A hub is a device for horizontal rotation of rail vehicles, rare road vehicles. This operation was carried out primarily for steam locomotives with tender, which can only drive in the forward direction with their maximum speed. In addition, turntables are used for space-saving converting a vehicle in adjacent tracks, for example, to accommodate them in the engine shed. A rotating part in a bridge shape is sometimes also called revolving stage.
The hubs evolved from simple systems, which were arranged in early railway stations in the track area to turn locomotives in the opposite direction. They were covered to protect people from falling into the pit and therefore looked like slices from. The turntable is a machine- technical system with which a vehicle ( mostly rail vehicle ) can be reversed, or with between 2 or more tracks, optionally, a driveway can be made. Often, the hub of connection radial tracks in a small space serves. By the rotation of the turntable bridge locomotives or other vehicle into the desired position can be made. A distinction Cross hubs (for simple conditions, eg in mining and railways ), segment hubs ( in confined spaces, such as railway sidings ) and bridge turntables with and without towing frame. Always there are steel constructions where bridges carry the rails to accommodate the vehicles. The turntable pits are circular or circle segment, and may have different diameters. The size of the hubs developed with the length of the locomotives. In Prussia, 8 to 12 m were sufficient, 1889 14 m were required in 1892 16 m. Unit hubs of the Reichsbahn in Germany in 1920 had 20 m, since 1928, has a diameter of 23 m or 26 m later, in Switzerland 13 m or 16 m. Other dimensions are possible. The bearing of the turntable bridge in the middle or at the pivot point is at the King chair. The bearing of the turntable bridge at the ends is done with - usually - flangeless loose wheels that roll on the laid in the turntable pit turntable roller ring. For larger hubs are often found several hub running treads. Must be between the turntable and the subsequent fixed track bridge a secure connection can be made by means of locking means. This locking device is often coupled with shunting signals and the turntable control. Turntables were and are rotated by muscular power, in the 20th century, the drive came from electric motors, in rare cases, diesel engines and compressed air. For motor-driven turntables usually 2 of the 4 wheels are driven.
Since most steam locomotives are allowed to drive with a Tender in forward direction at full speed, it is necessary to turn such a locomotive when the journey in the opposite direction to be recorded. Turntables were therefore primarily at terminal stations, for example, the first station of Altona station in Hamburg or Berlin. In Bahnbetriebswerke they were directly in front of the roundhouse, which were designed in large depots as roundhouse. There she also gave access to the individual stands that would otherwise have been possible only with an elaborate course road. Occurred mainly in the 1950s, the large decline of steam locomotives and therefore time delay that the hubs.
Today at railway depots mainly sliding platforms to be installed, since they make it possible with the least amount of space required to operate several parallel tracks. One needs only a parallel approach track and then storage space on both sides of the stage use ( Neustrelitz, Dresden Altstadt ).
Many locomotives European railway administrations are usually bi-directional vehicles for which a hub is not necessary. Thus, hubs are in regular railway operations become rare, but still often seen in railway museums. A bawanced practical reasons new construction, as in 1988 at the Vitznau- Rigi -Bahn, is a rarity. Rather, it happens that, as in the Minehead Railway Station a 1968 remote revolving stage, consisting primarily of nostalgic reasons, it is built in 2008. Unlike in North America, Australia and New Zealand, where many locomotives on one side only have a cab, especially large, diesel-electric powered. Thus, there are even more hubs in constant use and even sometimes newly built ( for example, the Canadian Pacific Railway in East Binghamton (New York) shortly before 2000).
Large hubs were about 1941 by the Union Pacific Railroad for their Class 4000 steam locomotives, called " Big Boy " (total length: 132 ft 9 ¼ in ( 40.47 m) Wheelbase: 117 ft 7 in ( 35.83 m ) ) built 135 -foot turntable (41 m) in Ogden (Utah ), Green River (Wyoming) and Laramie (Wyoming). At least in the north ( California ) existed until a fire in 1962, a 150 -foot turntable ( 45.72 m ). Another way to turn locomotives, track are triangles. With the appropriate cable lengths and entire trains can thus be reversed. Extra one track triangle was built for even longer steam locomotive PRR Class S1. In comparison, had the largest diesel-electric locomotive, the EMD DDA40X, a length of almost 30 m, and it is in these types often run as multiple units, which was not common for steam locomotives.
