Sanding the flues. Black Hills Central Railroad Locomotive #108 pours out a strong, salt and pepper plume as she hauls the first "1880 Train" of the day past the second crossing at Old Hill City Road (MP .5), just outside Hill City, SD. This is about the most smoke you'll ever see from this locomotive as normally, she runs clean-stack nearly all of the time. On this particular morning, the air was cool, yielding a steamy, white plume as the train approached the grade crossing and just as they entered the roadway, the crew began to sand the flues. On oil-burning locomotives such as the 108, this procedure involves introducing sand to the firebox when the locomotive is producing a strong draft, such as on a steep grade like you see here. That sand is pulled through the boiler flues by the draft, and effectively sands off any soot products which have built up on the inside of the tubes. Cleaning the flues in this manner, improves heat transfer and engine efficiency. It also makes for a very dark exhaust plume for at least a few seconds. Although the passengers in the open cars will likely get "dusted" with sand grains, my experience on this train is that it doesn't soil clothing. As this is happening, the narrator on the train typically warns the passengers to expect a little dusting.
