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).
Tests comparing the spring motion of dual and triple springs, noting coil surging and bunching.
| Identifier | ExFiles\Box 43\3\ Scan115 | |
| Date | 13th January 1927 guessed | |
| contd :- -3- Tests made with similar parts in which the oscilloscope was used to observe the spring motion did display a marked difference between the dual and triple springs. Violent surging of the coils was manifest with the triple springs - outside coils - while this was nowhere near so severe with the double springs. Consider the triple springs :- When the tappet struck the valve it seemed that the lower coils remained stationary while the top ones - those nearest the spring washer - bunched together. After a small lift - probably after the acceleration period - the coils separated out and bunched together at the bottom, surging together again on the closing period. There was much less surging with the double springs and the vibration of the coils seems to have both a smaller amplitude and higher period. This 'bunching' phenomenon seems a reasonable explanation of the breakage as although the static stress range is less with the triple springs the 'bunching' of coils would result in a +ve and -ve stress alternation in the coils at the ends of the spring also a large number of reversals per minute. It is interesting to note that nearly all the breakages have taken place at the coils near the ends of the spring. From the above tests it seems reasonable to suppose that the static stress range is of little consequence compared with the surging of a spring which could result in a considerable multiplication of the static stress and increasing the reversals. contd :- | ||