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).
The 'Maximum Pressure Indicator' apparatus for measuring pressure in engine cylinders.
| Identifier | ExFiles\Box 165\4\ img144 | |
| Date | 9th March 1932 | |
| X4580. Rg.{Mr Rowledge} From Hs{Lord Ernest Hives - Chair}/Yag. c. to Mr. KP. c. to Mr. By.{R.W. Bailey - Chief Engineer} c. to Mr. Jaques. Hs{Lord Ernest Hives - Chair}/Yag.3/MA.9. 3. 32. X2965. MAXIMUM PRESSURE INDICATOR. A set of tackle has been made up for measuring maximum pressure in engine cylinders. This employs the Dobbie McInnes 'Farnboro' electric pressure gauge and disc valve unit. The attached photograph illustrates the complete apparatus rigged up on the Kestrel Single Cylinder unit and shews the arrangement of the various units. Sketch A shews a section of the 'Farnboro' disc valve unit and sketch B gives a diagram of the electrical connections and the air pressure line. The 'Farnboro' electric pressure gauge is merely an ordinary pressure gauge having an insulated metal strip running round the edge of the dial. This strip is connected to an external terminal. In principle the working of the apparatus is simple. Air pressure is led from the air bottle into a distribution box which has leads to the disc valve and to the electrical pressure gauge. As regards the electrical circuit. A 6 or 12 volt battery supplies current to the primary winding of an induction coil and the disc valve is connected in series in this circuit. One terminal of the secondary winding is connected to the insulated strip of the pressure gauge whilst the other is earthed. When a maximum pressure reading is to be taken the air bottle pressure is turned on and the gauge run up to a pressure in excess of that which is expected in the cylinder. The air supply is then shut off, the primary circuit closed and the cock on the disc valve turned on so that the 'back' of the disc is exposed to the cylinder pressure. Air is then slowly released from a cock on the distribution box. When the cylinder pressure slightly exceeds the pressure in the air line the disc will be pushed off one seat of the valve body to the other. As expansion takes place in the cylinder and the pressure in the air line exceeds the cylinder pressure the disc will be transferred to its former seat. | ||