Water makes a comeback

When a pork processing plant in Denmark recently installed a new hydraulic
cutting machine, no one worried that hydraulic oil would leak into the meat. The
company's seeming lack of concern over contamination wasn't misplaced, however.
Its new machine doesn't use hydraulic oil. Instead, it operates off tap water.

For the machine's designer, the decision to go with water hydraulics, rather than more widely accepted alternatives, is at the cutting edge of a self-renewal trend. Throughout the long history of hydraulics, the oil vs. water debate has intermittently resurrected itself, most recently with the introduction of a raft of effective, new water hydraulics components.

In the past, water-based systems have earned only a grudging respect from the engineering community. During the last half century of its 200-year history, water hydraulics has been viewed mostly as a curiosity-an outdated technology driving creaky machinery.

No pork barrel. But advances in water-based components are changing that. At SFK Meat Systems in Denmark, the decision to go with water hydraulics was one based on new technical criteria, rather than traditional beliefs. The machine's engineers selected Danfoss' NESSIE water hydraulics system over more traditional alternatives, such as pneumatics or electric motors. "We moved away from air-driven machinery because of the cost of running it and the noise," explains Erik Petersen, manager for trade and service at SFK Meat Systems, designer of the new machine.

Pneumatic versions, Petersen explains, typically exhibited noise levels of 88-89 dBA, compared to as little as 80 dBA on the water hydraulic system. Similarly, SFK steered clear of electric motors, because of the large package size needed for the saw's 3-hp requirements.

Experts expect food processing to be one of the biggest new applications for water hydraulics. Unlike oil-based hydraulics, water systems present no potential for contamination of food. As a result, they also hold appeal for the pharmaceuticals industry.

The new hope for water hydraulics extends into a number of other areas. Hauhinco Maschineenfabrik, Sprockhovel, Germany, has sold water-based systems to a variety of new customers, including a German luxury-car manufacturer, which uses it in welding robots. Hytar Oy, Tampere, Finland, has applied its water-based systems to seawater ballast pumps, diesel emission-control systems, and water cutting power packs for the paper industry.

Water hydraulics fell out of favor early this century when engineers developed oil-resistant seals. From that point on, oil hydraulics dominated. Water, meanwhile, came to be thought of as a cost- ly alternative with inherent technical problems.

That was then. That characterization was accurate-at one time. Water presented a host of tough technical challenges for engineers. Among them: low viscosity, poor lubricity, corrosiveness, freezing, and fluid loss at high temperatures. As a result, component manufacturers found it difficult to maintain seal integrity. They also struggled to design state-of-the-art pumps and valves and to prevent erosion of internal surfaces. Though most of those problems were solvable, the cost of the solutions was, in many cases, three to four times as high as those of oil hydraulics.

That's why, for the past 40 years, water hydraulics has centered on a select few

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