Deaerators are things that remove dissolved gasses in water. Dissolved O2 and CO2 in water will result in boiler corrosion.
So I'm wondering how this was done back in the old days of steam trains, roughly 1830 to 1900. Did every water station have it's own deaerator? Did they just use chemical scavengers to remove the O2 and CO2?
Short googling did not yield any special hsitoric feedwater plants for steam trains. This document by Altair states:
As the years passed, more efficient feed water treatments developed, boiler metal surfaces were maintained free from scale, and the problem of oxygen corrosion became more pronounced. This corrosion along with a trend to higher boiler pressures and the resultant increase in the temperature of the boiler water, highlighted the need for more efficient deaeration equipment. Oxygen attack on boiler metal is accelerated with increased temperatures.
In the early 1920's the first open feed water heater was designed to specifically to remove dissolved gases. This initial design was a counter-flow tray deaerator with a re-boiler coil arranged in the storage section, and an internal vent condenser water box.
Sp it appears that the first dearator was built in the 1920s. So how was corrsion prevented before? Water, unless it's fresh rainwater, contains dissolved minerals - water hardness. When boiling, these precipitate and form a scale layer. While one does not want this scale layer - worse thermal conduction, eventually closes pipes etc, it is a somewhat effective corrosion protection. Altair hint at this when they mention that the first dearator was designed after feedwater treaatment became better.
However, this is not conclusive proof that there was no daeration pre-1900. This could be shown by a survey of train yards etc, if these had any deaeration equipment. Dearation equipment would be especially useful when the feedwater source is mostly soft surface water.
ETA: Commentors ask for a source for the claim that scale serves as a corrosion protection. German wikipedia on Kesselstein - Scale - has this to say:
In 19. and 20th century, boilers were mostly operated without water treatment. Scale had to removed mechanically by Kesselklopfer ("Boiler-bangers"), using pointed hammers. The specific heat load of boilers then was lower and the boilers had no critical areas in regard to scale, so this way of operation was possible. Modern boilers with effiencies would be damaged quickly by scale, so feed water treatment is mandated in industry codes.
this scale layer...it is a somewhat effective corrosion protection Any source for this? If true, it's actually really good news for the early steam days. Also, note a teapot on the stove does not suffer oxygen corrosion. Your Altair source says Oxygen attack on boiler metal is accelerated with increased temperatures. However, boiling water is always 100 C (at standard pressure). If you turn up the heat, it simply boils faster without changing temperature. Maybe they're talking about higher steam temperature, but by then there is no hope of deaerating that. The steam will be mixed with air.
I'm not aware of any use of deaerators in the UK at all.
Some of the companies built water treatment plants, but these were intended to reduce the hardness of the water in order to reduce the amount of scale deposited in the boiler and pipework, and were generally not build until the 1930s - heavy buildup of scale in the injectors can reduce the amount of water getting into the boiler, and a heavy buildup on the firebox can act as an insulating layer, which is bad for the firebox itself. Locos were also subject to regualr boiler washouts, again to remove any loose scale etc.
There's more detail on the LMS* society website here
*London, Midland and Scottish Railway, one of the UK "big four" from 1923 to 1948
