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).
Continuation letter from The S.U. Company discussing pump modifications and experimental results.
| Identifier | ExFiles\Box 149\1\ scan0303 | |
| Date | 12th September 1936 guessed | |
| THE S.U. COMPANY CONTINUATION NO. 2. Messrs. Rolls-Royce Ltd. which is effected by cutting this amount off the legs of the pedestal. This enables the same pump to function on 7½ volts. The shortened stroke does not result in the pump working considerably faster, as we have also changed from the seaweed base diaphragm to the zinc base, which normally makes the pump run somewhat slower as it is stiffer. Thinking this matter over last night, the writer thought it possible that if we were going to reduce the stroke by 20 thou, it would be possible that we might be able to adopt your suggestion and deepen the recess of the armature, eliminating practically the third stage in the pull. This morning therefore, we have been experimenting with the armature 25 thou. deeper in the recess and it appears to be satisfactory. We do not think that this would have proved satisfactory with the old gut diaphragm which was subject to shrinkage, but with the later diaphragms with which this trouble is not experienced, we do not need the build up at the end of the power curve which you recommended previously, should be reduced. Of course, if we can increase the depth in this way, we have two alternatives, either to retain our present 5 thou. impact washer and leave the other 25 thou as an air gap, or else to put a 30 thou. impact washer in. We are experimenting, seeing whether the former is effective under all conditions. It will have the advantage that we do not have to allow for limits in the impact washer, which we believe are about 10 thou. We have built up a standard Bentley pump with the arrangement which you originally suggested of a brass distance piece and 30 thou. impact washer, but here again we have had to cut the stroke down by 20 thou. There is no question however, that the impact washer does silence the pump considerably, and we think it would be acceptable to you. It would however be very much better if we could arrange to obtain this silence by altering the armature, as it appears to be unlikely that we shall be able to make Armatures interchangeable on pumps with the other arrangement; every set would have to be matched up and shimmed. Will you therefore let us know whether you would rather we sent you on the pump as called for, or would -2- | ||