Double beat valve

[1] His valve is in the form of a hollow cylinder provided with two seats of nearly equal diameter, at A and B in the diagram.

In Hornblower's valve, the steam flows past seat B only.

[2] The Cornish valve gear, as used on early beam engines, was invented by Murdock, an assistant of James Watt, in 1820.

[4] The Lentz gear, of German origin, was first applied in Germany in 1899 where it became widespread, and was subsequently also manufactured in the United States.

[4]: 113–14  The Putnam engine, a high pressure variable cut-off steam engine built by Putnam Machinery Co. in the United States, featured four double beat poppet valves operated from a single camshaft.