What is believed to be the largest hydraulic cylinder installed in the UK, manufactured by Hunger Hydraulic, is now in operation in London. A new 67 metre long bridge, designed to provide access to the Canary Wharf area of London’s Docklands, is operated by a massive single cylinder that lifts the north end of the 800 tonne bridge structure by 18,2 metres in order to provide a navigable passage beneath.
Hunger UK were first approached during 2001 by consulting engineers, Bennett Associates, who were looking for a means to lift the structure and were considering a single hydraulic cylinder as one of the bridge operating options. They were concerned that the single cylinder option flew in the face of conventional thinking where normally at least two cylinder operation would be provided to ensure the bridge structure would be supported in the event of the failure of one cylinder. However, Hunger engineers provided assurances that, providing the cylinder was designed to eliminate possible failure scenarios, the single cylinder option would have 100% integrity.
As a result, in February 2003, the operating system contractor, Kvaerner E & C UK Ltd, awarded a contract to Hunger to design and manufacture a single cylinder to lift the bridge structure.
Maintenance free bearings
The cylinder is a single acting 2-stage telescopic cylinder with ram diameters of 800 mm and 910 mm and a total stroke of 18,210 mm. The cylinder is vertically mounted in a pit below the north end of the bridge, supported on 360 mm trunnion bearings at the cylinder head. The smallest rod end is connected to bridge structure via a self-aligning bearing of 420 mm diameter. The bearings, manufactured by Hunger Maschinen, are maintenance free, requiring only periodical greasing to protect the mounting pin & bearing interface
Adjustable Sealing System
The cylinder design is a telescopic plunger type with the effective guide bearings located at the top end of each stage and smaller guide bearings on the plunger end of each stage to prevent excessive movement of the plunger ends inside the cylinder during operation. A ram stop is also included at full extension on each stage.
The ram sealing arrangement was of paramount importance to ensure safe cylinder operation under all operating conditions with provision to readily reseal the cylinder in the event of any leakage through the seals. This is catered for by using a sealing system incorporating the Hunger EVD externally adjustable sealing system. Each ram stage has a primary low friction seal with additionally a Hunger EVD seal, which acts as a backup to the primary seal to prolong the life of the sealing system. In the event of leakage from the primary seal, the EVD system can be manually operated to pressure load the EVD seal thereby providing an effective seal to prolong the period before a planned seal change can be made
Should a seal change become necessary, the complete sealing and bearing arrangement on each stage is accessible from the rod end and can be removed in situ without the need to remove the plunger rams from the cylinder tubes.
The cylinder is designed to support the bridge with generous safety factors. Under normal operating conditions the cylinder operating pressure is limited to around 110 bar from a bridge load of 565 tonne. However, the nominal design load, including snow & wind factors generates a cylinder design pressure of 140 bar. At this design pressure an additional minimum safety factor of 2.5 against material yield strength was applied to all stressed components. Finally, to confirm the integrity of the design, the cylinder was works pressure tested to 320 bar. For structural rigidity, the cylinder is designed to accommodate the nominal design load at full extension with a minimum buckling safety factor of 5 to1 applied
1030mm Diameter Cylinder Tube
Manufacture of the cylinder provided its own problems. To keep the cylinder diameters and weight to a reasonable level, high strength carbon steel tube material was used. The tubes, at up to 1,030 mm diameter, 45 mm thick and 10 metres in length, had to be fabricated from high strength flat plate, rolled, welded and heat treated. The raw tubes were then delivered to the Hunger works where all final machining and welding was carried out in house
Ceraplate Cerramic Coating
The two plunger rods are protected by Hunger CERAPLATE 2000 a well proven and enanced alternative to traditional galvanic coatings that provides a hard wearing and corrosion resistant protective layer. CERAPLATE is a multi-layer metal oxide coating, developed by Hunger for piston rods of hydraulic cylinders operating in hostile environments. The process involves an oxy-fuel flame sprayed sealing layer of nickel and chrome, overlaid with a plasma sprayed finishing layer of chrome and titanium oxides. The layer is finished by diamond honing and provides a 300µm thick layer with a hardness of around 1000Hv and a surface finish better than Ra 0,1.
The finished cylinder assembly weighs in excess of 40 tonnes and requires 11,000 litres of hydraulic fluid to extend both stages, fully opening the bridge in around 10 minutes.