Addressing the demand for eco-friendly hydraulic fluids
The demand for eco friendly hydraulic fluids is growing to ensure that the environment will be safe but it should not compromise the performance of the medium. Environmentally acceptable hydraulic fluids that are being used today include HETG (hydraulic environmental triglyceride), HEES (hydraulic environmental ester synthetic), HEPG (hydraulic environmental poly glycol and HEPR (hydraulic environmental polyalphaolefin and related fluids. Each of these chemistries can be applied to a specific range of applications and operating categories with different interactions with seal materials and other system components. These interactions must be given attention when weighing the suitable replacement for petroleum based hydraulic fluids. It is also important to consider that eco-friendliness does not mean that the fluid is totally harmless to both humans and living animals; it is only less harmful compared to petroleum-based fluids.
What is HETG?
HETG hydraulic fluids are triglycerides derived from vegetable and animal oils the most common sources of which are soybean, sunflower and rapeseed. HETG fluids usually contain more soluble thickeners that increase their natural viscosity at approximately 35mm2/sec at 40oC. However, natural triglycerides have poor thermal and hydrolytic stability and oxidize rapidly but these limitations are improved with additives and chemical modifications including generic modifications on the seeds that are used as the base stock. HETG is biodegradable and non-toxic with excellent lubricity and anti-corrosion properties. Since HETG is derived from natural, renewable resources, there is never-ending supply. The drawbacks of HETG often make it undesirable to end users because it can be impacted by operational temperature that results into quick aging, rapid oxidation and extreme thickening and gumming. In addition, the fluids cost more than double the mineral oils and require special system design.
What is HEES?
HEES hydraulic fluids are synthetic esters derived from either petroleum or vegetable, typically rapeseed and oil feedstock. The fluids are available as unsaturated, partially saturated and fully saturated. Fully saturated offers the best performance but it also commands the highest price. HEES fluids have advantages like higher thermal and oxidative stability and better fluidity at low temperatures but it has more disadvantages. The hydraulic fluid is expensive and it requires special system design. It also hydrolyzes in the presence of water.
HEPG hydraulic fluids have the inherent fire-resistant characteristics and are offered in broad viscosity ranges. However, the fluids are incompatible with polyurethane seals and require special system design. Pumps and motors may need to be de-rated when used with HEPG fluids. HEPR fluids offer excellent oxidation stability and good corrosion resistance. The fluid also provides the advantages of good lubricity, aging characteristics and longer service life but it comes with a high cost.