The general technical requirements of a tank locomotive can be found over on tank engine. This node, which is the proper name of the type of locomotive that carried its own fuel (water for steam), will focus on the different types.
The saddle type tank locomotive had a large water tank fitted over the boiler section like a saddle set over the barrel body of the train. This allowed the water to be pre-heated, increasing the efficiency of the locomotive.
The pannier type tank locomotive had two large tanks on each side of the boiler. These were large, typically square front tanks that looked like pannier bags that horses or motorcycles would use to transport items. They did not go all of the way down to the running boards on the side of the train.
The side type tank locomotive looked similar to the pannier style except they extended all the way down to the running platform or running boards. These did hold more water, and they were the most common types of steam locomotives in the United Kingdom.
The well types were small locomotives that had their water stored in tanks underneath the boiler. While this limited the amount of fuel they could carry, it made them stable due to their low center of gravity. These were normally found in short-run industrial areas.
These tank locomotives were common in the United States 4-4-0 series. The tank was fitted at the end of the steam locomotive, putting the drive wheels under tractive weight.
There are other types and combinations cobbled together over the years, but the above are the most common types of steam engines you'll see in movies or at museums.
Iron Noder 2017