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).
Analysis of engine valve failures, including observations on colour, temperature, and fracture causes.
| Identifier | ExFiles\Box 179b\3\ img333 | |
| Date | 14th January 1933 | |
| -2- He/Pur.9/W.H.14.1.33. Cont'd.{John DeLooze - Company Secretary} A new valve was fitted and the running continued and the mixture was richened considerably, the specific consumption being increased to .620 pts/Hr. Valve clearance checks were made and shewed no variation, and after a further three and a half hours running from the previous failure, No.6 B. front exhaust valve failed in a similar manner to the previous valves. Observations of the valves which had failed shewed rather peculiar symptoms, in most of the cases the failure taking the form of a section of the valve head half an inch long on the periphery of the seat and extending up to a quarter of an inch into the head being missing. The remainder of the head was practically free from warping and shewed very little signs of burning. It was also noticed that the inner edges of the failure supposed to be burst, were fairly regular and not fused as one would expect, but gave every indication of fracture. In this respect, after the final failure on Kestrel 25 engine, the exhaust manifolds were removed from B.side block and further running at full throttle was carried out to observe the approximate temperatures and conditions of the valves when running, also to note if further fusing took place on the valve which had already failed, at the same time two other valves were run with no tappet clearance to note effect. A further 30 mins. running at full throttle 2750 R.P.M. and developing just over 900 BHP. took place and the results obtained were very interesting. The colour of the valves was a bright cherry red throughout, indicating an approximate temperature of 700°C. This colour was continuous over the whole of the valve heads which were visible and exposed to the exhaust flames, the seat rims being just slightly darker than the rest of the head, and contrary to expectation the valves with no tappet clearance shewed no signs of being hotter than the rest. Observations of the valve which has already failed, seemed to support a theory that the initial cause of the failure is a fracture of a part of the valve head which gives the indication of burning by fusing afterwards due to the high velocity of the exhaust gases passing through the small orifice made by the fracture. This was borne out on the observations, by the general temperature of this valve being only slightly higher by colour than the rest, but the exhaust edges of the orifice, being sharp from the hardened fracture, were incandescent and the metal was fusing with a bluish-white colour of the consistency of an oxy-acetelene flame equivalent to a temperature round about 2000°C. | ||