A steam locomotive's reverser controls the direction of motion by adjusting the valve gear that determines the timing and direction of steam flow to the pistons. While it may seem intuitive that setting the reverser to its full position would allow the locomotive to achieve maximum speed, there are several factors that limit its speed even under these conditions:
Power and steam supply: Steam locomotives rely on steam generated by a boiler to produce power. The maximum speed is limited by the locomotive's ability to generate and deliver steam at a sufficient rate. Increasing the reverser setting alone does not increase the steam production capacity of the boiler or the ability of the locomotive to deliver power.
Tractive effort: Tractive effort refers to the force the locomotive can exert to move itself and any attached load. The tractive effort is a function of steam pressure, valve timing, and other factors. While increasing the reverser setting may allow more steam to enter the cylinders, the tractive effort will ultimately depend on the locomotive's design and capabilities.
Track conditions: The condition of the track, including its alignment, curves, and gradients, can impose speed restrictions. Running a steam locomotive at high speeds requires tracks that are well-maintained and suited for high-speed operation. If the track is not designed or maintained for high speeds, it can introduce safety risks and limit the locomotive's ability to reach maximum speed.
Mechanical limitations: Steam locomotives have various mechanical limitations that can prevent them from reaching their maximum possible speed. These include factors such as wheel diameter, weight distribution, and the locomotive's overall design. These limitations are inherent to the locomotive's construction and cannot be overcome simply by adjusting the reverser setting.
In summary, the maximum speed of a steam locomotive is determined by a combination of factors, including power generation, tractive effort, track conditions, and mechanical limitations. While adjusting the reverser setting may impact certain aspects of performance, it does not guarantee the locomotive will achieve its maximum possible speed.