Steam Dome

To prevent heated water from leaving the boiler with the steam, an inverted siphon is inserted through the boiler casing and covered with the steam dome. Water does not compress well (about nine percent) and will damage valves and pistons, so it must be removed from the more-compressible steam. To this siphon is attached the throttle, controlled from the cab through a rod attached to the throttle lever. Because of the easy access at the steam dome to the live steam, manufacturers often mount safety valves and whistles to the steam dome.