Hopper rail car dumps?

Question

For any railroaders out there: can anybody give me figures for the pressure drop inside a covered hopper railcar when the load is released?

I can do math on a fictional solid mass dropping out the bottom, which almost instantly increase the volume by some high percentage, thus decreasing pressure. But what about a granular or chunk substance (coal would be a good example)?

Answer 1

I don't have any math formulas for the vacuum created by emptying a load. With covered hoppers, there is a vent at the ends of each car to equalize the pressure of an exiting load. Small grains such as wheat, soy beans, and even granulated sugar can suck in and ruin the top hatches on a hopper if the vents are clogged. It's not real common, but it does happen. In one of the towns I travel through there is a grain elevator with large round silo type storage bins. One bin wasn't properly vented during unloading. The vacuum inside partially collapsed the structure. It looks like a giant smacked the side of the bin with a bat. That had to hurt someones budget.

Answer 2

Wow, interesting question, you would have to know the rate the product is being emptied at. different products and different designs of cars would change the equation considerably.

The reason the doors are left open is exactly BECAUSE the pressure can drop, like derali stated, it can do significant damage if the car is not properly vented, I have heard of the fiberglass door on top of covered grain hoppers sucked through the opening and ruined.

Answer 3

The pressure doesn't drop, because the fill doors on top are open.