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).
Article discussing a new method of quieting exhausts using a 'Servais' silencer.
| Identifier | ExFiles\Box 152\3\ scan0212 | |
| Date | 18th September 1936 | |
| 120 THE ELECTRIC RAILWAY, BUS AND TRAM JOURNAL. September 18th, 1936. SILENCE! A Novel Method of Quieting the Exhaust WE have had brought to our knowledge recently a new type of silencer for motor vehicles which should go far towards damping out some of that noise, which although unpleasant, we have become accustomed to on busy roads. Known as the Servais, this silencer is of the "straight through" type and is applicable to all motor engines from light cars to the largest of the heavy oil engines. It has been recognised for a long time that engine wear, particularly as regards the valves and pistons, is in direct proportion to the amount of back pressure in the exhaust manifold. The Servais silencer, however, owing to the negligible amount of back pressure, reduces engine wear to a minimum. The design of the Servais silencer is based upon scientific facts and principles while its construction internally is such that exhaust pulsations are damped most effectively. It is claimed that sound frequencies can be absorbed over any desired range, due to the special porous filling, which is built up of constantly varying cells around an entirely free central passage, through which the exhaust gases flow without any form of obstruction. The operation of the silencer is such that the cells are free to vibrate within the casing, and by synchronising with the sound vibrations of the exhaust gases they finally absorb them. Among the advantages claimed from the use of this new silencer are reduced fuel consumption on account of the complete absence of back pressure; less carbon deposit as the particles of soot are blown straight through the exhaust system; increased power; cooler running; reduction of maintenance costs; prevention of panel drumming; and a degree of silence which reduces engine noise to practical inaudibility. Various performance tests have been carried out with the Servais silencer on different types of vehicles which bear out the above claims, and at the present time we are informed that models are undergoing extended trials on petrol and heavy oil engined buses in different parts of the country. We understand that the Servais silencer is already in use on many public vehicles, notably on the whole of the City of Westminster's fleet of night-sweepers, and that stringent tests are at present being carried out by the Associated Equipment Company with the view to fitting it on the buses of the London Transport fleet. Brake horse power and back pressure tests recently carried out on a 3 1/2 litre engine with a Servais silencer compared with one of American origin gave the results tabulated at the bottom of this page. The back pressure results compare with figures for the baffle plate type of silencer of 9 lbs. per square inch at 4,000 R.P.M. The new fitting is a product of Servais Services Ltd. of 8, Old Pye Street, Westminster, London, S.W.1., but we are advised that the heavier models for use of buses and commercial vehicles are being handled by Messrs. Trenchard, White & Co., Ltd., of 37 and 38, Fenchurch Street, London, E.C.3. [Image Caption] Sectional view of the Servais silencer, showing the layers of expanded metal and sheet wool. [Table] R.P.M. B.H.P. Back pressure per sq. in. 1. Manfcts. Standard. 2. American Silencer. 3. Servais. 1. 2. 3. 3000 76.0 84.0 88.5 3.7 lbs. 2.5 lbs. 2.0 lbs. 3500 94.0 96.0 100.0 5.4 lbs. 3.2 lbs. 2.6 lbs. 4000 99.5 102.0 106.5 6.7 lbs. 4.3 lbs. 3.4 lbs. 4500 101.5 107.0 112.0 8.1 lbs. 5.3 lbs. 4.3 lbs. | ||