In this issue:
32 MEDICAL PNEUMATICS
New twist on pneumatic muscles
38 HYDRAULIC VALVES
From the basic to advanced: selecting directional control valves
42 MOBILE HYDRAULICS
Mobile hydraulics troubleshooting
48 INDUSTRIAL HYDRAULICS
Hydraulic efficiency grows with variable speed drives
A simple path to higher efficiency
Everyone is for energy efficiency—as long as it doesn’t cost too much. Replace an incandescent light with a new LED bulb? Check. Find out an LED costs five times that of the old one? Maybe not so fast.
It’s no different with fluid-power systems. Engineers on a mission to improve efficiency can spend a lot of time comparing the benefits of high-efficiency pumps, VSDs and high-flow valves. But an often- overlooked way to make equipment more efficient is simply to change to a different hydraulic fluid.
Using the right fluid can noticeably improve overall machine efficiency and generate significant operating savings, according to Frank-Olaf Maehling, the global product manager for hydraulic fluids at Evonik Resource Efficiency in Darmstadt, Germany. He explained a trend among OEMs is to downsize circuits by using smaller components while operating at higher pressures. That increases power density, but it also puts greater demands on hydraulic systems and affects operating temperatures.
And that, in turn, affects fluid viscosity. It’s important to keep viscosity within a machine’s recommended limits (usually between 10 and 100 mm2/sec). However, basic monograde oils only maintain that viscosity within a limited temperature range. A viscosity that’s too high or low hurts mechanical and volumetric efficiency.
To address that shortcoming, engineers at Evonik have developed a portfolio of temperature-sensitive polymer additives, termed Dynavis, that improve the viscosity index (VI) of standard hydraulic fluids. Higher VI fluids maintain stable viscosity over a wider range of temperatures. These multigrade oils are thinner so components experience less friction and quicker start-up when cold; and are thicker for better control and less leakage when hot. While VI improvers aren’t new, they’re increasingly important for higher energy efficiency in hydraulic equipment.
One might expect such benefits in outdoor settings with varied conditions, but engineers find equally compelling efficiency improvements indoors. That’s because all the different components in complex systems rarely run at exactly the same temperature.
Switching to energy-efficient hydraulic fluids often pays off handsomely. Field tests by Evonik in equipment like excavators, skid-steer loaders and injection-molding machines demonstrate efficiency increases as high as 30%, depending on the task. That directly equates to fuel or electricity savings that can run into the thousands of dollars per machine every year.
“A top-tier hydraulic fluid formulated with Dynavis technology is priced slightly higher than a monograde hydraulic fluid,” Maehling admitted. “But significant savings are possible by spending a little bit more on fluid than just buying the cheapest available.”
Even considering the minor price premium, a growing number of equipment owners are recognizing the value of reliable operation and a lower total cost of ownership, he said. “Many classes of hydraulic equipment will benefit from a proper selection of the fluid.” Good candidates include construction; mining and agricultural equipment; marine onboard pumps and harbor cranes; and industrial presses, plastics processing machines, and pulp and paper manufacturing equipment.