Something I have meant to ask for awhile:

What purpose did the tank car dome serve? Tank cars used to have domes. Now they basically have a valve and fitting. What changed technologically that they now are dome-less? I have guessed that the dome was for air space to allow for expansion/contraction, but not sure if I am correct.

I am not an expert in these matters........so.
I believe that many technologies combined to eliminate some domes. Tank bodies are no longer riveted, loading, and unloading facilities have improved, some tanks are insulated, so heat or cold, have less effect on the tanks contents.
The evolution ( there's that evil word again ) process has been slow, domes have been changing over time, and are either much smaller now, or gone completely, as the need for them changed.
The choice of tank cars can run from all domed cars, to dome-less cars depending on what era is modeled, and what product the car is designed to carry.......yeah, another "rivet" to count, and more research to do.
Fortunately, I don't dislike doing the research.

RESEARCH; n; v; The act of finding information; The dominant excuse for procrastinating.

Kevin,The dome house the loading port and valves.

Tank cars still have domes, they are just smaller or shaped differently. Cars used for hauling compressed gases do not have domes. I am unsure of what determines if a liquid carrying tank car has a dome.

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