水位

Maintaining a proper water level in the boiler is critical. This is done by observing the water gauge and adjusting the amount of water in the tank accordingly. The water level should be visible on the water gauge at all times. This range typically shows between 75% and 85% of the boiler height, which is the intended range of operation. Blowdown valve is used to dump water from the boiler, while the injector is used to add more. Having the water level above the gauge leaves less than optimal room for steam to generate in and may overflow to the cylinders, potentially causing major damage. Having the water level below the gauge can be even more catastrophic. If the firebox is sufficiently hot and its top surface (known as “crown sheet”) protrudes above the water level, it can melt, causing the pressurized boiler to explode.

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。

在水位過低的緊急情況下，防止爆炸發生的最後手段之一是將給水器完全打開，對鍋爐注入更多水，並立即將火箱內的煤炭排出，在火箱頂板軟化之前盡可能降低當中溫度。