Tender Derailments.

If these occur on straights it is usually due to a variation of moving weights (water sloshing page 35 from side to side, due to the baffle plates inside not keeping a dead balance of water), or to track irregularities. In such circumstances an oscillation is set up as explained in the previous paragraph. Tenders equipped with side bearings, having small clearances on both bogies, are liable to be derailed when they pass over a track with a low place in one rail. This is true even on tangents, as the surge of the water in the tank will probably cause the flanges of the front bogie to ride the rail at the low places.