Rotary snowplow

A rotary snowplow is a piece of railroad snowfighting equipment. It is characterized by the large circular set of blades on its front end that rotate as a unit to cut through the snow on the track ahead of it. In this way, a rotary snowplow is similar to a tunnel boring machine that was first used to drill the Hoosac Tunnel in 1853.

The rotary was invented by a Canadian dentist in 1869, but a prototype wasn't built until the Leslie Brothers constructed one in 1883.

Operation

Wedge snowplows were the traditional automated method of clearing snow from railroad tracks. These pushed snow off the tracks, deflecting it to the side. Deeper drifts, however, cannot be easily cleared by this method; there is simply too much snow to be moved. For this purpose, the rotary snowplow was devised.

When a snowfall or snow drift becomes too deep, railroads call on their "big guns" in snowfighting equipment - the rotary. The plow is not self-propelled, so one or more locomotives are coupled behind it to push the plow along the line. An engine within the plow's carbody rotates the large circular assembly at the front of the plow. The blades on this wheel cut through the snow and force it through a channel just behind the disk to an output chute located at the top of the blade assembly.

The chute can be adjusted to throw the snow to either the left or the right side of the tracks. An operator sits in a cab just above and behind the blade assembly to control the speed of the blades and the direction of output for the snow from the output chute. With the advent of dieselization, MU controls have been added to the cabs, so that the pushing locomotives can also be controlled from the plow's cab.

In areas of particularly deep snowfall, such as California's Donner Pass, railroads sometimes would create a train consisting of a rotary snowplow at each end (with the blade ends pointing away from each other), and two or three locomotives coupled between them. With a plow on each end, the train would be able to get itself back to its starting location even if the snowfall was heavy enough to obscure the tracks it had just passed over. Such a train would also be able to efficiently clear multiple track mainlines as it could make a pass in one direction on one track and then reverse direction and clear the next track. This practice became standard for the Southern Pacific Railroad on Donner Pass following the January 1952 stranding of the "City of San Francisco"; during attempts to clear the avalanches that had trapped the train, two rotary plows were themselves trapped by further avalanches, and the crew of a third was killed when their plow was directly hit by an avalanche.

Rotary snowplows are highly expensive due to their high maintenance costs, which the owning railroad must pay regardless of whether they are needed in a given year. As a result, most railroads have eliminated their rotaries, preferring to use a variety of types of fixed-blade plows that have significantly lower maintenance costs, in conjunction with bulldozers, which can be used year-round on maintenance-of-way projects. In addition, because rotaries leave a cut in the snowbank that fixed-blade plows cannot push snow past, once rotaries have been used, they must be used for all further significant snowfalls until the snowbank has melted. Since rotaries, which need some form of fuel to power the blades, also cost more to operate than fixed-blade plows, they are now generally considered to be a "weapon of last resort" for the railroads that own them; they are only used when snow is too deep or heavy for fixed-blade plows.

The few remaining rotary plows are either owned by museum railroads, or are kept in reserve for areas with poor road access and routine severe snowfall conditions; the largest remaining fleet of rotaries consists of Union Pacific Railroad's six ex-Southern Pacific plows reserved for Donner Pass.

Power

Early rotaries had steam engines inside their carbodies to power the blades; a few are still in working order, and in particular one on the White Pass & Yukon Route in Alaska performs annual demonstration runs through thick snow for the benefit of photographers and enthusiasts. Newer constructed rotaries are either diesel or electric powered; in the latter case, an electric supply is required. Many steam plows were converted. Some electric plows can take their power from a locomotive, while others are semi-permanently coupled to power units, generally old locomotives with their traction motors removed; these are colloquially called "snails". (This is derived from the fact that engineless but motored units that take their power from another locomotive are "slugs" - thus the opposite, with engine but no motors, is a "snail").

Northern Pacific Rotary 10 steam snowplow

The Northern Pacific Rotary 10 steam snowplow built in November, 1907 is currently owned by the Northwest Railway Museum and is on display in Snoqualmie, Washington.

Preservation

Southern Pacific rotary snowplow MW208 is preserved in operational condition at the Western Pacific Railroad Museum at Portola, California. This rotary was involved in the 1952 City of San Francisco rescue.

Another one is on display at the Lake Superior Railroad Museum in Duluth, Minnesota.

ee also

*Snow blower

External links

* [http://www.collectionscanada.ca/trains/kids/h32-5090-e.html The Rotary Snowplow - a Canadian Invention] - quick overview with some historical photos.
* [http://membrane.com/~elmer/rail/units/rotaries.html Rotary snowplow list] - lists rotary plows in existence, some of which are still in use today.
* [http://n6ecv.net/Rotarys.html SP Rotary Snowplows] - Many photos and details of rotaries that operate over Donner Pass in California.
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