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 and test results for a Graham Car Supercharger.
| Identifier | ExFiles\Box 140\1\ scan0059 | |
| Date | 23th July 1934 | |
| Hs{Lord Ernest Hives - Chair}/Aln.1/WJ.23.7.34. GRAHAM CAR SUPERCHARGER. DESCRIPTION. This blower is of the centrifugal type comprising a rotor 7.5" in diameter having twelve blades and mounted on a vertical shaft. This is driven through a skew gear of 29/6 ratio from the water pump and dynamo shaft. The total step up is given as 5.76 : 1 of the crankshaft from which we have taken a dynamo speed of 31/26 times crankshaft and run the machine at corresponding speeds to represent the engine speeds as labelled on the curves attached. The rotor is a sand casting in aluminium alloy, machined on the clearance faces, but otherwise left rough except for certain patches on the blade disc which are milled for balancing. There are three .185" holes drilled axially through the blade disc on a 1.925" diameter the object of which appears to be to convey away leakage oil. A noticeable feature of the blower is the absence of a diffuser, the rotor delivering straight into the volute. The tip axial width is only about 0.100". This, as it appears from the tests is quite adequate. The rotor shaft is carried in plain non-floating bushes .655" diameter and the rotor is overhung, a downdraught carburetter being mounted direct on the eye of the casing. This last embodies a water jacket which, however, we did not use on our tests. The blades of the rotor are curved at the inner ends as viewed face on to reduce the shock losses of the entering air. Clearances are rather large, being .045" behind the blade disc and an average of .075" between the blades and the casing. We found we could reduce the latter by .025" by removing the casing joint washer and ran one test with this out to show the improvement made by reducing clearance. TESTS. We tested the blower complete with carburetter with dry air at 1000, 2000, 3000, and 3500 engine RPM. We then made a test with carburetter removed from which an approximate curve of carburetter depression was deduced. The casing joint washer was then removed and another characteristic taken. Finally a curve in standard complete condition was obtained with petrol supplied. All these special tests were done at 3000 RPM. | ||