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 the advantages of hairpin type valve springs versus helical type springs.
| Identifier | ExFiles\Box 158\5\ scan0030 | |
| Date | 30th March 1939 | |
| -2- The hairpin type valve spring has several advantages over the helical type. Firstly the dynamic effect of the mass of the spring is less, thus slightly raising the bouncing speed of the valve. With the given examples of each type of spring this difference is very small the effective weights being .0447 lb. and .0404 lbs. for the helical and hairpin springs respectively and the amount that the bouncing speed would be raised is very slight. This might be increased by increasing the loading on the valve up to the limit imposed by the safe working stress of the material. A second advantage is that by modifying the design of the spring it would be possible to reduce the length of the valve stem for any given seat loading. This would have the effect of increasing the bouncing load also. The main advantages of the hairpin spring apply to air cooled single or twin engines more than to the multi cylinder water cooled engine where the space required has limited its application and at the present time no car manufacturer seems to be fitting them. Rm{William Robotham - Chief Engineer}/J.R. Spooner. | ||