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 Zenith Carburetter Co. detailing the procedure for measuring air flow through a carburetter using orifices and a draught gauge.
| Identifier | ExFiles\Box 122\4\ scan0157 | |
| Date | 15th June 1938 | |
| THE ZENITH CARBURETTER CO. Limited. Sheet No. 3 Messrs. Rolls-Royce Ltd. 15/6/38 valve between the pump and the main regulating valve. Its dimensions will depend upon the quantity of air per minute which you wish to pass through the carburetter. The draught gauge may be obtained from Messrs. Geo. Kent of Luton, although in our own case we made this up ourselves. We find it convenient to add hereto the recommended practice of using a pressure drop not more than about 2" of water across the orifice, and the draught gauge should be of such dimensions as to accommodate such a pressure drop. We use orifices from 1/8" in diameter up to 2" in diameter, and should the air flow exceed that given by the 2" orifice with a pressure difference across its faces of more than 2" water, then we multiply the number of orifices. The reasons for this are that very little accurate work has been done on sharp edged orifices over 2" in diameter and at a pressure difference exceeding 2" water. We attach to this letter a table showing the lbs. of air per minute given by orifices of 1/8" 1" 1.5" and 2" in diameter, with a pressure difference of 1" of water and at a barometric pressure of 760 m/m of mercury and a temperature of 15º C. You might find it convenient (as we have done) to use white spirit when measuring the pressure difference, instead of water, in which case then it is only necessary to correct for the specific gravity of the white spirit, the reason for using which is that evaporation of the white spirit is much slower and the maniscus is much more clearly defined. If extreme accuracy is required, corrections ought to be made for variations in barometric height, in temperature, and for pressure drop across the orifice, and we are adding a schedule giving the various corrections, although we think you will find that they are not of very much moment outside an academic interest. The petrol supplied to the carburetter is controlled through a float chamber under filter, and is measured by means of graduated bottles, or by means of a graduated burette, which may be obtained from any chemical supplier, or (as in our own case) from Messrs. Beeker Ltd., Hatton Garden, E.C.1., and Messrs. Jas. Powell & Sons (Whitefriars) Ltd., 100, Wigmore St.{Capt. P. R. Strong} W.1. You will probably query on the arrangement drawing | ||