水位

When running steam engines , the most critical responsibility is to maintain a nominal level of water in the boiler . This is done by observing a water gauge and adjusting the water level accordingly. The water level should always be visible within the water gauge, typically ranging between 75% and 85% of the boiler height.

If water rises above the limit, there are two potential dangers - there is less room for steam to be generated in, and water can overflow into the cylinders , potentially causing them to break .

If water falls under the limit, the boiler can explode and cause catastrophic damage . If the firebox is sufficiently hot and its top surface, known as “crown sheet”, protrudes above the water level, it can soften from high temperatures and pressure, and lead to the boiler explosion.

In an emergency attempt to save the engine from explosion, immediately feed water and dump coal from the firebox.

Water is fed to the boiler from storage using an injector . It is dumped from the boiler using a blowdown valve, usually found in a vehicle's cab .

水位會受溫度影響。當水溫上升，縱使未對鍋爐注水，水位也會因熱漲冷縮升高。

水位也受坡度影響。若機車正在下坡，水位計所顯示的水位將低於實際水量，上坡時則高於實際水量。