1. What is MEHF ?

MEHF stands for Maximum Efficiency Hydraulic Fluid, a performance level definition designed to give the operator confidence that the fluid in use has been formulated to deliver optimized energy efficiency over the entire spectrum of operating conditions.  MEHF products are formulated to minimize mechanical energy losses at low temperature, and also reduce internal pump leakage under high pressure/high temperature operating conditions.   MEHF products are characterized by high viscosity index (>150) and very good shear stability.

2. Why should I use MEHF?

MEHF delivers optimized pump efficiency which boosts power output and productivity for the equipment operator compared to standard hydraulic fluid options such as monograde HM fluids, engine oils and ATF.  Full benefits include:

• Energy savings per unit work of 5% or more, with a corresponding reduction in energy costs. Increased hydraulic power and reproducible equipment performance over a wider temperature range. Improved start-up performance at lower temperatures. Reduced need for auxiliary cooling. Reduced risk of overheating and consequent equipment shutdown.
• Elimination of seasonal oil change-outs.

3. Is MEHF a specification or standard required by OEMs?

No, MEHF is a performance level definition that can be used by OEMs, equipment builders, fluid marketers and operators to describe, request or promote a fluid that has been formulated to provide excellent pump efficiency.  MEHF performance is currently not a formal requirement in any OEM specification or regional standard.  Products which meet the MEHF performance level definition can be formulated to meet the major global specifications. Consult your preferred fluid supplier for their guidance on total product performance.

4. What is TOW?

TOW is an acronym for Temperature Operating Window developed by the NFPA (National Fluid Power Association).  It describes the temperature range over which a fluid can be used to meet OEM maximum-minimum viscosity requirements.  When fluid viscosity goes outside of the TOW due to cold ambient temperatures or demanding operating conditions, poor performance or pump damage is likely. Consult NFPA Recommended Practice T2.13.13-2002 “Fluid Viscosity Selection Criteria for Hydraulic Motors and Pumps” for full details on TOW, as well as a technique for selecting a hydraulic fluid viscosity grade for your specific equipment and operating conditions.

5. How do I calculate TOW?

Consult NFPA Recommended Practice T2.13.13-2002 “Fluid Viscosity Selection Criteria for Hydraulic Motors and Pumps” for full details on TOW.  The method has documented and organized the fluid viscosity requirements of the major global pump manufacturers which should be compared to the fluid operating temperature extremes in your equipment.  The information is plotted on a simple graph which then provides a fluid viscosity grade recommendation.

6. Where can I buy a product with MEHF performance?

MEHF is a new fluid performance level and hence is not currently (as of March 2005) widely promoted.  Contact your preferred supplier and inquire about products in their line that most closely match the MEHF requirements.  (See “Performance Benefits–Technical Data Sheet” section for details)  Most suppliers offer high quality fluids that will provide some or all of the critical MEHF features, most important are high VI (>150) in combination with good shear stability.

7. Has testing been performed in Vane pumps, Piston pumps and Gear pumps?

Yes, all pump manufacturers provide recommendations on pump selection based on the pressure, flowrate and work output demanded by the system.  Proper pump selection typically assumes that the fluid in use will enable the pump to work at >80% efficiency.  Pump manufacturers have tested all of their pump models using various fluids at several temperatures and provide recommendations on minimum viscosity requirements which are required to maintain reasonable efficiency. A number of technical papers have also been published which document the significant impact of operating viscosity on pump efficiency over a full range of temperature and pressure conditions in all pump types.  Additional details can be found in the “Supporting Technical Information” section.

8. Will my current hydraulic fluid deliver MEHF performance?

Consult with your supplier or review the product technical data sheet to see if the fluid properties include high VI (>150) in combination with good shear stability. Most suppliers offer high quality fluids that will provide some or all of the critical MEHF features.

9. Does MEHF also meet the requirements of other hydraulic fluid specifications?

The MEHF performance level does not conflict with other OEM specifications or regional standards.  A fluid that is formulated to meet any of the major global standards (such as those listed below) can also deliver MEHF performance.

Denison HF-O

Eaton Vickers M-2950-S

Cincinnati Lamb P68, P69, P70

ASTM D6158

DIN 51524

JCMAS HK

Please contact your preferred hydraulic fluid supplier for a review of specific product performance capabilities.

10. How is MEHF different from a standard HV or high VI fluid?

The ASTM and ISO definitions of the HV product grade, and the JCMAS definition of the high VI “W” grade, require that the fluid have a viscosity index of over 130.  These fluids are primarily designed to provide good low temperature start-up performance, which they do quite well.  The MEHF performance level has been developed to describe fluids that provide good low temperature fluidity AND excellent high temperature viscosity performance, such that pump efficiency is maximized at BOTH low and high temperature.

A standard HV or high VI product may offer some pump efficiency gains at high temperature, however, the MEHF definition requires the combination of high VI (>150) and good shear stability which insures optimized pump efficiency for increased power and productivity over the full range of operating conditions.