Some information passed on to me by Jerry Day. He wrote an article on D&RGW flangers for the Prospector magazine in 2012.
March 7, 1891
A Trip with the Flanger
One day last week a reporter for the Tribune boarded engine Number 251 which was making a trip to Crested Butte with the Denver and Rio Grande flanger. An engine, flanger, and caboose are run ahead of each train that goes to Crested Butte in order to keep the ice and hardened snow away from the rails, thus making it possible for one engine to pull a large train of cars.
We left Gunnison at 9:30 o'clock in the morning and arrived at our destination about 11:00 o'clock. Just after getting outside the city, the engineer opened his air brake valve, called the three-way cock, and the great plows began to lower. Soon they were plowing through the hardened snow. The flanger is a small car which weights probably from four to six tons. One large plow or shoe runs on each rail. On the outside the snow is taken off even with the rail, but on the inside the plow cuts a depth of nearly two inches. The plows are operated by air from the engine. When the air is used on the flanger, the setting of the brakes on cars has to be done altogether by hand. As a switch or wagon road is reached, the engineer releases his air and the knives are raised until these are passed.