Joy valve gear
Joy valve gear is a type of steam locomotive valve gear, designed by David Joy (3 March 1825 – 1903), Locomotive and Marine engineer, and patented (no. 929) on 8 March 1879. The British patent has not been found but the US patent (US252224 of 10 January 1882) has. Joy's gear is similar to Hackworth valve gear but has a compensating mechanism which corrects for "the slight inequality in the motion of the valve arising from the arc of the lever".
The drawing (right) shows the Joy gear as applied to a London and North Western Railway locomotive. The US patent shows several modifications of the gear. In figure 6 of the patent, one of the levers has been replaced by a slide.
On 10 January 1882, Mr. Joy received U.S. Patent No. 252,224 for the invention.