Re: Tank Car Capacities

Dave Parker

Dennis captured the gist of it, but here are a few more details concerning the shell and dome volumes both being listed in the tariffs. 

1.  Starting in 1917, all new general purpose tank cars (MCB/ARA Class II and III, later ICC 103 and 104) had to built with a minimum dome volume of 2% of the total car volume (shell plus dome).  So, a 10,000 gal car needed a dome a bit bigger than 200 gallons.  Allowing for variation in the shell size, many builders used 210 gal domes to achieve this minimum.  But many cars were built with larger domes:  ca. 270 gal (~2.6%) or 340 gal (~3.4%) as but two examples.  Similar patterns can be seen in the tariffs for 8000 gal cars, i.e., 165 was the minimum, but you can find lots of 210- and 265-gal domes.

2.  Based on the 1923 ICC regulations (a revision of the 1918 regs which I don't have), "inflammable" liquids shipped in uninsulated cars had to have adequate room for expansion.  The numerical values of that extra space depended on two things, the expansion coefficient of the particular commodity, and the temperature at which it was loaded.  This was captured in an "outage chart" which allowed for a quick graphical calculation of the needed volume.  For example, gasoline or naptha loaded at 55 F required an expansion volume of ~2.5%, not the 2.0 % offered by the dome of some cars.  But, the same liquid loaded at 75 F could be legally loaded into a car with a 2.0% dome.

3.  Dennis is correct in that, if the dome volume was not adequate, the additional expansion volume could achieved by not filling the car to the very top of the shell (BTW, filling part of all of the dome itself was strictly verboten).  Apparently, this was routinely accomplished by using an outage table that was unique to each car volume and geometry, and supplied by the builder (I have seen a couple).  Each table would show how many gallons of headspace would be gained by filling to 1, 2, 3, 4, etc. inches below level-full.  This strikes me as something of a chore compared to being able to simply top off the shell, and may help explain the apparent popularity of cars with larger domes.

Certainly the tariff books must have been a convenient resource.  Any car rolling into a loading facility could be quickly looked up, and the adequacy of the dome volume for that particular situation (commodity and temperature) immediately assessed.

Of course the tongue-in-cheek answer to Lester's question is that the tariff books exist to facilitate the research of rail-fans and modelers.  The tank and dome volumes are incredibly useful tools for identifying blocks of identical cars and then relating them back to the manufacturer (and sometimes the build year).  Mike Schleigh and I have untangled a large fraction of the Sinclair fleet, in no small part due to the tariffs (Ian, thank you again for your yeoman's effort on these books).

Dave Parker
Riverside, CA

On Friday, November 10, 2017 5:49 AM, "destorzek@... [STMFC]" wrote:


---In STMFC@..., wrote :

I purchased and received in the mail the book titled Tank Car Capacities Tariff, Freight Tariff 300-H, from 1955, showing capacities  of tank cars.  The book was digitized by Ian Cranston and reproduced by Lulu.  The book provides the capacity of a tank car in gallons for the shell and dome.  I do not understand why the gallons would need to be split between the two rather than just the total of the two together.  Does someone know what the purpose of providing numbers for the shell and dome separately was?  Thank You in advance for your time and effort to help.
Lester Breuer

The shell capacity is the actual amount you can ship in the car; the dome capacity allows you to calculate the percentage available for expansion, so you can adjust the amount you load if the expansion is not adequate for your particular commodity.

Dennis Storzek

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