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Message: <blockquote data-quote="Sandpatch" data-source="post: 190264" data-attributes="member: 10543"><p>The backhead shot at Promontory is great -- so much color and detail! I think the three valves arranged diagonally are to check the water level in the boiler, a VERY important check to avoid a boiler explosion. Steam locomotives also had water level sight glasses for this function, but they could plug and show a false indication, so the valves were worked on occasion to assure safety. The device below them captures the hot water when they're opened. Boilers were equipped with safety valves too, but if a boiler were to run low on water and expose the crownsheet, the steam within the boiler would expand at such a rapid rate as to rupture the boiler before the safety valves could lift.</p></blockquote><p></p>