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 from The British Thermostat Co. Ltd. discussing a failed thermostatic unit and proposed solutions.
| Identifier | ExFiles\Box 156\2\ scan0029 | |
| Date | 15th February 1938 | |
| COPY OF LETTER FROM THE BRITISH THERMOSTAT CO.LTD., 15th February 1938. Messrs Rolls-Royce Limited, DERBY. Dear Sirs, We acknowledge receipt of your letter of February 11th. We have examined the Thermostatic Unit EB.3509 which has failed. The shape of the bellows and the fact that there appears to have been considerable 'chatter' between the top bellows plate and the by-pass seating suggests that the bellows failure has been caused by vibration set up due to the fact that the water enters the thermostat casing sideays and impinges directly on the bellows. We had similar trouble with Thermostats supplied to Messrs. Dennis Brothers, and this was overcome by introducing a shield the same width as the diameter of the bellows and interposed between the bellows and water entry. It should, we think, be a comparatively simple matter to utilise a similar shield in your case, and we are enclosing Sketch No. (to follow) showing what we think would be most suitable. With regard to the loss of bellows length which you have observed, although you did not specifically state on your drawing that the free length of the bellows had to be such that in the event of failure of the thermostatic element the radiator valve would open fully, our Drawing did specify this, and there is no doubt that as originally delivered the bellows was correct in this respect. In view of your experience with the standard Vauxhall Thermostat, modified to give perfect balance, it seems probable that the total pressure within the system has been responsible for this loss of length by deforming the relatively light walls of the bellows. We are therefore making up a unit using similar bellows, and we will subject this to a 20 lbs/sq.in. pressure test for 24 hours to ascertain whether or not loss of length does take place. At the same time we are making up an experimental unit with bellows having wall thickness of .007", and if we can get satisfactory temperature operation we will test this bellows with an external pressure of 20 lbs/sq.inch to ascertain whether it is strong enough to resist this pressure without loss of length. As soon as the tests are completed, we will write you again. Yours truly, The British Thermostat Co. Ltd. | ||