Fluids That Keep You Moving

“Going green.” It’s not a trend. It’s a new way of doing business. Over the past several years, regulations have been passed globally requiring companies working on or near waterways to respect the wildlife who call their jobsite home. For manufacturers and operators of cranes, excavators and other mobile equipment, these restrictions are becoming increasingly important.

In terms of hydraulic systems, manufacturing has historically considered mineral oil to be a commodity. Fill the system, use the fluid, and throw it out. Rinse and repeat. Yet in an effort to meet regulations and gain contracts from green-minded clients, manufacturers are being forced to use biofluids that are significantly more expensive with little understanding about the differences in fluid types. Those differences mean everything when it comes to performance.

Standards for Biodegradability & Toxicity

To comply with environmental policies, biofluids need to meet standards for both biodegradability and toxicity. However, many fluid manufacturers have muddied these standards in such a way that biofluid users don’t always understand what they are buying.

Biodegradability can generally be broken down into two classifications – inherently biodegradable and readily biodegradable. All fluids are biodegradable (and so are you and I, as a matter of fact), meaning they break down within some undefined span of time. According to the U.S. Army Corps of Engineers, a hydraulic fluid is classified as readily biodegradable when 60% or more of the material is decomposed in 28 days.¹ When selecting a biofluid for use in an environmentally sensitive application, you should select a fluid that is readily biodegradable.

Simply because a fluid is biodegradable does not also necessarily indicate that it is non-toxic. According to that same classification, a hydraulic fluid is considered non-toxic if a specific ratio of the hydraulic fluid to water is used and less than 50% of the test organisms die within 96 hours.¹ Again, you will want to check the toxicity of a biofluid before selecting it for an application.

Biofluid Classifications

There are four major classifications of biofluids, each with their own distinctive characteristics and useful when given specific application requirements. It is imperative when selecting a biofluid that you understand the performance, temperature and longevity requirements of your system prior to making a selection.

1. HEPG (Polyglycols): These fluids may be water or oil based. They are very popular in applications where fire resistance is required, but those which are water based should be used with caution as they may not offer the same lubricity as an oil-based product.
2. HETG (Triglycerides): HETG’s are plant or animal based oils such as vegetable oil, rapeseed oil or sunflower oil. Many of these fluids do not perform well under high heat conditions, as the oil itself will begin to cook and therefore change its chemical composition. They do offer excellent biodegradability and rust prevention, but you must be cautious when using HETG fluids in high-heat applications.
3. HEPR (Polyalphaoelfins): Only a very limited range of PAO base fluids are readily biodegradable. These formulating restrictions lead to limited shear stability of the hydraulic fluid, meaning the viscosity may be progressively lost as it is run through a system.
4. HEES (Synthetic Esters): Synthetic esters have good biodegradability, but their performance can vary greatly dependent upon the ester type and base fluid used. Synthetic esters can be broken up into two categories – saturated esters and unsaturated esters.

Saturated vs. Unsaturated Synthetic Ester Fluids

It is unfortunate that many fluid manufacturers group unsaturated and saturated synthetic fluids together, just calling them ‘synthetic esters’ despite the major performance and longevity differences between the two types. The saturation of a fluid is based upon the chemical bonds within the fluid itself.