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).
Internal memorandum comparing the performance and longevity of their filter design against American competitor filters.
| Identifier | ExFiles\Box 135\3\ scan0210 | |
| Date | 5th January 1938 | |
| S. SMITH & SONS (MOTOR ACCESSORIES) LTD. CRICKLEWOOD WORKS. Memorandum for inter-house correspondence only. To: MR. NICHOLS From: MR. GROSE Date: 5/1/38 Re: GENERAL FILTERS. I have read Mr. Robotham's letter and the correspondence with America in connection with the above Filter and can assure you that this type of Filter is no different from the Fram or Briggs type. It is the usual American Filter employing a cylindrical core of material, such as Fuller's Earth, which although capable of delivering clean oil, nevertheless has nothing like the life ours has. I presume it is for this reason they make it si easily detachable, as they have to replace it fairly frequently. Mr. Robotham will readily appreciate that the life of a Filter must depend on its surface area and that it is only with our design of Filter one can obtain a large surface area in such a small space and, of course, a long life. If Mr. Robotham is content for a Rolls-Royce owner to have to frequently replace his Filter element, say every 3,000 or 4,000 miles, then, of course, there is nothing more to be said, but it is our view that the owner would much prefer to have a slightly more expensive Filter which might give 15,000 or even 20,000 miles. May I give you an example of the difference - A Cylindrical core type of Filter of similar outside dimensions as our Filter would have a total surface area of approximately ¾ sq.ft. ours on the other hand has 11 sq.ft. nearly fifteen times greater surface area. Therefore, you will see what a wonderful claim we have over and above the American design and for this reason we have no difficulty provided the Filter is the correct size for the engine in getting an average of 15,000 miles of service from one Filter. In fact, we have had cases where an engine would run for 23,000 miles before needing a replacement. contd: | ||