水位

When running steam engines , it is of utmost importance to maintain a nominal water level in the boiler . This is done by observing a water gauge and adjusting the water level accordingly with available controls. The water level should always be visible in 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, destroying the entire vehicle.

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

To feed water to the boiler from storage , there's an injector . To dump water from the boiler there's a blowdown valve. Both controls are usually found in a vehicle's cab .

水位は熱膨張の影響も受けます。水温が上がると、ボイラーに水を追加していなくても、水位は上昇します。

水位は勾配によっても変化し、また、ボイラー内部でうねります。機関車が坂道を下っている場合、平坦な場所よりも水位が低く見えます。その逆も同様です。