Feedwater Heater - A feedwater heater is a small, unfired pressure vessel that uses exhaust steam to preheat incoming feedwater, maximizing efficiency be making use of the waste heat in the steam. These are typically either a steam chamber within the engine frame that a water pipe passes through, or a separate tank with either water or steam passages. The feedwater heater typically was connected to a pump rather than an injector, as the water expands as it heats, and could run backwards through an injector.
    Like most parts of a boiler, a feedwater heater is subject to sediment, and needs to be flushed out regularly. Most are equipped with drain cocks, and the one that drains the steam section should generally be left open, otherwise the exhaust line will tend to accumulate condensed steam when the engine sits idle, spraying it all over you and any bystanders when you start the engine turning again.