Bagnall–Price valve gear
Bagnall–Price valve gear is a type of steam engine valve gear developed at locomotive manufacturer W.G. Bagnall as an alternative to the more common Walschaerts valve gear. The gear was patented in 1903 by W.G. Bagnall and T. S. Price, the manager of the works.
The valves are driven from an eccentric cam mounted on one of the driving axles and linkage from the crosshead. The driving axle cam drives a rocking shaft that is mounted inside a cylindrical sleeve (known as the rocking shaft bush) above the cylinder. A drop lever and connecting link from the crosshead oscillates the sleeve to control the lap and lead of the cylinder.
Comparison to Walschaerts
W.G. Bagnall claimed that Bagnall–Price valve gear eliminated some of the complexity of the Walschaerts gear, specifically the combination lever and return gear; this in turn meant the externally mounted gear had greater ground clearance which was an advantage in industrial locations where lineside obstructions could damage the gear of passing locomotives.