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In rail terminology, a railway turntable or wheelhouse is a device for turning railroad rolling stock, usually locomotives, so that they can be moved back in the direction from which they came.〔 (【引用サイトリンク】title=Locomotive/Railway Turntables )〕 This is especially true in areas where economic considerations or a lack of sufficient space have served to weigh against the construction of a turnaround wye. In the case of steam locomotives, railroads needed a way to turn the locomotives around for return trips as their controls were often not configured for extended periods of running in reverse and in many locomotives the top speed was lower in reverse motion. In the case of diesel locomotives, though most can be operated in either direction, they are treated as having "front ends" and "rear ends" (often determined by reference to the location of the crew cab). When operated as a single unit, the railway company often prefers, or requires, that a diesel locomotive be run "front end" first. When operated as part of a multiple unit locomotive consist, the locomotives can be arranged so that the consist can be operated "front end first" no matter which direction the consist is pointed. Turntables were also used to turn observation cars so that their windowed lounge ends faced toward the rear of the train.〔The Elements of Railroad Engineering, 5th Edition, 1937, William G. Raymond. Published by John Wiley and Sons, New York〕 ==History== Early wagonways were industrial railways, transporting goods - initially bulky and heavy items, particularly mined stone, ores and coal - from one point to another, most often a dockside for loading onto a ship.〔 These early wagonway engineers initially used just a single point-to-point track, and when in operation were required to either position a truck in an alternate location or move it around other wagonway using equipment, would simply manoeuvre it by hand. Whilst the use of man or horse power limited total train weight, this lack of switching limited the total weight capacity of any loaded wagon combination. Resultantly, the first railway switches were in actual fact either wagon turnplates or sliding rails. Turnplates were initially made of two or four piece of wood which replicated the track running through them, and circular in form. They were the diameter of the wagons used on that wagonway, and swung around a central pivot. Loaded wagons could hence be moved onto the turnplate, and then by moving the turnplate through 90 degrees, allowed the loaded wagon to be moved onto another piece of wagonway. Thus, the limit on total loaded wagon movement hence raised to a combination of the strength of the wood used in the turnplates/sliding rails construction, and the support available to it. When iron and later steel replaced stone and wood as the rails, total capacity of a loaded wagon combination rose again. However, the problems with turnplates/sliding rails were twofold. Firstly, they were relatively small - often no more than a in length - and thus limited the total wagon length that could be turned. Secondly, their switching capacity could only be accessed when the wagon was both on top of them, but most critically still. With busier wagonways and heavier loads, this limited the total capacity of any wagonway. The railway switch which overcame both of these problems was patented by Charles Fox in 1832. As steam locomotives replaced horses as the preferred means of power, these became optimised to run forward in one direction, most often for operational ease of the driver/fireman and to provide some weather protection.〔 This necessity to turn heavy locomotives required an engineering upgrade to the existing turnplate technology. Hence like earlier turnplates, most turntables consisted of a circular pit in which the steel bridge rotated. The bridge was typically supported and balanced by the central pivot, ton reduce the toal load on the central pivot, and balanced to allow easy turning. This was most often achieved by a steel rail running around the floor of the pit that supported the ends of the bridge when, but only when a locomotive entered or exited the bridge. Turntables have a positive locking mechanism to prevent undesired rotation and to align the bridge rails with the exit track. Rotation of the bridge could be accomplished manually (either by brute force or with a windlass system) by an external power source, or by the braking system of the locomotive itself, though this required a locomotive to be on the table for it to be rotated. The turntable bridge (the part of the turntable that included the tracks and that swivelled to turn the equipment) could span from , depending on the railroad's needs. Larger turntables were installed in the locomotive maintenance facilities for longer locomotives, while short line and narrow gauge railroads typically used smaller turntables as their equipment was smaller. Turntables as small as in diameter have been installed in some industrial facilities where the equipment is small enough to be pushed one at a time by human or horse power. 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「Railway turntable」の詳細全文を読む スポンサード リンク
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