The speed of Steam locomotive is controlled by regulating steam flow to the engine.
In a steam locomotive, the steam flow to the engine is controlled by adjusting the throttle valve.
The throttle valve regulates the amount of steam entering the cylinders of the steam engine, which in turn controls the power output and speed of the locomotive.
The locomotive engineer adjusts the throttle valve to achieve the desired speed and power output.
The throttle is typically controlled by a lever or a wheel located in the locomotive cab.
The engineer can increase or decrease the throttle setting to accelerate or decelerate the locomotive.
In addition to the throttle, steam locomotives may also have other control mechanisms to regulate speed, such as the reversing lever, which controls the direction of travel, and the brake lever, which controls the application of the brakes.