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).
The M. series Bentley thermostat unit, discussing material changes and testing.
| Identifier | ExFiles\Box 156\2\ scan0053 | |
| Date | 31th March 1938 | |
| 1328 To By.{R.W. Bailey - Chief Engineer} from Rm{William Robotham - Chief Engineer}/Std. c. Hs.{Lord Ernest Hives - Chair} c. Da.{Bernard Day - Chassis Design} c. Roy.{Sir Henry Royce} Rm{William Robotham - Chief Engineer}/Std.1/AP.31.3.38 M.{Mr Moon / Mr Moore} series Bentley thermostat unit - EB.3509 We have completed 500 miles running on a thermostat unit to EB.3509 as per M series production which had been definitely checked by the makers, The British Thermostat Co.Ltd., as being correct (within .015) for free length before sealing, so that if the charge was let out it would assume a 'valve full open' position. Measurement of the bellows unit after this mileage, with the charge released, indicated a reduction in free length of approx .040 according to the makers measurements, but .095 according to ours. This alteration has not made any appreciable difference to the running temperature. We are accordingly checking this over on another thermostat unit, but meanwhile the makers recommend that the bellows should be made in 'Alumbro' instead of 80/20 brass as this material has a higher tensile strength and is less subject to fatigue. Since the only disadvantages of this material are (1) that it is more expensive - however the makers will make no charge for the change of material, (2) That it will slightly increase the range of temperature control of the unit - this is not important, we recommend that the production bellows are made from this material and have accordingly instructed the makers to produce the first 30 or 40 from it. This material is used for thermostats by the British Thermostat Co.Ltd for our aero engines. Meanwhile we are testing a thermostat made from this material for reduction of free length under running conditions. The better material should also reduce the likelihood of a failure occurring + it must be remembered that this difficulty of reduction of bellows free length is only of serious importance if and when the bellows fails. Rm{William Robotham - Chief Engineer}/Std. | ||