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).
Technical explanation of Hermiss Spark Plug Adaptors and their principle of operation.
| Identifier | ExFiles\Box 162\3\ img124 | |
| Date | 19th June 1938 guessed | |
| For file. Re Hermiss Spark Plug Adaptors The above adaptors consist, in general, of an insulated tube, in which is incorporated a small air gap. This gap acts as an auxiliary gap in the plug to distributor circuit. The principle under which these adaptors work, is that by inserting a small gap in the plug circuit, the voltage of the latter must build up sufficiently to jump this gap, even if the plug points are partially shorted by oil or water: the resultant energy at the plug point will tend to clear the short. Whereas, without such a gap, the short would tend to prevent the secondary voltage from building up. However, as we already have such a gap in our distributor, and there must be a certain voltage drop across such gaps, we do not consider the inclusion of an additional gap worthy of consideration. In order to obtain a figure of merit for these adaptors, a set was handed to RM{William Robotham - Chief Engineer}/STD, whose "Rover" is known to suffer from beads of water forming on the plug points overnight. Herewith a copy of his report. | ||