J. T. Marshall valve gear

The J. T. Marshall valve gear was a Type of valve gear for steam locomotives that was invented by one man named "James Thompson Marshall".
J. T. Marshall invented and patented several different valve gears but these should not be confused with the "Marshall valve gear" patented by Marshall, Sons & Co. in 1879. At least one of J. T. Marshall's valve gears was a rotary type and the only known application was to the Austrian BBÖ Class 114 locomotive.
The better-known J. T. Marshall gear was a modified Walschaerts valve gear which was first applied to a Great Northern Railway mineral locomotive, no. 743, in 1901 and received a glowing report. Next, it was tried on GNR Class C2 No. 1520 in March 1903. There was no external change visible on the locomotive as a result of this modification. When the valve gear was in use, the motion was derived from two eccentrics, one of which gave lap and lead movement by swinging the link backwards and forwards on its suspension bracket. The other eccentric was set at 90 degrees to the crank and rocked the link by means of a bell crank on the hanging link pin. The position of the radius rod die pin in the link determined the direction of movement and the cutoff. Showing little advantage over the normal Stephenson link valve gear, it was removed from the C2 'Atlantic' in April 1907 to ease maintenance.
A modified version of the gear (for outside drive) was tried on SECR N class no. 1850 in 1933-4 but, again, it was not a great success.
Category:Valve Gear