The three dome tank car has been a model train tradition for more than half a century. Far more common on our rails than the prototype, the cars are not without authenticity however. Nor were one and three domes the only options.
Three Cars in One
The dome on a tank car serves two purposes. first, it includes the hatch through which product can be loaded and second, it provides an area for expansion should the contents experience an increase in temperature during transit. This is important, because a tank car needs to be filled nearly completely for transit. If not, the waves caused by liquids sloshing about within the car could easily cause a derailment.
Three dome tank cars actually have three tanks on the same frame. Each tank section has its own dome. This gives the shipper several options when using the car. Like a single dome car however, the tanks would need a thorough cleaning before being reloaded with any other commodity.
Each compartment could be loaded with a different product. If there were differences, most commonly it would be a different grade of the same commodity.
But the separate tanks also gave the shipper more control over the volume of shipments by only filling one or two of the compartments. Even a partial fill in one of the tanks would be much less likely to cause problems due to the limited volume.
What did they carry? Three (and more) dome cars have been used from everything from oil to wine. So when it comes to spotting a car on your layout, let your imagination be your guide!
Where did they go?
Although they are exceptionally rare today, multi-compartment tank cars still roam the rails. Changes in tank car design have largely eliminated the need for an expansion dome as we knew them on the older cars. This makes spotting these compartmentalized tanks even more challenging.
A bigger factor in the demise of this type of car came from trucks. With road delivery a more efficient and affordable option for small shippers, the customers for the small cars disappeared. Like “Less than Carload” boxcars, the multi-dome tank vanished when shippers only needed full-carload service.
Several of the older cars have been preserved in railroad museums and on operating short lines all across the country. And of course, we can keep the tradition alive on our model railroads as well!