James Thompson Marshall
Encyclopedia
James Thompson Marshall (d. 1931) was a British
railway and mechanical engineer known for inventing the 'Marshall valve gear
' for steam locomotive use.
-based Steam Plough Company, and later moved to the city's Boyne Engine Works. He invented the "Marshall valve gear", which was first applied to Ivatt C2 class 'Atlantic' No. 1520 for trial purposes 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.
United Kingdom
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railway and mechanical engineer known for inventing the 'Marshall valve gear
Valve gear
The valve gear of a steam engine is the mechanism that operates the inlet and exhaust valves to admit steam into the cylinder and allow exhaust steam to escape, respectively, at the correct points in the cycle...
' for steam locomotive use.
Career and 'Marshall valve gear'
James Marshall began his engineering career at the LeedsLeeds
Leeds is a city and metropolitan borough in West Yorkshire, England. In 2001 Leeds' main urban subdivision had a population of 443,247, while the entire city has a population of 798,800 , making it the 30th-most populous city in the European Union.Leeds is the cultural, financial and commercial...
-based Steam Plough Company, and later moved to the city's Boyne Engine Works. He invented the "Marshall valve gear", which was first applied to Ivatt C2 class 'Atlantic' No. 1520 for trial purposes 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
Eccentric (mechanism)
In mechanical engineering, an eccentric is a circular disk solidly fixed to a rotating axle with its centre offset from that of the axle ....
, 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
Crank (mechanism)
A crank is an arm attached at right angles to a rotating shaft by which reciprocating motion is imparted to or received from the shaft. It is used to change circular into reciprocating motion, or reciprocating into circular motion. The arm may be a bent portion of the shaft, or a separate arm...
and rocked the link by means of a bell crank
Bell crank
A bell crank is a type of crank that changes motion through an angle. The angle can be any angle from 0 to 360 degrees, although 90 degrees and 180 degrees are common....
on the hanging link pin. The position of the radius rod
Radius rod
A radius rod is a suspension member intended to control wheel motion in the longitudinal plane. The link is connected on one end to the wheel carrier or axle, on the other to the chassis or unibody of the vehicle.Radius rods typically are mounted ahead of the wheel...
die pin in the link determined the direction of movement and the cutoff
Cutoff (steam engine)
In a steam engine, cutoff is the point in the piston stroke at which the inlet valve is closed. On a steam locomotive, the cutoff is controlled by the reverser....
. Showing little advantage over the normal Stephenson link valve gear
Stephenson valve gear
The Stephenson valve gear or Stephenson link or shifting link is a simple design of valve gear that was widely used throughout the world for all kinds of steam engine. It is named after Robert Stephenson but was actually invented by his employees....
, it was removed from the C2 'Atlantic' in April 1907 to ease maintenance.