At its simplest, the structure comprises a wheel rim, rotating hub and fixed spindles mounted on four support legs. The rim is 240m in diameter and assembled from eight segments that are welded together and connected to the hub by cable spokes, each longer than a full-size football pitch. For the wheel assembly, the height of the ‘Ain Dubai’ takes it well beyond the reach of a traditional crane and so an alternative method was needed. Enerpac proposed to use a push-pull system for the wheel construction.
The concept of the Push-Pull system for the wheel assembly is straightforward enough. Located at the base of the wheel, a pair of hydraulic grippers pushes the wheel forward, effectively rotating it. The push grippers are then released and pulled back into position using hydraulic cylinders. The push-pull operation is then repeated.
The simplicity of operating Enerpac’s system belies the complexity of the engineering underpinning it. Implementing the concept for ‘Ain Dubai’ meant working to significant project constraints. Aside from the environmental conditions, these included rotational loads up to 2,572 tons – the largest load ever handled by such a system, highly accurate control of wheel rim movement, and accommodating the system within limited space constraints. Also, for the first six months of the wheel’s construction the entire load of the part completed wheel would be borne by the system.
The wheel segments are welded together as each new segment is added. Ensuring the welding process could be completed smoothly relied on precise positioning of each new segment by the Enerpac system. Using precision hydraulic control, the Push-Pull system was able to bring the wheel rim within a few millimetres of the previous rim, and hold it there, to enable the two segments to be welded together. Once the weld was completed, the Push-Pull system was used to progressively feed the wheel segment through, enabling the next segment to be added.
The Push-Pull system is powered and operated by a central hydraulic power unit (HPU). The HPU’s diesel engine, main control panel, safety PLC and tank with hydraulic oil are
controlled by PLC and laptop computer.
In addition to the push-pull system, Enerpac is supplying the drive and control system for the ‘Ain Dubai’. The company has supplied hydraulic drive and control systems for large observation wheels including the London Eye and Las Vegas High Roller.