It was when seeking to power their workshops that Henri came up with the idea of flash steam generation, with a patent applied for on 25 October 1879.

Leon went to Paris to study engineering at the Conservatoire national des arts et métiers, and at the same time he continued to develop the flash steam concept with his brother by post.

"[4] In another obituary "M. Serpollet's name has been for a score of years as well known in the world of the steam motor-car as is that of Marquis de Dion in the region of internal combustion vehicles".

[6] Léon continued to revise and develop the flash steam boiler design changing it from flat plates to tubes, which led to further patents (e.g. CH1038 1889, CH7958 1894, CH12280 1896).

Serpollet then used his flash boiler to create a steam powered tricycle, which was exhibited by Peugeot at the 1889 World's Fair in Paris.

[7] In January 1897 he entertained a deputation from Aberdeen at his depot in Willesden, London, where he displayed a 4-seater Phaeton, and a double-decker steam tramcar for 50 people running on a test track.

In 1906 the Darracq-Serpollet company was formed for the manufacture of steam omnibuses and heavy traction vehicles, with Leon Serpollet as one of the managing directors.

[15][16] Later in 1906 a Darracq-Serpollet omnibus made a demonstration tour of England and Scotland, it attracted great interest, and was reported to do 6 miles on a gallon of paraffin.