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).
Investigation and resolution of noise issues in a double piston damper during testing.
| Identifier | ExFiles\Box 182\M19\ img081 | |
| Date | 1st June 1931 guessed | |
| N.SCH.3190 & 5. DOUBLE PISTON DAMPER. Before fitting it on to test rig (during the filling process) it was noticed that the loads were exceptionally heavy, there was no air release and that when the light springs were fitted in place of the valve springs issued to facilitate the filling operation, movement of the main lever caused a harsh grating sound to emanate from the body of the damper. This occurred on the high pressure or rebound stroke. The noise was very pronounced when the damper was fitted on to the rig and using a 1" stroke at over 40 RPM; the standard valve springs were replaced after the filling operation. It was thought that air in the pressure chamber was in some measure responsible for the noise. To prove this, four grooves (.032" dia. X .032" deep) equally spaced were cut along the full length of the low pressure piston, these had no effect. Changing the pistons over was also useless. A pair of pistons .005" undersize on diameter also had no effect in reducing the sound. The valve was then fitted with a long threaded stem to provide external adjustment, the syphon and cover being replaced by a flat piece of 1/4" steel plate through which the stem was screwed. By this means the valve was raised .005" from its seat and locked in that position thus forming a restricted orifice, instead of a spring operated valve. With this apparatus the noise ceased, also the diagrams returned to the base lines instead of running "in the air" as previously. Reverting to the spring operated valve, a small hole .015" dia. was drilled through the L.P. valve, the noise returned. When this hole was increased to .025" dia. the offending noise vanished, and the diagrams again returned to the base lines. During the noisy periods the diagrams were distinctly waved, and this always shewes on the H.P. stroke. The stroke was then increased to 4" and with the .005" pistons still in position, also the .025" hole in the H.P. valve, the damper was quiet. Standard pistons replaced the undersized pistons, and still all was quiet, although one or two diagrams taken shew slight wavy periods at high speeds. | ||