McRaes Global Engineering are proud to be part of the Lower Hatea River Crossing team, as part of the design team, through the construction phase and on-going maintenance with scheduled maintenance checks. We were invited by McConnell Dowell to tender on the design and build of the hydraulic system to operate the lifting span.
From the concept phase through to the final approval of construction has involved a lot of behind the scenes activity to get the concept accepted:
- Negotiate the price to an economically viable level for all parties
- Aligning H&S processes and Quality systems to fit contract requirements as well as fit our construction, testing and commissioning schedule with that of the other contractors.
The end result is almost un-noticeable from a bridge users perspective apart from the two very visible hydraulic cylinders. However, driving those cylinders is a hydraulic system custom designed and built for the task. Technically, the hydraulic system is fronted by the hydraulic cylinders with a bore of 320mm, a rod of 280mm diameter, a stroke travel of 8380mm and a weight of 8 tonnes each. These were made in Holland by Eaton in one of few plants in the world that can produce cylinders of this size and quality. Powering the cylinders is a hydraulic power unit with four 30kW motors driving 141cc/rev pumps. This provides a maximum flow of 800LPM.
The power unit was designed and built by McRaes Global in Whangarei. Included in the power unit are state of the art filtration and oil monitoring systems to ensure the oil is maintained at the correct cleanliness and temperature levels and system reliability optimised. Controlling the cylinder operation is a collaboration between hydraulic engineers and electrical engineers. A hydraulic valve manifold is installed in W1 pier adjacent to the cylinders with proportional valves to operate the cylinders through the phases of acceleration, full travel speed and deceleration to stop. These valves are computer controlled through a PLC provided and programmed as part of McKay Electrical’s contract. Connecting the power unit and the manifold are 300m of 50mm bore pressure line and 300m of 65mm bore return line. Joints are all welded SAE flanges – a total of more than 300 welds. Each pipe assembly was fabricated in our workshop and proof tested before being fitted to the system. High pressure hoses connect the valve manifolds to the cylinders.
All in all, it is a locally designed and built system that is world class that not only McRaes Global but the WDC and people of Northland can be proud to call theirs.