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Langton Dock for caisson refurbish

As part of the upgrade of a busy European port, the lock's caissons had to be refurbished. 

As part of the upgrade of a busy European port, the lock's caissons had to be refurbished. Pumps were required, which would empty the caissons within a three hour window of opportunity. The supplied pumps achieved this without the expense of having to take the lock out of service.

High Volume Pumping

Faced with the requirement to pump three million litres of water from Liverpool's Langton Dock in just three hours – with potentially serious and costly consequences if things went wrong – Exsel Pumps decided to rely on variable speed drive systems from Ralspeed and generators from PE Generators (part of the Turner Group) to control the pumps it would use for this challenging project.

Currently, £10 million is being invested in upgrading lock gate facilities at the Port of Liverpool, one of the largest and busiest container ports in Europe. An important part of this project involves refurbishing the caissons (sliding watertight doors) used in Langton Lock. This Lock, one of the busiest in the port, is divided into three sections, with caissons between the first and second sections, and between the second and third sections.

It would be too costly and disruptive to take the lock out of service for the whole duration of the project, which will take around three years. The decision was therefore taken to refurbish the caissons one at a time, which would allow the lock to continue to function while the work was being carried out, albeit with reduced flexibility.

The first phase of the project was the removal of the 1,600 tonne outer caisson, which was then sailed to the top end of the dock and moored up. Once this was complete, the next phase involved removing the 4,000 tonne refurbished middle caisson from the recess from where it had been refurbished. The caisson was sailed down the lock to the outer recess, where it was then reinstalled and commissioned. The next stage was to sail the outer caisson into the refurbishment recess for repair and refurbishment.

Pumping Solution

To achieve this changeover of the caissons it was necessary to pump out and refill the caissons recess, which holds three million litres of water, several times. And, in order to limit the amount of time for which the lock was out of service, and to cater for variations in the tides around the dock, the time available for each of the emptying and filling operations was to be completed in less than three hours.

Exsel Pumps has wide knowledge and experience of supplying pumping systems, for such demanding applications, and offered four 200 kW pumps, two of which were configured for emptying the dock, the other two for filling it. The engineers at Exsel knew, however, that they would need dependable variable speed drives to control these pumps not only to ensure smooth flow of water, but also to minimise the peak load on the electrical supply when the pumps started. As the electricity supply was generator fed, the use of a variable speed drive enabled a reduction in generator size and a reduction in fuel consumption.

Since the drives would be used outdoors, they needed to be weatherproof and, because of their proximity to the dock, they also needed to be capable of resisting the effects of almost continuous exposure to seawater and salt spray. Further, since the caisson exchange was taking place in the middle of winter, the drives had to able to operate reliably at low temperatures.

For this project, Ralspeed supplied two custom-built drive systems, each comprising a 200 kW Vacon NX drive and ancillary components mounted in a rugged weatherproof enclosure. Since filling and emptying operations would never be carried out simultaneously, rather than providing four separate drives Ralspeed supplied a changeover switching system which would allow the drives to be switched almost instantly to work with either the filling or the emptying pumps. This arrangement provided a very cost-effective solution.


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