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).
Description of the working principle of the Hobson Petrol Gauge.
| Identifier | ExFiles\Box 44\4\ Scan181 | |
| Date | 17th May 1929 guessed | |
| HOBSON PETROL GAUGE. This gauge indicates the amount of petrol contained in the tank by balancing the head of petrol in the tank against a column of dense liquid on the dashboard. The pressure set up by the head of petrol in the tank is transmitted to the column of liquid on the dashboard by means of a column of air in a small bore tube. The type of Hobson petrol gauge which has been developed for R.R. cars consists essentially of 3 units : (1) A 'U' tube on the dashboard containing a very dense fluid known as Tetra Ethyl Bromide. (2) A tank unit consisting of a top casting which fits on to a flange on the tank and which carries three tubes which reach to the bottom of the tank, to the lower extremity of which is attached an air bell. At various distances between the top and bottom of these tubes are fitted small cups. As the petrol surges about in the tank air is trapped in these cups and conveyed to the bell at the bottom of the tank. When the bell is full of air the head of petrol in the tank exerts a pressure on the air bell which pressure is conveyed by means of the fine bore tube to the dash unit, which lifts one leg of the liquid in the 'U' tube which rises to different heights according to the amount of fuel in the tank, and so records the amount of fuel available. In order to get a well damped reading when the car is travelling along the road, contd :- | ||