Mike, the other descriptions in the thread are very good . I only add some details . Hydrostatic lubricators were intoduced in the late 1870s . An 1878 appliance catalog I saw years ago featured them as a "new innovation" . Lo and behold , Dan Markoff's 1875 "Eureka" has one of these pre-1900 lubricators oiling the valves on this engine . For decades these "displacement" lubricators were good enough to lubricate the valves ,cylinders and a single stage air pump . As engines grew in size ,so did the lubricators . Detroit Manufacturing Co made a 6-feed lubricators (i heard they made a 12-feed), though the most common , Nathan or Hancock models, were three-feed . Eventually ,it was realized that a single hydrostatic lubricator was not going to hold enough oil to lubricate piston valves ,cylinders, flange oilers and cross-compound or two single stage air pumps . Arounf 1920 mechanical lubricators became availvbale . They were usually operated by means of a reciprocating arm off the valver gear link . To stop back pressure from valves and cylinders ,there was a check valve placed in the line . Nearly sall of the negines I worked on had both styles of lubricators ,though the hydrostic oiled only the air compressor . Mechanical lubricators were generally heavy duty -with a unit weighing a lot .Shays ,however, had a much smaller one for lubrication the engine in the cab , ahead of the engineer .