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Testing Validates Environmentally Friendly Hydraulic Fluids

When selecting fluid for ecologically sensitive applications, a few tests in appropriate categories can verify performance and the ecological effects of spills and leaks.

Operators seeking next-generation hydraulic fluids typically expect to find products with a low-impact environmental footprint that meets both current and future regulations without skimping on the high-performance requirements some systems need. As a possible solution, EnBio Industries offers its EnBio fluids, a polyalkylene glycol-based lubricant with five characteristics that differentiate it from other hydraulic fluids.

PAG fluids offer high film strength, high viscosity index (180 to 280), and good temperature stability. They are available in a wide range of viscosity grades, offer low volatility in high-temperature applications, and can be used in high- and low-temperature environments. Even though all PAG fluids share these advantages, EnBio brand fluids are readily biodegradable by OECD 301B, giving them higher environmental compatibility that other PAGs. EnBio fluids also have higher oxidation stability and pass saltwater corrosion testing, both resulting from our additive package.

The fluid’s high viscosity index (VI), which ranges from 195 to 204 across the product line, ensures fluid stability throughout a wide range of operating temperatures. Viscosity index indicates the change in an oil’s viscosity as the temperature increases or decreases. The higher this number, the lower the change in viscosity. Premium petroleum-based hydraulic fluids typically exhibit a VI of 100 to 140. Shearing and oxidation will lower this number and decrease viscosity, as will the ingress of a fluid with a lower VI or a contaminant like water.

Because EnBio products do not shear, viscosity will remain the same throughout the fluid’s life. Shearing can occur when operating conditions break and shorten a fluid’s molecular chains, which reduces the fluid’s viscosity. The strength of the bonds in EnBio’s PAG fluids prevents these chains from breaking, which gives the fluid its shear stability and extended operational life.

The fluid minimizes equipment wear, reducing wear during a vane pump test to more than 80% below other common types of hydraulics fluids on the market: mineral oils, natural esters, synthetic esters, and polyalphaolefin.

  • EnBio will not varnish or create sludge within a hydraulic system. This ensures that initial fills will run at peak efficiency without equipment breakdown due to sludge buildup. EnBio also will dissolve varnish left behind from non-PAG-based fluids, since all fluids with other compositions will create sludge and varnish. This will increase the level of efficiency in systems that previously used other types of fluid.
  • EnBio promotes a coefficient of friction between mating surfaces roughly half that of other fluid options. For example, mineral oils and esthers typically produce a coefficient of friction of 0.12 and 0.09, respectively, whereas EnBio produces 0.05. EnBio’s lubricity, a reference measure of a fluid’s ability to reduce friction, is the highest among hydraulic fluid types. All of these factors, plus its package of oxidation resistance additives, help make EnBio fluids last twice as long as mineral oil products and four to five times longer than bio-based products.

Converting to PAG Fluid

EnBio fluids are compatible with all hydraulic systems, although some minor changes might be required to switch from other fluids. EnBio Industries works with each user to review any changes needed and assist with the changeover.  Seals such as Buna–S and pure urethane have to be replaced if they are in continuous contact with the fluid.  Some equipment utilizing hydraulic fluids may have wet brakes, and if the pads are bonded with urethane glue, the potting compound has to be changed to epoxy.

The transition from a standard fluid—such as mineral oil, vegetable oil, or synthetic ester—is a simple process. Most systems are easy to drain and then purge with a small amount of EnBio to remove at least 95% of the previous product.

Testing Fluid Properties and Performance

To provide effective lubrication in a hydraulic system, EnBio fluids maintain critical viscosity at the relatively high shear rates they may encounter. It is important to minimize the non-Newtonian (viscosity dependent on shear rate or shear rate history) flow behavior of a hydraulic fluid to ensure adequate system lubrication. Several tests were conducted to verify these characteristics on EnBio MP46, formulated for a broad range of high-performance and environmentally sensitive applications.

A high shear rate viscometer was used to determine the non-Newtonian behavior of EnBio MP46 at 20°C, 40°C, and 80°C at shear rates up to 10 per sec. The results showed that, at the relatively high shear rates often encountered in hydraulic pumps, EnBio MP46 had essentially no viscosity loss.

It also is possible for a polymer to undergo molecular degradation, which results in permanent viscosity loss. An FISST (Fuel Injection Shear Stability Test) was conducted on EnBio MP46 according to American Society for Testing Materials (ASTM) standard D 3945. No viscosity loss was observed. These results showed that EnBio MP46 is essentially Newtonian and shear-stable.

To evaluate the lubrication properties of EnBio Mp46, it was compared with a hydraulic fluid formulated from phosphate esters, which exhibit excellent lubrication properties. One method of quantifying the relative lubricating properties of a fluid is to determine the coefficient of friction in a Ball-on-Disc test. The test results show that the coefficient of friction associated with EnBio MP46 was substantially lower than that of the phosphate ester fluid evaluated.

