Electro-hydraulic drives for the tandem locks at Münster

Electro-hydraulic drives for the tandem locks at Münster
Marginal Column

July 2015


The tandem locks are an important gateway for European shipping and, owing to the design with two parallel chambers, they conserve both water and energy.

The Dortmund-Ems Canal is one of the most heavily travelled waterways in Germany. It links not only the Rhine, Weser and Elbe rivers, but is also an important section of the east-west waterways reaching into the Central Europe. In the southern section, near the city of Münster, locks compensate for a height differential of 6.20 meters. When the canal was built in 1899 there was only a single lock; as of 1913 and 1926 the number of locks totaled three. This solution provided excellent service for a long time. But recent decades have witnessed major changes in inland shipping. While tugboats made their mark on shipping in the past, today’s large motor ships and barge trains, up to 189 meters in length, are standard.

Environmentally friendly new structure

That is why Germany’s Water and Shipping Administration decided to build new tandem locks with two identical chambers and useable dimensions of 190 meters in length, 12.5 meters in width. This important project in the upgrading program for the southern stretch of the Dortmund-Ems Canal ensures that significantly more than the previous 16,000 ships and barge trains can now be handled.

To avoid interrupting shipping during the construction work, commenced in 1991, the effort was carried out in stages. The first lock chamber went into service in 2009 and its sister chamber was completed in April of 2014. The loads on the ships passing through the twin locks annually correspond to the total capacities of more than 510,000 trucks. In this way the locks at Münster contribute to relieving the load on the roadway network and to reduce CO2 emissions in Germany. In addition, the two chambers transfer only 8,000 cubic meters of water during each ascent and descent cycle, thus reducing water consumption. This also saves energy, since less water has to be pumped upstream from the lower pound. All the movements required for using the locks are powered by electro-hydraulic drives built by Rexroth. They open and close the flap and the miter gates along with the eight bypass connections in the longitudinal culverts and two lateral culverts.

The design for the hydraulics makes it possible to separate the power conversion section from the drive cylinders. Thus the hydraulic power units can be placed in protected spaces below the locks. Only the cylinders directly at the gates and closures are exposed to splashed water. Each of the 16 hydraulic power units used here is made up of two redundant motor pump groups. The axial piston pumps, model A10VSO, built by Rexroth are especially quiet in operation and have efficiency of considerably more than 90 percent. In addition, the hydraulic fluid used in Münster is environmentally friendly, is quickly biodegradable, and achieves the same service life as mineral oil fluids.

Cylinders with a stroke of 2,200 millimeters open and close the miter gates, weighing 52 tons, applying up to 450 kilonewtons of force. All the cylinders are executed with corrosion protection for extended service lives. More than 30 years ago, Bosch Rexroth was the first manufacturer to apply ceramic coatings to piston rods used for civil engineering and offshore. Since that time the company has analyzed the operational data for the more than ten thousand large cylinders used in a wide variety of applications, in the most extreme settings, all around the world. An importing finding from this effort: reliable corrosion protection involves far more than coating the piston rod. It is an interplay of the coating, the tribology of the system, and a sealing technique appropriate to the application that ensures comprehensive, long-lasting protection.

Non-contacting path measurement

The CIMS (Cylinder-Integrated Measuring System) installed entirely within the cylinder measures the position of the piston rod – without the need for mechanical contact with the surface of the piston rod. In close cooperation with the automotive experts at Bosch, Bosch Rexroth developed a new generation of sensors for use in CIMS. They are especially robust and can withstand vibrations and shock. The system has no wearing parts or effects on the piston rod. Ridges beneath the coating on the piston rod cause changes in a magnetic field generated by the position measurement system. The CIMS sensor registers this variation and conducts a high-precision evaluation. The operating status of the integral path measurement system can be called up and evaluated by technicians using a PC or the PLC controls. Rexroth installed three CIMS sensors in each of the cylinders at the Münster locks. This ensures redundant position measurement. This was the very first use of this new CIMS generation. That is why Rexroth combined at each cylinder the new systems and the time-tested models from the previous series so that they could be compared one with another in real time and then optimized.

This is how the tandem locks work

 This is how the tandem locks work

Once one chamber is filled with water (upper pound level [1]) and the second is emptied (lower pound level [2]) the locking process can begin. The flap gates,13.2 meters wide, at the upper end [3] and the miter gates at the lower end [4] are closed.

Water flows from the chamber with the upper level, through a longitudinal culvert [5] on either side of the chamber and through two lateral culverts [6], into the chamber with the lower water level. Owing to this exchange, both chambers achieve identical levels midway between the two target levels. While the remaining water from the chamber for downstream travel is discharged into the lower pound, the other chamber is topped up via the inlet structure. A total of ten valves in the culverts regulate the water level.

Since the Dortmund-Ems Canal does not have any natural inflow, water is a precious commodity. Every liter discharged into the canal at the lower end has to be pumped back to the upper pound. And here the benefits of the tandem locks come fully to bear. During each locking procedure the two chambers exchange 8,000 cubic meters of water - half of the amount required per chamber. As a consequence, far less water is “lost”, which then has to be pumped back uphill. This lowers water consumption and thus also the amount of energy consumed by the pumps.