As the many varied custom slip ring projects flow through the doors of United Equipment Accessories, occasionally one will seem to have a life and story of its own. Such was the case with the project involving the restoration and upgrade of the “Government Bridge” between Davenport, Iowa and the Rock Island Arsenal in Rock Island, Illinois. This particular bridge sits atop the lock and dam #15, right between the gates. It is what is commonly called a “swing bridge”. The bridge swings a full 360 degrees, allowing large boats and the tugs that push the numerous barges that travel up and down the Mississippi river channel to pass through. The bridge structure carries auto and truck traffic on its lower level and two railroad lines on its upper level. The mechanism that allows this rotation is situated on the center pier between the locks, supporting the complete 366 ft section of the bridge on a series of rollers. Around the base of this structure a pair of very large roller chain “tracks” crawl their way around what looks like a giant sprocket which is part of the main base of the bridge. These tracks are driven through shafts, one on each side of the bridge, that extend up to the control house over 50 feet above. Inside the control house is a large electric motor and a series of gears to drive these shafts.
This is the forth of a series of bridges at this location, which was the first railroad crossing the Mississippi river. The first bridge was built in 1856. It was burned two weeks after opening by the disgruntled river boat operators as they claimed it impeded navigation. It is speculated that the competition that the railroad was going to present was a big part of the issue. Abraham Lincoln defended the railroad in the court case that followed in 1857. A second bridge was destroyed by a tornado in 1868. To see a more detailed history click here. Or go to http://www.riveraction.org/node/28.
The present bridge was completed in 1896. Since that time, all the power for the motor as well as all controls and functions of the bridge was supplied by a wooden insulated slip ring that sat above the control house just below the high voltage lines that pass over the top of the entire bridge structure from shore to shore. These power lines are supported on their own set of rollers that allow the bridge to rotate below them while still supporting them. It was this space between these power line supports and the control house below that United Equipment Accessories was requested to create a custom slip ring to conduct the power and signals necessary for the day to day operation of this marvelous piece of engineering. Due to the exterior nature of this location an enclosure for the slip ring would have to be completely weather proof for all of the extremes that this part of the country can deliver, from -30F to well over +120F when baked by the summer sun. Since United Equipment Accessories wanted to provide a solution that would last as long as the predecessor slip ring, with a minimum of maintenance, a stainless steel enclosure and supports was clearly called for. A special rope type seal was used on the 6″ diameter main shaft coming in from above, as it would not be feasible to remove the enclosure or shaft for seal replacement. This type of seal can be wound around the shaft for replacement when required. It uses an adjustable gland to apply pressure, similar to the packing in a faucet stem. Because of the number of circuits and the size of the cables a 6-8″ bore range slip ring was required. This slip ring would be inverted in the enclosure, with the shaft coming in from the top and the core hanging down from it. All circuits coming into the slip ring from the power lines above would pass through the inside of the shaft to the rings. From there the brushes take the power from the slip ring and pass it to the cables that exit the bottom of the enclosure to the control house below. Included in the slip ring with the power circuits are several communication circuits for all purposes from the railroad signals to telephones and video monitoring equipment which was added to the bridge during this major upgrade. As part of the yearly winter shutdown the bridge goes through a full maintenance routine prior to reopening for the spring thaw. United Equipment Accessories, as part of its dedication to customers, has agreed to provide an annual inspection during this shutdown to insure that this slip ring continues to provide the critical power and control needed to support the bustling river transportation industry.
Above: Arial view of the bridge in operation as a boat steams into the lock.
Below: UEA Slip ring inside bridge