Power packs

There is a belief both inside and outside engineering that, simply because hydraulics and pneumatics have been around for a long time, they are not 'modern' technologies. It is, however, an aspersion that Ian Morris, chief executive of the BFPA (British Fluid Power Association) refutes utterly. "The perception seems to be that, if it's not electrical or electronic, then it's not worth talking about. But that's very far from the truth," he insists. Morris, himself a mechanical engineer, concedes that you won't find step changes in technology to match the electronics sector, but points to an impressive evolution that makes the capabilities of today's fluid power very different to those of just a few years ago. He cites the integration of electronics into both hydraulic and pneumatic systems, massive improvements in manufacturing techniques and far better filtration systems as among the key enablers. Those, he argues, have together fostered not only better precision of control on demand, but also far greater power transmission from smaller footprint units, with increased efficiency, reduced waste and less pollution (including noise pollution). And he adds that maintenance, too, has been transformed, as electronics in cylinders and valves, connected via CANbus, provide for real-time visibility of contamination, as well as pressure and flow performance. Those, in turn, provide for predictive maintenance, with service scheduled when it's needed, not simply according to hours run or in response to breakdowns. "Hydraulic excavators today look much the same as they did 40 years ago, but they're completely different, in terms of their functions performed, power transmitted and noise," muses Morris. "They also use less energy; they're more efficient; and the environment is much better protected. And those parameters are still improving with each new model, as drive pressures increase and more sophisticated monitoring and control systems are added." Of course, he's right, but shaking off the old image remains tricky. Hence the troubling shortage of what Morris describes as 'hybrid' technicians and engineers – those capable of spanning electronics and mechanical engineering. "Engineers with this combination of skills are being trained, and in large numbers," he says. Indeed, the BFPA has a substantial CETOP (European fluid power committee) accredited training programme. "But the fluid power industry needs more multi-talented engineers, capable of getting the best out of these increasingly complex technologies." Rattle some cages For Alex Tatlow, technical director of fluid power specialist Group HES (which includes Branch Hydraulic Systems), it's about helping engineers to understand the key roles of hydraulics and pneumatics – and the challenging opportunities. He points to a recent partnership with servo-hydraulic simulation firm Servotest Testing Systems, which involved the development of a 2MW power pack to drive an earthquake simulator for the Indian Nuclear Research facility. This was a major project. We're talking about a pack delivering 3,000 l/min flow to perform tests on samples up to 100 tonnes, with a maximum, short-term requirement of 10,000 l/min, using banks of accumulators. To ensure delivery on-time and to budget, Branch took the decision to design the power unit around off-the-shelf equipment. However, the team had to consider two critical requirements – modularity and space limitations, both in transit and at the plant. "An open air container is costly and risks component corrosion damage at sea," explains Tatlow. "So, with the 10,000 litre tank assembly module measuring 2 x 2 x 3.5m, we had to ensure that it would fit through the doors of the container vessel." Branch designed and built 14 modules plus pipework in Gloucester, including the boost pump and three cooling sets. "This specification gave us the perfect opportunity to cut our teeth and prove our capability, taking everyday component parts and customising them to build one power pack." Plus points for hydraulics - Power density: like-for-like, hydraulic pumps and motors are an order of magnitude smaller than electric equivalents. - Inertia: the mass of moving parts in hydraulic equipment is negligible, whereas the rotating element of an electric motor constitutes 50% of its mass. - While electric motors can out-perform hydraulics on rotary motion, when it comes to linear motion, cylinders achieve efficiencies of more than 99%. - Unlike electrical equipment, hydraulic systems are very effective in load holding and starting off under high torque. - Hydraulic systems are generally more robust and resilient in harsh environments.