In a discussion about the Chamberlain 8 a reference was made that it had a German "Berk" supercharger , after bit of googling from "Berk" appears to be english
https://www.motorspo...f-supercharging,
it appears to have been made by "Messrs. PressureVac, Ltd., North Parade, Bradford, Yorks" and the article also states that A.E. Waite's record braking Austin 7 was equiped with one as was Major Halfords A.M. Special
returning back to the Chamberlain i have seen a sketch of the rotors in the blower ,and they are of the 3 lobe variety, as the Chamberlain engine dates from the early 1930's
i was surprised , from the above article "As regards the actual design of the "Berk" Superchargers, those are of the well-known Roots-Blower type, having a patent for of three-arm rotor," the article was from 1926 , i had thought that 3 Lobe rotors were General Motors development for the -71 series diesels of the late 1930's
Its interesting at the end of the article states that a smaller Supercharger would soon be available for motorcycles
I have had no luck finding the patent of the three-arm rotor, and wonder what became of "PressureVac Ltd" or would any one know of other vehicles fitted with their products, and is any one aware of an earlier Roots type supercharger with 3 lobe rotors