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).
Letter comparing the specifications of different thermostat bellows.
| Identifier | ExFiles\Box 156\1\ scan0102 | |
| Date | 20th May 1935 guessed | |
| - 5 - Messrs. Rolls-Royce Limited. (4). To illustrate the point which we made earlier in this letter that the total movement available for a bellows must be greater than the minimum valve lift if the adjustment is going to be of any service, we are giving you particulars regarding the thermostats shown on our drawings, Nos: BGA. 1743C, 1882 and 1982 which were enclosed with our letter of May 16th. As far as these particulars are concerned, the thermostats shown on BGA. 1982 and 3040 are identical. BGA. 1743C. BGA. 1882. BGA.1982. Bellows Diameter................... 1½" 1.5/8" 1.5/8" Number of convolutions............ 12. 9. 15. Free Length........................ 1.7/32" 1" 1.3/4" Solid Length....................... 13/16". 23/32". 1.1/4" Extension above free length........ 5/32" Free Movement...................... 13/32" 7/16". 1/2" Minimum Valve Lift................. 9/32". 9/32". 11/32". Excessive movement available for ad- justment........................... 1/8" 5/32". 5/32" Opening Temperature................ 75º 75º 80º Maximum full open temperature...... 88ºC. 88ºC. 91ºC. Difference between open & full open temperature........................ 13ºC. 13ºC. 11ºC. You will notice that in each case the bellows is arranged to have available a movement approximately 50% greater than the minimum valve lift required. To obtain this result in the case of BGA. 1882 it was necessary to provide for 5/32" extension of the bellows beyond the free length. The bellows has to be specially treated to give this result, and this practice is to be avoided wherever possible. In this particular case limitations of space made it necessary. If by any chance the remarks under Heading 3 cause you to alter your views to the extent of increasing the | ||