Fluid Handling

Compact, efficient, economical pumps and motors through fluid power

Fluid power technology is producing hydraulic pumps and motors that are more compact, efficient and economical than ever before.

By Sheila Kennedy

Fluid power technology is producing hydraulic pumps and motors that are more compact, efficient and economical than ever before. Engineered improvements are resolving performance limitations and fluid formulations are adapting accordingly. Global environmentalism and collaborative research are uniting government, industry and education in a common cause. As a result of new developments and those around the corner, hydraulic power systems are sure to gain a larger footprint throughout manufacturing.

Current advances: It’s recently become easier to move heavy loads without the high price tag of a radial-piston motor. Clever pressure-balancing techniques, heat control and other engineering strategies are increasing the efficiencies of gerotor/gerolor-type motors and allowing them to better compete with other technologies.

For instance, any small orifice or leakage path in a motor can cause efficiency problems that waste energy, which means wasted dollars. Eaton’s High Pressure 30 (HP30) disc valve hydraulic motor has a patent-pending two-piece balance ring that reduces leaks and drag that rob a motor of its efficiency. It eliminates the “potato chip effect” inherent when large disc-shaped surfaces are under pressure by ensuring the inner circle doesn’t deflect with the outer circle, instead staying mechanically close to the rotating internals. Previously, at pressure higher than 5,000 psi, gerotor/gerolor motors declined in volumetric and mechanical efficiency. The two-piece balance ring allows the motor to maintain efficiency or even surpass that of radial-piston motors.

“The HP30 is a 5,800-psi peak motor – the highest pressure rating in orbital motors – making it appropriate for industrial applications that run at very high pressure,” says Ross Hawley, Char-Lynn motors product manager for Eaton’s Hydraulics Operations. “The HP30 closes the gap with cam lobe piston products by providing high torque at high efficiency, while being more cost-effective and very durable.”

The motor is suited for conveyor as well as for mobile off-highway applications that require as much as 30,000 inch-pounds of intermittent torque. It provides high torque efficiency at startup, low pressure drop and smooth two-speed shifting.

Imported fluid technologies: The trend from Europe is toward biodegradable and water glycol fluids, which were popularized in the region because of more stringent environmental regulations. U.S. manufacturers selling in Europe are adapting to maintain market share and those companies will be ahead of the game if Congress chooses to pass similar laws here. Meanwhile, with environmentalism coming to the forefront globally, the new formulations already are being promoted as a feature or benefit of some fluid products sold in the United States.

Because fluid properties influence system efficiency, Eaton engineers are designing products with less viscous fluids in mind (e.g. water glycol). “Applications concerned with flammability of mineral oils are running water glycols for fire resistance,” says Hawley. “Water-soluble or biodegradable fluids are favored for their ecologically responsive properties in other applications. Fluid companies are using different chemistries to meet the needs of the industry.”

Depending on the system and application, certain hydraulic fluids may reduce the maximum permitted speed and pressure, promote excessive wear or shorten equipment life. Engineers must remain cognizant of the product ratings and make sure the selected fluid meets the requirements of the application.

Visionary change: Expect great things from the multimillion-dollar Engineering Research Center for Compact and Efficient Fluid Power. The Center’s inaugural conference, hosted at Georgia Tech in April, 2007, introduced projects that focused on efficiency, compactness and effectiveness. For instance, one project is investigating whether nano-texturing might produce substantial reductions in viscous and volumetric losses in fluid power systems. The first texture to be investigated involves nano-encapsulated air pockets to reduce the viscous pressure drop along lines. A second involves nano-dimpling to reduce leakage and increase the load carrying ability of sealing and bearing surfaces.

Another project targets optimized engineered fluid by studying the affect of fluid composition on the low-speed and starting efficiency of hydraulic motors. This includes lubricants formulated with boundary film-forming polymers and zinc-free boundary lubricants, including carbon nanotubes.

The Center’s vision is to generate fluid power technology that’s compact and efficient and, ultimately, to reduce our economy’s petroleum consumption and pollution. The research and education programs are made possible by a grant from the National Science Foundation, contributions from industry partners and universities, and help from the National Fluid Power Association.

E-mail Contributing Editor Sheila Kennedy, managing director of Additive Communications, at Sheila@addcomm.com.

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