the size of a low-pressure side hole.
| Identifier | ExFiles\Box 28\1\ Scan120 | |
| Date | 26th March 1928 | |
| To OY. from Hs{Lord Ernest Hives - Chair}/Rn.{Mr Robinson} +832 Hs{Lord Ernest Hives - Chair}/Rm{William Robotham - Chief Engineer}2/LG26.3.28. SHOCK ABSORBERS+ X235 With reference to your note of the 8th. You will recollect that we gave you all the information we had on noises from the shock absorber in our Hs{Lord Ernest Hives - Chair}/Rm{William Robotham - Chief Engineer}2/LG23.4.27. In this note we mentioned the fact that if the lever bearing was slack even to the extent of .003, it would be sufficient to cause a knock. Since we introduced the gravity feed to the bearings we appear to have reduced the wear, and as a matter of fact have not been troubled with knocks at all lately. The .025" hole on the low pressure side was actually evolved to eliminate a knock and therefore, at the moment, we cannot believe that you will overcome your troubles by reducing the size of this hole. We will carry out an experiment however having a pair of .025" holes in parallel which will reduce the amount of oil we can pass through due to the viscosity effect but will not obstruct the passage of the air. We do not think slow movement of the shock absorber lever by hand gives a true representation of what happens to the shock absorber at speed because the small air escape has a very high viscosity factor and so its delivery falls off very rapidly with speed, while the replenishing orifice has not this characteristic as it has a reasonable diameter. Additionally of course the shock absorber never works slowly on the road therefore we are not very interested in this condition. | ||