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).
Issues and solutions for fuel gauges, balance lines, and tank units on various car models.
| Identifier | ExFiles\Box 19\3\ Scan380 | |
| Date | 19th May 1930 | |
| (England cannot use the central vent in any case because gas tank is built level with top of frame). The balance pipe used on English cars replaces the vent pipe and serves principally to prevent all spilling. Differences in pressure between gas tank and gauge are negligible on our cars. (On cars with tank under bonnet, however, the balance line is necessary for correcting pressure differences). (5) The balance line has caused trouble - now overcome. The tube was sealed to the top of the glass-tube, making it impossible to clean the tube. Also, slugs of liquid spilt over into the balance line in handling the gauge, upset the readings of the gauge. Now overcome by a gland-joint at the top of the glass tube, similar to the K.S. rubber gland used on the oil gauge, but rather better and not causing projection at top of gauge. (6) Another trouble with the English instrument has been defective joint at bottom of glass tube. The copper deposited soldered joint that we used was never used here. But, Hobson now have the fused-in joint which we have had recently, and Expl. Dept. here have now approved it. (7) England object to the short scale that we use, because it will not satisfy continental "octroi" authorities. Hence the long scale. Unfortunately this has been associated with a short "back leg" (to prevent projection below board) and with little excess-length of glass tube above full tank level. This gives little safety factor above full tank conditions to take care of surging, or of a tank full of .680 Benzol instead of .740 petrol. On the long back leg used on our K.S. instruments the lower part of the bore can be of small diameter and is only used in emergencies, such as above, to give sufficient difference in U-tube level without overflowing the glass. (The gauge reads 20% high with straight benzol). (8) On P.II accuracy and visibility of the gauge are more important because small reserve supply of fuel in emergency tank is only sufficient for 6 miles. (9) Returning to our K.S. tank unit. The surge of the fuel column in the vent pipe actually draws air from the Sprengel pump outlets through the small hole in the bottom plate of the bell. On the English tank units lacking the vent pipe, it is necessary to provide a 3/16" air entry hole in the bottom of the bell, in order to encourage the air bubbles from the Sprengels to enter the bell. Also to provide a small hole in the bottom to let the fuel escape. cont'd.{John DeLooze - Company Secretary} | ||