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).
Calibration and road test report for a Hobson K-S telegage on a 20 HP chassis.
| Identifier | ExFiles\Box 44\3\ Scan091 | |
| Date | 30th November 1928 | |
| Hs{Lord Ernest Hives - Chair}/AJLL/LG30.11.28. HOBSON K-S TELEGAGE. The latest telegage (K-S.155) calibrated for the 20 HP. chassis and fitted to 10-G-111 car has been tested as follows :- Calibration. After fitting up the unit, the petrol tank was filled up with petrol (Shell Mex) gallon by gallon - the petrol gauge reading was noted for each gallon added. The gauge was found to read 1/3 gall. low all the way up the scale. After standing all night with 14 galls. of petrol in the tank, there was no drop in the reading. In order to try and produce summer conditions, 5 galls. of light spirit (80% Swan spirit and 20% Benzol) was put in the rear tank - the tank being kept warm by backing the car up to a radiator; no over-night loss of reading was recorded i.e., if any vaporisation or condensation occurred in the bell, it was not sufficient to alter the gauge reading. Road Tests. The two connecting pipes were disconnected from the tank unit, the tank being full of petrol, and the liquid in the gauge was allowed to drop to zero. The pipes were re-connected and the car driven on the road - a mileage of 55 miles was completed before a maximum gauge reading was obtained, after 35 miles 1 1/3 galls. was registered, after this point more rapid advance was made, the correct reading being registered after a further 20 miles running. The time taken before the correct reading is reached is found to be dependent on two things - viz : the type of road over which the car is run (on a good road the rate of increase in reading is less than on a bad road), and most important - the amount of petrol in the rear tank. In the first road test the petrol tank at the start was full, it was noticed that after the first 35 miles only 1 1/3 galls. was registered, the petrol level in the tank having fallen to about half way between the top and the second cup on the petrol tank gauge unit, after this the reading increased much more rapidly. The inference is that the top cup is placed too high in the tank to allow the swirling petrol to splash into it in any quantity, and it is not until the second cup comes into operation that a reasonably fast increase is attained. On the other hand, if the top cup were placed lower down, more petrol would have to be used before it could come into operation and thus again a considerable mileage would be covered before the gauge shewed any increase. contd :- | ||