If I remember my physics correctly, when you have two tanks connected by a pipe (or hose) the water in both tanks will equalize in height. If one tank is smaller than the other, the water would just overflow out of the smaller tank until the water level in both tanks is the same. Assuming I remember my physics correctly, I have a question.

How did railroads (or current operators) keep water from overflowing in auxiliary cars? If my physics is correct, it seems like the aux tank would start overflowing before the engine tender was full.

Of course, if my physics are all wrong then please feel free to correct me. Thanks.

Check valve, possibly with a bypass circuit so you could fill both tenders at once but once the bypass was closed it wouldn't overfill the smaller one?

Seems easy, but I've never worked with an auxilliary tender...

Steve Hunter
Cardinal, Ontario

On the 261 's tender there is a check valve installed in the inlet pipe which allows us to fill the tender to its full 20,000 gallons, and not have it backflow into the auxiliary tender, the top of which is several inches lower than the locomotive tender. Your physics is correct.. if the check valve was not there then the top thousand gallons in 261's tender would run out the auxiliary tender's fillers until they were equalized. We ran the first couple years without the check valve and during that span of time we filled both tenders seperately and simply would not cut in the aux tender till the first service stop to prevent the overflow issue.

By "smaller", do you mean "shorter", or "fewer gallons"? I think the response will be different depending on the definition of "smaller".

In my response I am assuming the only difference that matters is the maximum height of the two tenders. Also, before anybody asks, assuming that any air space in both tanks is at atmospheric pressure only!

Any difference in volume will be irrelevant, if the top of both tanks (as in the hatch) are at the same height.

Steve Hunter
Cardinal, Ontario

WT51 at TVRM is taller than 610's tank so would indeed overflow it if not cut-out when both were topped off. As Mr. Selinsky notes, we just cut it in at the first convenient location - usually at Chickamauga on the Summerville runs - by then we had used more than enough water climbing Missionary Ridge for the water level to equalize below the height of 610's tank. In recent years, I'm not sure they were taking the A-tank along.

Wow. That explains that. Thanks.

At MRM. we have a 3 compartment tank car we are making into a combo water-oil Aux car.

Dave Huffman