Understanding the Reversing Lever on a Steam Locomotive

The reversing lever is a vital piece of equipment found in the engine's cab of a steam locomotive. It is responsible for setting the position of the valve gear, allowing the locomotive to move in either forward or reverse directions. This lever moves from a full forward gear position to various settings through to the mid gear, which is akin to neutral in a car. This mid gear position neither moves the locomotive forward nor backward but serves as a crucial part of the operation.

Reversing Lever Types

There are typically two types of reversing levers:

Lever Reverser: This type of reversing lever has notches for setting specific gear positions. Users can switch gears by moving the lever to different notches, allowing for precise control of the locomotive's direction and speed. Screw Reverser: This alternative provides finer settings due to its screw mechanism. It allows for more nuanced adjustments and is often preferred in highly intricate applications where precise control is paramount.

Both types of reversing levers serve the primary function of reversing the engine's rotational direction. However, their designs also contribute to more than just reversing the direction. They offer stepless cutoff control, which is vital for optimal locomotive performance and economy.

Valve Gear and Cutoff Control

On a steam locomotive, the reversing lever is intricately linked to the valve gear, which controls the flow of steam to the engine's pistons. Proper cutoff control is achieved by fine-tuning the timing of steam delivery to the pistons. This is done by adjusting the timing of the steam's entry into the cylinder based on the piston's position during its back-and-forth travel.

In a well-designed radial gear system, the reversing lever, along with the valve gear, provides stepless cutoff control. This is particularly important for achieving the most efficient and economical operation of the locomotive. The process involves opening the throttle completely as early as possible and then making fine adjustments to the cutoff to match the power output to the train's resistance.

Multiple Functions and Controls

The reversing lever also has a neutral position, and on some diesel locomotives, it has an additional off position. Access to these positions requires a special key to unlock the controls, adding an additional layer of safety and management.

Function: The reversing lever effectively controls the locomotive's direction. It can also control the amount of steam delivered to the pistons and the timing of steam delivery, which in turn affects the thrust and speed of the locomotive.

Valve Adjustments: By adjusting the valves, the reversing lever allows for more economical use of steam. Proper settings can enhance the performance and efficiency of the engine.

Johnson Bar Example: In the United States, the reversing lever is often referred to as a Johnson Bar. It is a lever that controls how steam is delivered to the piston arrangement on the locomotive. It can control both the amount and timing of steam, making it essential for precise control and operation.

For a better understanding of how this works, you can refer to several animations that demonstrate different arrangements of valve gear and steam flow. The Nevada State Railroad Museum in Carson City has a great interpretive panel that describes the steam flow for their locomotive, Inyo. These resources provide a clearer visualization and explanation of the process.

Overall, the reversing lever is a critical component of a steam locomotive, combining functions that ensure the locomotive's efficient and safe operation. Its design and operation are based on centuries of engineering expertise and continue to be relevant in the study and preservation of historical steam locomotine technology.