Thinking About Stopping

It is understood that the very idea of air brakes may cause eyelids to droop, but on 5 March 1872, George Westinghouse was awarded a patent for his triple-valve air brake system for railroads, inspired in part by Elisha Otis’ elevator brake that dated from the 1850s, Dull as dust, right?  Well…

By the mid 19th century, railroads the world over were expanding exponentially, and so were accidents.  Most trains used either a mechanical linkage to operate any brakes they had, or used a brake car at the back of the train to slow the vehicle, adding to the reversal pressure of the locomotive and its own steam brakes.  But as the trains got longer it got harder to stop them.  On long trips through desolate areas, the brakeman fell asleep or the signal device failed.  Simply put, stopping the train depended on more human input than the engineer needing to stop.

Westinghouse’s brakes were unique not because they were air actuated, but because they were spring actuated; they were (and are still) air released.  Almost every air brake today in trains, trucks, cranes (yes, cranes), construction equipment, even elevators (using a hybrid system) operate on the theory that the stopping system has to be operating for the vehicle to move.  The air system has to be pressurized, and the controls and drive train available to operate the vehicle.  But with Westinghouse brakes all that ended.  The engineer hit the brakes, releasing the pressure on all the brakes in the train and they stopped the vehicle.  More important, the brakes activated when the system failed, increasing safety.

While it was the Americans that invented the air-release brake, it was Europe that first exploited it more completely.  Answering the need for an air supply, a diesel engine was mounted in a car immediately behind the locomotive tender to drive a compressor to pressurize the main air tank in Britain.  Diesels burned oil rather than coal, sparing the need to shuttle coal into a furnace to maintain the system.  As the technology improved, oil-burning locomotives were built with compressors, and finally the diesel-electric trains emerged after WWII with stand-alone compressors.  Today’s diesel-electric locomotives are rated by how much they can stop, not how much they can pull.

And as safety improved so did the size of the trains.  Similarly, so did construction equipment, especially with the emergence of Clessie Cummins after WWI.  Trucks and other heavy vehicles developed other braking systems, including the engine (reverse compression) brake.  But Westinghouse (and Otis, in a different way) started engineers thinking about the consequences of getting large machinery moving, and better how to stop them.

Modern large vehicles, from the mine pit to the rail head to the grocery store to the road construction project all use one version or another of the Westinghouse brake.  And that’s worth stopping and thinking about.

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