Another application of turntables is the turning of snow plowing. Therefore, in snowy regions remained the hubs of the era of steam locomotives also obtained.
Particular uses of A curiosity was the hub of Corkscrew Gulch Silverton Railroad in Colorado (USA). Since the track led into a canyon, there were steep gradients and small radii. Since the slope at Corkscrew Gulch for a turning bow was too steep and should continue the route in the opposite direction, where a hairpin was constructed in which the train had to change the direction of travel, and to go to the respective main track. There, a turntable was installed, which was accessible from both the mountain and the valley side of a slope. Upon passing the cars were separated from the locomotive and turned the locomotive. After the locomotive had cleared the track, the rest of the train on the tilt was performed on the turntable. Provided that the total length of the wagon length exceeding the stage of the rotary disc, this had to be individually supplied to the turntable. The extreme slope of the line anyway allowed only very short trains. Then the locomotive sat back, and the wagons were hitched again to proceed.
In the Vienna metro, it depends on the U2 line by passing over several stations circle part to one-sided wear. To counteract this, it turns the respective sets at certain time intervals. Since half a two-car is not drivable, has started operations in November 1988 turntable when operating station aqueduct meadow (48 ° 14 ' 29 " N, 16 ° 21' 47" O48.24146111111116.363180555556 ) has a diameter of 40 m, making it the largest in Europe.
The ship lift at the Krasnoyarsk reservoir can be described structurally as a cog railway. Since, in contrast to channels with continuous constant water drainage in the reservoir and the lower river are high fluctuations, no sealed with gates blunt end can be used. The inclined rail portion shall come up with a horizontally oriented trough it into the water, taking the ship and lifts it up the hill to the dam crest. The vehicle then turns on an approximately 105 -meter hub by 140 ° and can then descend into the upper basin again with horizontal trough.
Rarely hubs are also used in road-based vehicles, a well-known example is the hub of the lower castle, a hub for trolleybuses in Solingen district Burg on the Wupper. Two additional trolleybus turntable formerly existed in Great Britain, these were the hub and the hub of Christchurch Longwood. A fourth trolleybus turntable existed from 1976 to 1985 in the trolleybus tunnel of Guadalajara in Mexico. The limited space in the underground let there be no other solution.
Otherwise, small hubs for passenger cars in the private sector are used in confined spaces, particularly at conversions of older apartment buildings, where could not be taken from the outset to meet the requirements of consideration.
A special type is the segment turntable. For her, the bridge girder sweeps only a segment of the circle. It can therefore not fully rotate, so it is only suitable for turning of a vehicle, if it can be rotated at least 180 degrees. Such a segment hub is located, for example, in front of the roundhouse in New Market Wirsberg.
It is primarily used for space-saving implementation of vehicles on subsequent tracks, sometimes in a smaller footprint than turnouts. However, the elaborate construction and maintenance also had this type rarely reach for execution. A recently newly built hub segment is to be found in Bezau station of Bregenzerwaldbahn. Further, no longer operated segment hubs are located at the main station in Bayreuth, in Bebra railway station or in the Klutz station at the end of the railway line Grevesmühlen - Klutz.
There are also rotary discs which can be moved back and forth between two points of rotation, and are better suited for distributing locomotives in different tracks.
Another special design is the double turntable. It was installed at places where a lot of locomotives should be turned off to save space.
In this design, the radius of action of two turntables are carried out overlapping. Thus, the two pits are connected to each other and intersect the hub rolling strips in the outer pit area, due to the overlap.
Double turntables possessed example, the depots of the Altona train station and in the operating station Cologne.