 They subsequently fell from use due to advances in poppet-valve technology, including sodium cooling, and the Knight system double sleeve engine's tendency to burn a lot of lubricating oil or to seize due to lack of it.The Scottish Argyll company used its own, much simpler and more efficient, single sleeve system (Burt-McCollum) in its cars, a system which, after extensive development, saw substantial use in British aircraft engines of the 1940s, such as the Napier Sabre, Bristol Hercules, Centaurus, and the promising but never mass-produced Rolls-Royce Crecy, only to be supplanted by the jet engines.A sleeve valve takes the form of one or more machined sleeves.