The following tests were performed to document EnBio MP46’s performance in pump applications. These tests showed EnBio MP46 to result in lower wear rates than standard mineral AW oil, as well as exhibiting greater wear resistance at high pressures under various use conditions.

ASTMD 2882—This is perhaps the most common standardized test to evaluate the relative performance rankings of a hydraulic fluid. Test results comparing two hydraulic fluids showed that a typical mineral anti-wear oil exhibited a wear rate of  0.223 mg/hr, whereas EnBio MP46 showed a value of 0.018 mg/hr.

Sundstrand Series 22 axial-piston pump—The total test duration was 225 hr., and the results showed no significant flow degradation (0.7%) over the full load period.

Sundstrand Series 20 cycled pressure piston pump—This pump was tested with EnBio MP46 at various pressures ranging from 2,500 to 4,500 psi over a period of 500 hr. After the test, visual inspection of the dismantled pump showed the valve plate to be in excellent condition, with no deposits in the grooves. The housing and components showed no evidence of cavitation, and the pistons showed no signs of wear and rotated freely on their slippers.

Enerpac HUSHH Pump—This test shows whether an oil will sludge, which can create wear. The pump’s first stage is a geroter pump operating at 500 to 600 psi. The second stage is an axial-piston pump operating at 7,000 psi. After testing with EnBio MP46, inspection of the pump showed no sludging or wear problems.

The most favorable tribological properties of a hydraulic fluid—i.e. its ability to lubricate—also can affect efficiency. The following table compares EnBio to Mobil DTE 15M and highlights the large increase in efficiency EnBio provides over the highest quality mineral oil products.

Although external factors such as contamination, cavitation, and heat caused by friction or internal leakage of a pump or motor can shorten a fluid’s life, EnBio has lasted twice as long as other fluids during actual tests on equipment. This is primarily because of its non-shearing qualities and greater oxidation stability. The following table demonstrates the longer life of EnBio fluids and their ability to resist oxidation.

Environmental Benefits

Working with Texas A&M, Penn State, the University of Nevada-Reno, and Edison College, EnBio Industries tests its products to determine their environmental impact in terms of three factors: toxicity, biodegradation, and bioaccumulation. Results suggest that the fluid actually helps contribute to plant growth, since it breaks down into helpful elements.


Toxicity is the sum of adverse effects or the degree of danger posed by a substance to living organisms. It generally is expressed as a dose response involving the quantity of a substance to which the organism is exposed and the route of exposure. It is particularly important to the survival of marine life but also to plants.  

OECD 202 and OECD 203 are tests currently applied to determine toxicity for products that are soluble in water. The test begins by dissolving the product being tested in water. Fish take a solution in through their gills, and at a certain concentration the solution becomes toxic to the fish. Ester- and PAO-based fluids are passing this test because they do not dissolve in water, but float on top. Because they do not form a solution that can pass through the fish’s gills, the result is a false positive. Mineral oil would also pass these tests but cannot be used because it is not biodegradable under OECD 301.

Phytotoxicity is a toxic effect by a compound on plant growth. Currently there are two promising phytotoxicity tests. Common duckweed is an aquatic species that is sensitive to toxicity. Duckweed can be used to test a compound with static, renewal, or flow-through methods. The latter two are especially useful for unstable compounds or samples. Seed germination and root elongation tests are versatile and can be tested in water, wastewater, sediment, and slurry.

Many recent activities in these areas suggest that phytotoxicity tests are a valuable part of ecotoxicology. Tests on different grasses have proven that EnBio is the only fluid that did not cause necrosis of the plant. It may dry the leaves if not washed but will not destroy the crown or roots, so the plant can regrow its leaves.


Biodegradation is the disintegration of a material by bacteria, fungi, or other biological means. It is now commonly associated with environmentally-friendly products, capable of decomposing back into natural elements. Biodegradable simply means a material can be consumed by microorganisms.

The ASTM standard, D6046-98a, classifies levels of biodegradability. To meet this specification a fluid must biodegrade at least 60% within 28 days. Primary biodegradation is a measure of the conversion by biological systems of the original organic material into different products. Ultimate biodegradation is the complete conversion by biological systems of the original organic material into carbon dioxide, water, and microbial biomass. EnBio fluids are the only PAG products that pass the biodegration test, OECD 301N, across the entire product line.


Bioaccumulation describes the build-up of chemicals in fish, plants, and other organisms. Through exposure in water or through the food chain, toxic chemicals can build up in these organisms over time. EnBio is classified as non-bioaccumulative based on independent testing.

Overall, transitioning to EnBio from any other fluid is an easy process. Operators can allow up to 5% of previous fluid to remain in the system without impacting performance, because remaining fluid generally will float to the top of a reservoir where it can be skimmed out. The company provides assistance and will train customer maintenance teams to make the fluid conversion quickly and efficiently.

Josh Green is director of business development at EnBio Industries Inc., Lake Worth, Fla. For more information, call (844) 438-3624, e-mail [email protected], or visit enbiousa.com.

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