Thursday, February 26, 2009

Spacing out the ties

Railroad ties are ubiquitous and often taken for granted yet there is more to a tie than meets the eye. At the Northwest Railway Museum, a standard cross tie is 6 inches by 8 inches by 8 feet long and it is treated with either creosote or copper naphthanate. In well-drained ballast (the crushed rock the tie is placed in), it will last for 30 or more years. and over that time support millions of tons of trains.

Ties support the rails and distribute the weight of a passing train on the ballast. Ties also hold the track "in gauge," which is the distance between the two rails. For maximum effectiveness, ties must be evenly spaced. But when trains are braking or accelerating, or even just as the rails expand and contract in the heat and cold, there is a tendency for the track to "creep" and this causes ties to "creep" too. The end result is crooked alignment and uneven spacing. Once upon a time, badly misaligned ties were straightened by digging out the ballast from around the tie and moving it with a long steel bar -all by hand.

In the 1970s, some enterprising design engineers devised a hydraulic tie spacer. A diesel engine drives a hydraulic pump to pressurize a fluid - usually oil - to about 2,000 pounds per square inch. This pressurized fluid is used to force giant pistons back and forth. Those pistons are connected to a steel foot that can hook the end of a tie and move it in either direction. Of course the hydraulics are used to perform other functions too including propulsion.

The Northwest Railway Museum has a tie spacer that came from the British Columbia Railway but is similar to units once used in Washington by the BNSF and Union Pacific. Last fall, the tie spacer was rehabilitated in the Conservation and Restoration Center and is now used to help maintain the railway.

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