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).
Endurance test report on an oil pump and blower, detailing a seizure failure and subsequent analysis.
| Identifier | ExFiles\Box 179b\2\ img017 | |
| Date | 17th November 1932 | |
| -2- adjusted to feed at the rate of 1/4 pint per hour at that speed. It was found that at this rate temperature of the casing was absolutely unaffected compared with that at higher rates of feed. Whilst running, the warmest part of the casing was at the end remote from the driving end, viz: where the Oldham coupling is situated. It was noticed that this was apt to run warmer at lower speeds than at round about 4000 r.p.m. After setting the oil pump it was intended to run an endurance test comprising repeated cycles of running at 3000 r.p.m. for 50 mins. 4000 and 5000 r.p.m. for 10 mins. - one hour total. This was practically completed once, but at almost the end of the 3000 r.p.m. run the blower suddenly began to overheat and slow down. It was immediately stopped and found to be mildly seized. On dismantling it was found that the cage running inside the aluminium casing had scored on the latter at a point about two thirds of the distance from the driving end, and for a width of about half an inch. The marks extended all round the casing, but the real seizure was at one point only on the cage. All the parts were found to be well oiled. The Oldham coupling was in good condition as were also the pumping blades. The damage to the cage and casing does not appear to be serious and the parts are being cleaned up for further running. All the running with this blower has been done with petrol supplied to the carburetter, the discharge being taken to a chimney leading outside the building. The petrol has also had an admixture of one pint of oil to every six gallons, or a little over 2%. In addition a cooling fan was arranged to deliver a draught over the blower axially from the oil pump end, as would be the case on a car if fitted at the front end of the crankshaft. It appears that the oil handled by the pump should be approximately half a pint per hour, or about double the amount actually delivered, though there was no sign of abnormal heating before the failure. It seems likely that the real cause of failure was slight expansion of the cage, due to centrifugal stresses involved at the high running speed. The worst feature in the running of the blower was vibration. The Oldham coupling and pump blades set up out-of-balance forces of double the rotational frequency, and this is so severe at 3000 r.p.m. that the carburetter needle valve collar slid half an | ||