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).
Investigation into intermittent noise on 'M' series Bentley cars, traced to the thermostat valve operation and a proposed solution.
| Identifier | ExFiles\Box 156\2\ scan0085 | |
| Date | 10th May 1938 | |
| To By.. from Rm{William Robotham - Chief Engineer}/Std. c. HS.{Lord Ernest Hives - Chair} c. RHC.{R. H. Coverley - Production Engineer} c. Roy.{Sir Henry Royce} c. MX.{John H Maddocks - Chief Proving Officer} RM{William Robotham - Chief Engineer}/Std.1/MR.10.5.38. 1328 THERMOSTATS FOR M SERIES BENTLEY - FB.3509. As a result of complaints of intermittent occasional noise on experimental B.II cars fitted with the M series Bentley thermostat scheme and also car heaters, we have made some investigations and found that at certain engine speeds (approx. 2500 R.P.M. chiefly) a water hammer effect takes place due to erratic operation of the thermostat valve, i.e. it opens and closes rapidly with considerable hunting. This does not materially effect the control of the water temperature, and the water hammer effect is only perceptible when the car heater fitted acts as a resonator. This rapid movement, however, must effect the life of the bellows from a fatigue point of view, and is therefore undesirable - we think that it is also responsible for the loss of bellows free length after running which has previously been reported, although we have not yet been able to prove this point. We have found that this defect in operation is due to the area of the bellows and area of the valve not being balanced - this lack of balance has been known previously, but as the original B.II thermostats and the one which ran 15,000 on 3.B.IV car were all unbalanced in this way as regards pressure and functioned satisfactorily no change was made for M series cars. We have tried out a unit with this lack of pressure balance overcome by increasing valve seat diameter by .125 and reducing bellows size from 1.750" to 1.500" and find that the trouble then disappears. As Rm.{William Robotham - Chief Engineer} does not consider it advisable to make this change on production until some mileage has been covered on the modified scheme, we recommend that the first 100 M series cars should be built with the thermostat scheme as instructed, but that a change over to the larger valve seat and smaller bellows should be made on the last 100 M series cars, by which time we should have completed sufficient running experimentally. | ||