Maximum Efficiency Hydraulic Fluids (MEHF) save operators money through improved equipment performance.
According to the August 2006 issue of Lubes’N’Greases, hydraulic oils were once relatively low-tech lubricants. Blended with modest levels of additives, they were considered inexpensive and 
interchangeable. Viscosity grade and price were the most important factors to consider when making a purchase, and users typically switched from a lighter viscosity in the winter to a heavier viscosity in the summer.
Because mobile hydraulic equipment has become more sophisticated in recent years, and reliable
hydraulic performance is a critical competitive advantage for manufacturers, hydraulic oil quality has taken on increased importance. In addition, hydraulic equipment end users are beginning to recognize the effects hydraulic fluid quality has on fuel efficiency and output. According to oil additive supplier RohMax, high viscosity index hydraulic fluids based on shear-stable viscosity index improvers have a significant effect on hydraulic fluid performance, saving operators money through increased equipment performance and efficiency.
“What’s been happening with hydraulic equipment in the field is that systems are being designed to be more efficient, more compact, with more pressure and speed,” says RohMax business development manager Doug Placek. “Fluids are subjected to higher temperatures. All this is being done to squeeze more efficiency from the design – and it places additional stress and performance challenges on the hydraulic fluids.”
RohMax identifies fluids that benefit overall hydraulic system performance as Maximum Efficiency Hydraulic Fluids (MEHF). “We’ve developed a very close relationship with major pump manufacturers, who have been very concerned about shear stability for a long time, about the increasing temperatures and pressures the oil has had to work under,” says Mike Zink, RohMax global business manager for hydraulic fluids. “The next step was to show how the fluid could contribute to hydraulic system efficiency – which is a major performance target for most equipment builders.
“Efficiency can be manifest in several ways,” says Zink. “Maybe it’s fuel cost, or equipment 
productivity, or for others, reducing emissions. In terms of equipment, it may mean getting more power output from a smaller unit. It varies from company to company and country to country. In North America, for example, end-users appear to be looking for increased productivity. In Europe, energy costs are a first concern, and in Asia, it’s emissions reductions. MEHF offers all of these benefits.”
“MEHF is not an additive package – that’s a common misconception – but rather it’s a performance-level definition for hydraulic fluids,” says Placek. “However, modern viscosity index improver additives allow a hydraulic oil to achieve the fluid viscometrics required to meet the MEHF performance level.
“To meet the performance level as it is defined, you’ll need a certain viscosity index and shear stability,” says Placek.“For example, with an ISO 46 grade fluid, you need to formulate to a viscosity index greater than 150 with very good shear stability. Such a fluid will be capable of delivering a 5 percent efficiency benefit or better. And the gains can even be pushed to two digits in a wide number of applications.”
Hydraulic fluid temperatures can change significantly over the course of a day, and they can vary in different pieces of equipment. Fluid viscosity increases when temperatures are low, decreasing flow and draining energy. When temperatures increase, fluid viscosity decreases and more fluid slips past the moving parts of the pump, decreasing equipment efficiency,increasing wear, reducing equipment life and contributing to higher operating temperatures.
Because high viscosity index hydraulic fluids effectively maintain viscosity through a wide temperature range, they maximize equipment efficiency. Tests performed by RohMax show that the higher a fluid’s viscosity index, the greater the efficiency of the equipment it is protecting. According to RohMax, increasing viscosity index from 100 to 150 provides a hydraulic fluid another 10 to 15 degrees C of operating temperature range. Higher viscosity index fluids are also serviceable in a wider range of applications.
AMSOIL Synthetic AW Series Antiwear Hydraulic Oils are the first synthetic MEHF hydraulic oils in North America. “The hydraulic oil we had in our product line – formulated by Alan Amatuzio and the guys in our lab – already met the basic MEHF requirements,” Kevin Dinwiddie, AMSOIL drivetrain and powertrain technical products manager, told Lubes’N’Greases. However, AMSOIL worked with RohMax to enhance the viscosity performance of AW Series Hydraulic Oils.
“In our case, we didn’t have to use as much viscosity modifier as fluids that are made with Group II or 
II+ base stock,” says Dinwiddie. “And now we are seeing even greater benefits than the others, even given the greater cost of PAO. “Because of gasoline prices being so high, everyone is interested in better fuel efficiency,”said Dinwiddie. “Using a better hydraulic oil goes straight to the bottom line, whether you’re an independent operator or someone with 50 trucks or a city fleet.”
AW Series Hydraulic Oils provide high viscosity indices and have been upgraded from efficiencies ranging from 3 to 4-1/2 percent to efficiencies ranging from 6 to 15 percent. The increased efficiency offered by AW Series Hydraulic Oils effectively lowers costs and increases productivity through fuel savings, increased production or both.
High viscosity index hydraulic fluids based on shear-stable viscosity improvers can have a significant effect on hydraulic fluid performance.
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