A.C. Hewitt is the author of an engine with a single sliding-sleeve valve that gave more power on the test bench than another classic type engines with mushroom type valves.

-It had triangular-shape ports so that for the working stroke they were closed, or rather, not faced. We do not have more information for this machine at the moment, although there is a photograph of a small cylinder with this system.

“Hewitt engine cylinder” (PiP)