A train reverser works by mechanically adjusting the locomotive's valve gear to change the direction of the steam or air flow to the cylinders, thereby reversing the engine's motion.
Understanding the Train Reverser
The train reverser, also known as a reversing gear or control lever, is a crucial component in steam and some diesel-electric locomotives. Its primary function is to control the direction in which the locomotive travels – either forward or backward.
The Mechanism
Based on mechanical linkages, a train reverser utilizes a lever system to achieve this directional change.
Here's how the mechanism typically operates:
- The Lever: It has a handle and sprung trigger at the top and is pivoted at the bottom to pass between two notched sector plates. This design allows the operator to select specific positions.
- Notched Plates: These plates contain indentations that correspond to different settings, including forward, reverse, and often multiple 'cut-off' positions within forward gear (relevant for steam engines to control efficiency). The sprung trigger on the handle engages with these notches to hold the lever securely in the chosen position.
- The Pivot: The lever rotates around a fixed pivot point, allowing its lower section to move in an arc as the top handle is moved.
- The Reversing Rod: The reversing rod, which connects to the valve gear, is attached to this (handle) lever, either above or below the pivot, in such a position as to give good leverage. This rod transmits the movement of the reverser handle to the valve gear mechanism.
- Valve Gear Connection: The reversing rod is linked to the locomotive's valve gear (like Stephenson, Walschaerts, Baker, etc.). The valve gear is responsible for controlling the timing and duration of steam or air admission to the engine's cylinders.
| Component | Function |
|---|---|
| Handle & Trigger | Operator interface, locks position |
| Pivot | Allows lever rotation |
| Notched Sector Plates | Provides discrete positions (Forward, Reverse, Cut-off) |
| Reversing Rod | Connects lever to valve gear |
| Valve Gear | Controls steam/air flow to cylinders |
How It Changes Direction
Moving the reverser handle fundamentally alters the configuration of the valve gear.
- Forward: When the reverser is set to 'Forward', the valve gear is arranged to admit steam/air to the cylinders in a sequence that pushes the pistons and thus the wheels in the forward direction.
- Reverse: When the reverser is moved to 'Reverse', the geometry of the valve gear linkage is flipped. This causes the valves to open and close at precisely the opposite times relative to the piston's position. The steam/air is now admitted in a sequence that pushes the pistons in the opposite direction, causing the wheels and train to move backward.
- Mid-Gear: A 'mid-gear' position often exists where the valve gear is set so that minimal or no steam/air is admitted, effectively disengaging the engine from the cylinders.
The physical movement of the lever translates through the reversing rod to complex linkages in the valve gear, shifting their relative positions to change the engine's operational direction.
For more information on locomotive components, you might refer to technical diagrams or historical railway publications (e.g., a link to a hypothetical resource like Railway Technical Details).
