A few weeks ago, a beam in the Maasbracht lock that was intended for ships to approach had a big crack. A ship hit the beam with too much force. Installed as protection in the Dutch lock, the overall construction can nevertheless claim to have survived the accident well. As a precautionary measure for the lock door behind the bumper bar, special safety shock absorbers from ACE shock absorbers were used to protect the system from the worse.

The experts from ACE in the Netherlands, Ralf Küppers and Han Titulaer, were both proud and relieved when they learned of the emergency in the Maasbracht lock. "Relieved, because no one on the ship or on land has been harmed by the collision of the bumper beam. We are proud because our safety dampers have prevented the accident with the lock gate, "says Küppers, who is responsible for the sales of the Rhenish company in the Benelux countries.

His Dutch colleague Titulaer states: "Our client, the Dutch construction and steel company Mourik Limburg BV, and we are glad that our safety measures were planned well in advance and that the entire construction survived the accident very well." It should be noted that this extreme case had not occurred in the seven years since the plant was first put into operation.

In the project planning phase of the lock system, the partners involved had taken into account the impact of ships in the lock with the impact bar. Because when navigating a cargo ship in a lock, it is in principle conceivable that contact occurs, in this case between the lock door and the ship, as when parking an automobile in tight parking spaces.

Ballpoint pen principle makes the gas spring lockable on both sides

With loaded ships weighing up to 4000 t there is hardly a lock or hinge that would be able to stop the forces resulting from a maximum approach speed of 0,5 m / s in order to prevent the lock door from bursting. An uncontrolled and therefore very dangerous filling or emptying of the entire lock system with water would be the result. With a height difference of 12 m to be overcome, as is the case on site in Maasbracht, a real horror scenario. So it came about that the engineers made a virtue out of necessity and enabled controlled accidents via a bumper.

Customized bumper damper

In practice, this means that the captains of the cargo ships use and start the launch bars as a protective marker. Thus, the parking space, ie the lock, be chosen small. However, this is not the only advantage: in the case of the large differences in height in front of and behind the lock, it is possible to simply drive under the launch bar when the lock doors are open downstream - ie low water. The shock absorbers from ACE secure locks and beams here.

In the interpretation of the damper in addition to the already mentioned key data also an occurring Wasserschlag had to be considered. This refers to a physical phenomenon in which a strong mechanical shock is caused by water. At the end of the consultation and design by ACE, the safety dampers required energy to be degraded by 500 kNm, which requires a model of truly unusual proportions. The length of the damper specially designed for the lock is 2649 mm, its outer diameter 200 mm and its own weight 320 kg per model.

Calculate, design and order gas cable and gas pressure springs

The special design has an optimized characteristic curve, a fixed stop and a stroke of 800 mm and works according to this principle: The piston rod is inserted during the braking process and that hydraulic oil in front of the piston displaces simultaneously through all throttle openings. Due to the proportional to the stroke moved decreasing number of effective throttle bores not only reduces the retraction speed constant, it also remain the same before the piston resulting back pressure and the opposing force.

While the braking process of ACE miniature shock absorbers takes place so quickly that designers working with them for the first time have doubts about their effectiveness, the special airlock dampers need 3,5 s to cover the stroke of almost 1 m. So that you can return to the starting position after moving off, the safety dampers work similarly to the gas springs of ACE with nitrogen.

Collected in a gas reservoir, the oil displaced by the piston rod is compensated and pushes the piston rod back into its starting position when it extends. The XXXL dampers described here, like the heavy safety shock absorbers from ACE, are equipped with a separating piston nitrogen reset system to separate the hydraulic system from the gas storage tank.

Trigger bar is replaced, sluice damper not

In order to put the lock back into operation as quickly as possible, a new bump bar is needed. The ACE safety damper must be temporarily dismantled so that it can be replaced.

In order to speed up the process, the project office that is replacing the beam received all the necessary information electronically from Han Titulaer, such as the nitrogen being released from the interior, the dampers then being removed and reinstalled after the system has been repaired. This procedure is necessary because in the normally provided extended delivery state, removal and installation is not possible for reasons of space. At the end of all work, ACE takes over the inspection of the dampers, to which Han Titulaer comments: "Mourik Limburg BV and we are confident that the construction will survive the next seven years at least as well as the first."

Picture above: Launch bar at the lock in Maasbracht (NL) after collision with a cargo ship