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).
Notes on fuel vapor pressure, air surging in fuel lines, and improvements to the Sprengel pump system.
| Identifier | ExFiles\Box 44\4\ Scan157 | |
| Date | 13th January 1930 guessed | |
| - 2 - NOTES - 1. The vapor pressure of American fuel is about 10 lbs/sq.in. at 100°F.{Mr Friese} Consequently in hot weather the "air" in the air line between the bell in the tank and the liquid in the U tube is 66% fuel vapor. The air in the fuel tank above the fuel is also a rich mixture and this is what is supplied to the system by the "Sprengel" pumps. But for the fact that the volume of air in the bell is equal to 50% of the entire system the variation of reading when cooling off would be enormous. The fuel vapor is heavy and it is believed that it does not rise into the fine air line, but there seems very little safeguard about this and one would certainly expect to find slugs of fuel in the air line occasionally, in either your installation or ours. To prevent surging of air out of the bell the hole (C on your Hobson diagrams) at the bottom of the bell is very small, and K.S. have recently established by trial that only about 5% of the air and vapor supplied by the Sprengel pumps enters the bell, of which not more than 1/3rd is really air, so that the replenishing effect on the road is much less than it should be. Consequently the recovery of correct reading when a car gets under way is much slower than it should be. This is being improved on all their standard instruments by the method shown in SK-378 attached, by which pure air is supplied to the interior of the bell. This has at least ten times the replenishing effect of the present system. 2. The above improved Sprengel pump comprises their best effort to date for ordinary automobile installation. For aeroplaines however, they are standardising the same installation as is used for the fuel oil tanks used with oil burners in dwelling houses. (I have one installed and it appears to work perfectly). Byrd in the Antarctic is actually using common house-gauges for the five wing-tanks, and appears from his account to place absolute reliance on them though of course they are excessively heavy. This installation is also shown in SK-378. This is the form of gauge which K.S. would propose to use on R.R. cars if they had any say in the matter, and if it is decided to continue the use of a hand pump. - continued - | ||