How to select the right fluid
A properly selected fluid meets the requirements of the various properties mentioned above in a balanced manner. Because identifying and interpreting all fluid requirements for a common user is difficult, Eaton has developed a full-fledged specification that cover requirements of hydraulic fluids and stipulate base stock requirements, physical properties, and performance requirements for both conventional and zinc-free hydraulic fluids, along with material compatibility with rubber materials. Fluids meeting this specification have been considered good quality hydraulic fluids. Most oil/ additive manufacturers follow Eaton’s specification and print the same on their catalogs and on oil containers, so that the common users can identify quality lubricants easily.
Eaton has developed fluid recommendations with for Eaton hydraulic products, such as “Hydraulic Fluid Recommendations,” which provides basic guidelines for selecting hydraulic fluid. The document provides viscosity recommendations and cleanliness requirements for Eaton hydraulic products.
Numerous lubricants other than conventional hydraulic fluids are used in hydraulic systems, such as motor oil, automatic transmission fluids, universal tractor transmission oil (UTTO), and super tractor oil universal (STOU). Some of these are formulated with mineral/ petroleum-base oils, while others are synthetic-base such as those using a polyalphaolefin (PAO) base. Most Eaton components are rated with these fluids.
While hydraulic pumps are generally designed to operate with mineral-base fluids, alternative fluids are sometimes used for applications where certain special properties are essential, perhaps even more important than hydraulic system performance.
For specific applications such as environmentally friendly and fireresistant applications, certain alternate fluids such as phosphate esters, polyol esters, polyether polyols, polyalkylene glycols, vegetable oil base fluids, water glycol, and invert emulsions, are sometimes used. For example, if fire resistance is critical, fireresistant properties may be the most important factor. Similarly, in environmentally sensitive applications, the focus may be on biodegradability and toxicity. Other fluid types, such as food-grade fluids and military specification fluids, are sometimes used in hydraulic applications.
Each alternative fluid may have certain advantages for the specified application, but their fundamental properties, such as lubrication, coefficient of friction, pressure viscosity coefficient, vapor pressure, specific gravity, and low temperature properties, may not be equivalent to those of mineral-base lubricants. Therefore, hydraulic components, especially pumps and motors may need to be de-rated to account for these adverse factors.