Of course, the valves that control the steam
distribution into the cylinders must also be controlled to allow for speed
changes and direction of travel. This is the valve gear and many weird and
wonderful types have
been developed over the years.
Stephenson's valve gear
The most common valve gear has been Stephenson which can be mounted inside or outside the frames.
A control from the cab is also required to
reverse the motion. This is called the reversing lever (or screw) which also
can adjust how much steam is let into the cylinder (cut off).
Walschaerts valve gear
More modern locomotives use Walschaerts gear.
1
Eccentric Crank (Return Crank)
2
Eccentric Rod
3
Reach Rod
4
Lifting Link
5
Lifting Arm
6
Reverse Arm & Shaft
7
Link (Expansion Link)
8
Radius Bar
9
Crosshead Arm (Drop Link)
10
Valve Stem Guide
11
Union Link (Anchor Link)
12
Combination Lever
13
Valve Stem
The animation below shows how to locomotive is
reversed.
Joy valve gear
Our Lynton and Barnstaple Manning Wardle
locomotives have the much rarer Joy valve gear.
