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).
Recommendations for the installation and operation of a 'General' Bye Pass Oil Filter.
| Identifier | ExFiles\Box 140\3\ scan0172 | |
| Date | 13th June 1938 | |
| 1139 "GENERAL" BYE PASS OIL FILTER. The above is a product of J.B.Webb Co., 8951 Alpine Avenue, Detroit, Michigan, and we give herewith the recommendations of our experience for its installation. It is about to be produced in this country. The pressure on the inlet to the filter is taken from the main bearing pressure, up to 50 lbs/sq.in. maximum, the actual pressure, of course, varying with the engine speed and the oil viscosity. Our normal pressure is around 30 lbs/sq.in. As you are probably aware we have a two stage relief valve, high pressure for the main bearings and low pressure for the valve gear etc. and feed into the filter from the main pressure and oil return from the filter into the low pressure (approx. 4 lbs/sq.in.) thus there is an effective pressure drop across the filter of 30 - 4 = 26 lbs./sq" with which arrangement the filter gives very satisfactory results. The reason we return to the low pressure from the filter and not freely back to the sump oil is as follows. When the engine is idling at a very low speed with hot oil, the pump flow is insufficient to give a main pressure reading of higher than approx. 5 lbs/sq.in. and if a free flow back to the sump were taken through the filter from the main pressure, a valuable quantity of oil would be lost and serving no useful purpose, also the main pressure would drop almost to zero. By returning the oil from the filter to the low pressure the valve gear etc. gets some lubrication which otherwise would be starved. The inlet pipe to the filter should not be larger than ¼ dia. and the outlet from the filter not less than 5/16 dia. Most people appear to mount the filter from the dash and use flexible pipes to the engine but we fix the filter to the engine and use copper pipes, the alternative being immaterial and according to which condition is most applicable. | ||