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Ed King's Air Brake Article, April 04 Trains

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A rather egregious mistake slipped into Ed's article in the April 04 issue on air brakes -- our mistake, not his. The incorrect information is that leakage in a brake pipe leads to a brake release. That's so obviously wrong I can't believe I didn't see it. The correct information is this: "Leakage, if allowed to be more than the allowable limit (5 lb/min) can greatly increase the time required to charge a train; with long trains it can take a lot longer to charge. Then, after you make a brake application, leakage affects the time required to get a train to release (some of the air you want to get back to the rear to make the brakes release has been lost to the atmosphere). With the AB valves as we covered in the story, they're designed to put some of the air from the emergency reservoirs into the brake pipe to assist in releasing brakes farther back in the train, but that air must also be replaced. Leakage makes that a more difficult task. Without engine brake valves with pressure maintaining, when the brake valve handle is placed in lap after making an application, leakage will cause the application to increase; remember, in lap, no air is being put into the train line. If this happens, the brakes will eventually apply hard enough to cause a stop. Two things mitigate this condition - the pressure maintaining feature, which will hold the brake pipe pressure at the level of the application against reasonable leakage (most were effective for more than the legal leakage), and retainers. Retainers held the brakes on a train while the first application was made and then released so the brake pipe could be recharged. An example in practice: I was running a long train one very cold night with a locomotive in the lead without pressure maintaining. All that was necessary was to lap the brake valve; leakage would make a brake application for me." -- Ed King
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