Steam dome

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A Steam dome is a vessel fitted to the top of the boiler of a steam locomotive. It contains the opening to the main steam pipe and its purpose is to allow this opening to be kept well above the water level in the boiler. This arrangement acts as a simple steam separator and minimises the risk that water will be carried over to the cylinders where it might cause a hydraulic lock - this is also known as priming. A steam dome should not be confused with a sand dome.