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A bank engine (United Kingdom/Australia) (colloquially a banker) or helper engine or pusher engine (North America) is a railway locomotive that temporarily assists a train that requires additional power or traction to climb a gradient (or ''bank''). Helpers/bankers are most commonly found in mountain divisions (called "helper districts" in the U.S.), where the ruling grade may demand the use of substantially greater motive power than that required for other grades within the division. ==Historic practice== Helpers/bankers were most widely used during the age of steam, especially in the American West, where significant grades are common and trains are long. The development of advanced braking systems and diesel-electric or electric locomotives has eliminated the everyday need for bankers/helpers in all but a few locations. With the advent of dynamic brakes on electric or diesel-electric locomotives, helpers/bankers can also be used to provide more braking force on long downhill gradients. Bankers or helpers were historically positioned at the rear of the train, in which case they also protected against wagons or coaches breaking away from the train and running back downhill. Also, in a pusher role, it was possible for the helper/banker to easily separate once the train had crested the grade. Once separated, the banker would return to a siding or stub so as to clear the mainline and get ready for the next train. A common practice with knuckle couplers was to remove the knuckle from the front coupler. The locomotive would be brought up behind the last car of the train while the train was moving slowly. The air brake hose would not be coupled. When the train no longer required assistance, the helper/pusher would slow, then reverse and coast back down the grade to its siding at the bottom of the grade. This practice was outlawed in North America after the end of the steam era. Special heavily constructed cabooses were sometimes used in helper areas. Ordinary cabooses were built as lightly as practical and might be crushed by the helper/pusher's force, which could be as much as 90 tons. The heavy cabooses allowed crews to avoid the time-consuming procedure of splitting the train just ahead of the caboose.〔Source: photo of reinforced outside braced caboose: Richard E. Prince, NC&StL History & Steam Locomotives, p. 73.〕 Pushers/helpers were commonly designed to provide extreme power for very short runs; as a result they could not push at full power for very far before steam pressure dropped. But if it could push enough to get the train to the top of the grade, then it could build up pressure while coasting back down and while waiting for the next train to come along. This practice was common in Europe. Since it was not possible to remotely control a steam locomotive, each helper had to have a full crew on board. Careful coordination was required between engine crews to assure that all locomotives were operated in a consistent manner. Standard whistle signals were employed to tell the helper crew when to apply power, drift or brake. A misunderstanding of signals by a pusher locomotive crew could result in a major wreck if the lead locomotive applied brakes while the bank engine was still applying power. The usual result was that the train would experience a violent run-in (an abrupt bunching of train slack), resulting in the derailment of part or all of the train. The town of Helper, Utah was named after these engines, as it was where helper engines were kept to assist on the climb to Soldier Summit. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Bank engine」の詳細全文を読む スポンサード リンク
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