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Synchronised jacking system for precision tilting on research flumes

From flood prevention to resource protection, water represents one of today’s biggest ecological challenges. Tilting flumes are increasingly providing engineers with a key tool in the research of hydraulics and sedimentology. The latest products from Armfield offer the greatest levels of versatility, thanks to an automated jacking system supplied by Drives Lines Technologies Ltd.

People have intervened in the natural course and behaviour of rivers since before recorded history: to manage water resources, to protect against flooding or to make passage along or across rivers easier. Today, river engineering is a major area of study, as civil engineers look to understand flow dynamics, sediment transport and subaqueous debris flow.

Many areas of study require, or are enhanced by using, flumes (fixed length open channel water ways) with tilting capability, providing either positive or negative slope. Based in Ringwood near Southampton, Armfield has been designing and supplying flumes to hydraulic laboratories throughout the world for over 50 years. Today the company offers a full range of standard research flumes, in different working lengths, a variety of operating modes, and with full computer control and data logging capabilities.

Typically these flumes provide a high visibility glass sided flow channel, constructed in a rectangular prismatic section with a bed fabricated from stainless steel.

The most important aspect of a tilting flume is retaining the integrity of the working section to maintain tolerances and ensure both accuracy and repeatability. Achieving this requires an extremely rigid design to ensure almost no deflection regardless of load or tilt. The design of the tilting system is crucial in guaranteeing this stability.

Armfield recommends screw jacks, driven via distribution gearboxes, for its flumes, in order to achieve the best degree of repeatable accuracy and stability given the size and weight of the installation. On long flumes, a series of jack stations are used at different points along the length of the flume. These have to be carefully linked in order to avoid distortion of the main frame. Further, on these long flumes, and particularly where exceptional degrees of slope are involved, a pivot mechanism at each station ensures a vertical aspect to the jacks at all times.

To provide the critical jacking functionality on its new S60 modular tilting flume with lengths up to 30m, Armfield turned to Drive Lines. Expert in mechanical drive systems, Drive Lines represents leading mechanical power transmission manufacturers from across the world, and brings these components together to provide reliable, versatile and cost effective solutions.

The requirements were most demanding on the 15m version of the new flume, and required three screw jack stations interconnected by a geared drive. The system had to be capable of providing a positive slope of up to 1.43° and a negative slope of up to 0.29°, while maintaining a bed stability of better than 1mm at a 400mm water depth.

The 15m S60 flume has a pivot at one end, which means achieving the maximum slope entails raising the flume at the other end by 450mm. The jacking system supplied for the flume by Drive Lines comprises three jacking stations – the first at 5m from the pivot, the second at 10m and the third at 15m. With the flume working section measuring 800mm high by 600mm wide, filling to its maximum allowable depth imparts a maximum load in compression of 4 tonnes at each jacking station.

For the Drive Lines engineers, the key challenge was careful selection of the bevel gearbox ratios and motor speed to ensure even lift of the flume at each jacking station. At each of the first and second stations, Drive Lines installed two MJ3-GL screw jacks, while two MJ4-GL screw jacks were used at the third station. Manufactured by Grob Antriebstechnik, MJ series cubic screw jacks are ideal for use wherever controlled lifting, lowering and slewing are required. They can be installed singly, in pairs or as part of a multiple jacking system.

A 1.1kW motor connected to a Graessner PowerGear P-110-FL three-way gearbox is positioned between the second and third jacking stations, with power delivered to each of the three jacking stations via R+W EZ2/60 line shafts. Each shaft in turn drives a Graessner PowerGear P-110-L-123 gearbox at each jacking station, with the drive from the gearboxes to the twin jacks provided by further R+W EZ2/60 line shafts.

Robust, reliable and maintenance free, Graessner PowerGear bevel gearboxes offer angular torque transfer and torque distribution in single or multiple shaft configurations. They excel in applications where torque forces are high and space is limited.

The automated operator interface for the jacking system allows the user to introduce any incline target value that will be met automatically by the system. Electronic limit switches prevent movement beyond the maximum and minimum extent of travel.

Completely self-contained, the S60 tilting flume provides an essential tool for the hydraulics engineer, offering extensive demonstration capabilities in all aspects of open channel flow. Fitted with the Drive Lines jacking system to provide full electrical control of tilting, numerous S60 flumes have already been installed in educational and research facilities around the world, providing engineers with the tools they need to address some of the most pressing ecological challenges of our time.