The different types of eco-friendly hydraulic fluids
Eco- friendly hydraulic fluids - are critical for applications where there are risks of leakage or spillage into the environment. Environmentally sensitive applications will benefit from the use of biodegradable fluids which will not damage the environment even when the oil line is ruptured. There are four basic types of biodegradable fluids that can be applied to a specific application and operating condition. When making a choice for the appropriate fluid to replace traditional petroleum-based fluids, it is important to consider its different chemistries, interaction with seal materials and other system components. The four types of biodegradable fluids are as follows:
HETG fluids – hydraulic environmental triglyceride is derived from vegetable and animal oils. The most common sources of these fluids are soybean, sunflower and rapeseed. In order to increase their natural viscosity at 35 mm2/40oC, they frequently contain soluble thickeners. HETG fluids have many advantages because they are highly biodegradable and non-toxic with excellent anti-corrosion properties and lubricity. However, HETG fluids have their drawbacks when used in high temperature operations. They can cause quick ageing, rapid oxidation and extreme thickening and gumming. In addition, the fluids are susceptible to water contamination that can result into hydrolysis and an increase in total acid number. At low temperature, the fluid can thicken and gel which can compromise machine performance.
HEES fluids – hydraulic environmental ester synthetic is water insoluble synthetic esters that are derived from either petroleum or rapeseed oil feedstock. The petroleum source combines organic acid and oil while the vegetable source combines fatty acids and alcohol. HEES fluids are available as unsaturated, partially saturated and fully saturated but the fully saturated version offers the best performance for a higher price. HEES fluids offer high thermal and oxidative stability with good fluidity at low temperatures. On the other hand, they also have drawbacks because the fluids can hydrolyze in the presence of water and require special system design requirements. Like HETG, HEES fluids are miscible with mineral oil which can hurt its biodegradability.
HEPG fluids – hydraulic environmental poly glycol are biodegradable based on the ratio between propylene and ethylene oxides. The higher the molecular weight of the fluid, the lower is its biodegradability. There is a broad range of viscosities with an operating temperature range of 20oC to 80oC. However, HEPG fluid also requires special design systems and they can be incompatible with polyurethane seals. Pumps and motors may have to be de-rated when used with HEPG fluids. On the other hand, HEPG fluids have their advantages in excellent oxidation stability and good corrosion protection, good lubricity, aging characteristics and long life. Good viscosity performance is possible over a wide temperature range.