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[traingang]

Okay, I'm ashamed to say my 9-year old son noticed this before I did.  Here in Lima, Ohio, we have tank cars coming and going from the refinery (Valero) and the soap factory (P&G).  My son observed that many tank cars are bowed in the middle; that is, the ends of the tank car are higher than the middle.  When asked why, I speculated that when filling the car, this may allow room for splashing/sloshing, figuring that the force of the liquids going in would eventually push a significant volume of other liquids to the sides and slightly up the sides, which could be better accommodated with the bowed shape of the tank car.  No pun intended, but am I on "the right track" with this response to my son?

mgb/lima,o  _ _ . _

[ezielinski]

I always thought it was to facilitate complete emptying of the cars contents.

[ndbprr]

It is to allow gravity to empty the cars completely.  You should also note that tank cars today use the tank as a structural part of the car and do not have in underframe as they did years ago.  The saddle that the truck attachs to is welded to the tank directly.  Federal safety rules after a number of catostrophic wrecks mandated some other rules also.  you may note some cars have big plate shields on the end to prevent another cars coupler from puncturing the tank.  In addition many have a much larger coupler in height designed to prevent the two cars from separating in an accident.  There is also a rule about placing flammable materials within a certain distance of the engines to protect crews.

[Anonymous]

The bows also guarantee a volume of air above the load for expansion.  Some liquids expand in the sun, and overflows are not nice.

Mark in Utah