Geared steam locomotive
A geared steam locomotive is a type of steam locomotive which uses gearing, usually reduction gearing, in the drivetrain, as opposed to the common directly driven design.
Piston valve (steam engine)
The usual locomotive valve gears such as Stephenson, Walschaerts, and Baker valve gear, can be used with either slide valves or piston valves. Where poppet valves are used, a different gear, such as Caprotti valve gear may be used, though standard gears as mentioned above were used as well, by Chapelon and others.