As a further consideration for the 'early' use of bypass valves on nonarticulated locomotives, an interesting point is raised in the Feb 1906 issue of Locomotive Fireman's Magazine (p.218) where a simple bypass valve into the steam chamber between the piston valves is used to vent any excessive compression in operation. This because, while a slide valve can lift against its spring or counterpressure and relieve excessive compression, a piston valve cannot, and the bypass valve therefore acts 'relieving the cylinder head and piston from an excessive [compression] pressure that would cause the cylinder head or piston to break.'

This of course is the function of Okadee valves -- but these lose the steam mass they vent, rather than recovering it into the steam chest.