Hydraulics experts help to upgrade historic harbour equipment

Created in the early 19th century when lock gates were installed on a tidal stretch of the river Avon, Bristol's floating harbour is a premier tourist locations, attracting thousands of visitors over a 70-acre site. The floating harbour is so called because the water level always remains constant and is not adversely affected by the tide on the river.

Though no longer the focus for commercial shipping activity in the city, the system of bridges and locks that makes up the harbour still enjoys significant leisure boating traffic and incorporates comprehensive vehicle and pedestrian access to its many attractions that span a large area of the city centre.

In the Hotwells area of the city, the floating harbour rejoins the tidal river Avon via a series of locks and the wide Cumberland Basin. Among several pieces of major infrastructure in this area is Junction Lock Bridge, a 650-tonne swing bridge with two vehicle carriageways and pedestrian walkways. Built in 1925, the structure was becoming increasingly unreliable and costly to maintain. Bristol City Docks therefore decided to include it within the scope of its operational infrastructure project to upgrade large sections of the harbour.

Operating system upgrade

Bosch Rexroth has significant experience in the civil infrastructure sector and was chosen to undertake a comprehensive 640,000 refurbishment of the bridge's operating system to include the installation of power units and new control stations, and replacement of cylinders and hydraulics.

Given the size and weight of the bridge, the two central focuses of the project related to its drive system and the centre lift. Initially, Bosch Rexroth set about replacing the antiquated chain-drive system with a much more robust and more easily controlled cylinder-based drive mechanism that could operate with much greater power and precision.

This was then complemented by the installation of a new, double-acting centre lift. With an 800mm bore, 100mm stroke and lifting capability to raise the entire bridge deck, its cylinder-based mechanism has proven significantly more powerful than its Victorian counterpart and is much better equipped to deal with the potentially damaging effects of regular traffic vibration and side loads caused by wind.

Previously, control of the bridge's water hydraulics system was undertaken by cumbersome operating levers that were prone to maintenance problems and vandalism. As part of the overhaul, this was replaced by a state-of-the-art hydraulic system, complete with electronically operated local control stations, and new hydraulic power units (HPUs) to control two of the bridge's associated mitre gates and four of its sluices.

Two new plant rooms were also built on each of the bridge's north and south quays to house the control units and HPUs. These were constructed at a raised level to reduce the risk of flooding, which had previously been problematic. Electronic control screens within both plant rooms were also installed to give site engineers up-to-the-minute data on the performance of the bridge, gates and sluices.

Gate upgrades

Also within the scope of the project was the upgrading of the operating systems of two 8m deep mitre gates that are linked to the bridge and ensure the floating harbour remains full. A special shear mechanism was installed to protect the cylinders that operate these gates.

Furthermore, the Bosch Rexroth team also changed the hydraulic cylinders operating the site's system of sluices to ensure greater reliability and ease of operation.

Commenting on the project, Steve Smith, UK industry sector manager at Bosch Rexroth, said: "While the bridge had given many faithful years of service, it was clear that its Victorian infrastructure was struggling to cope with the rigours of the modern day. It has therefore been really satisfying to deliver a far more reliable, easy to operate and maintain and, ultimately, better performing solution, which will serve the needs of land- and water-based traffic alike for many decades to come."

Follow the link for more information about industrial hydraulics from Bosch Rexroth.