What was this for?

[jacon12]

What was/is the purpose (on the prototype) of the green 'tank-like' object on the top of my 4-6-2 O scale locomotive, right above the headlight?

Thanks,
Jacon

[FThunder11]

All I see is a red "X" in a little box[:(]. I hate thoes litttle red "X" thingys!!!

[Anonymous]

It's a representation of a feedwater heater--a type of heat exchanger which used steam to pre-heat water from the tender before it was pumped into the boiler. Feedwater heaters increased the efficiency of locomotive boilers and reduced the stress on the boiler which could be caused by injecting cold water.

[jacon12]

Thanks Fiverings.
Fthunder11, I hate the red X's too!
Thanks for looking in though..
Jacon