What’s a Crown Sheet?

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A crown sheet is an important part of any steam engine. This sheet can be found on any ship that relies on a boiler or furnace to power an engine, including locomotives and steamships. A well-maintained and properly cared for corona sheet is key to minimizing the risk of injury or death whenever steam engines are used.
The steam used in a steam engine comes from a large boiler located on or near the engine. This boiler consists of a tank filled with water, which turns into steam when heated. Metal fireboxes were often placed right inside the water tank on these engines. Crews could simply shovel wood or coal into the firebox via an opening in the front, while the top, bottom and sides of the box were always completely submerged in water.

The steel panels that make up the hearth are called sheet metal, with the top panel called the crown sheet. A fire inside the box heated these sheets, which then heated the surrounding water to produce steam. As the steam passed through the engine or out of the flues, the water level in the tank dropped. The task of every engineer or worker was to ensure that this water level never dropped below the crown cloth and that the crown cloth was always completely covered with water.

Crews relied on a simple sight glass located on the front of the tank to help them monitor water levels. If the water ever dropped below the level of the cover, crews knew they would have to put out the fire immediately and let the boiler cool. Otherwise, the crown sheet would collapse, resulting in fires or even explosions. In fact, many steamship or steam locomotive disasters can be attributed to water levels falling below the crown sheet.

Some workers believed that the danger could be averted simply by adding water back into the tank to bring the levels back up and submerge the crown cloth again. This relatively cold water entering the tank led to rapid production of steam, which greatly increased the pressure in the boiler. This excessive pressure would strain the crown sheet and typically lead to explosions.

While steam engines are rarely used today, many history buffs attempt to restore old steam locomotives or ships to work. Due to the age and primitive technology used on these machines, users and spectators should be aware of the potential danger associated with these engines. In addition to closely monitoring water levels, operators should have the firebox inspected before use to ensure it is up to the demands of operation.

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