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。

緊急時には、最後の手段の一つとして、内火室天井版が溶ける前に温度を下げることを目的に、注水器をほぼ全開にして大量の水を追加し、火室から石炭を排出することが挙げられます。