A key advantage of HEPR fluids is that they offer excellent oxidation stability and good corrosion protection. They also have good lubricity and aging characteristics, and a long service life. They offer good viscosity performance over a wide range of temperatures, from -30ºC to 100ºC. However, they are expensive and are incompatible with many seal and gasket materials.

When using biodegradable hydraulic fluids, there are several system design and operating factors that need to be considered, such as seal and hose material compatibility. The performance of pumps and motors are likely to be impacted. For example, most environmentally friendly fluids have higher specific gravities than traditional mineral oil based fluids, so pump-inlet conditions may need to be adjusted by having overhead reservoirs to ensure a positive inlet pressure, to maintain adequate suction and avoid cavitation.

Some biodegradable hydraulic fluids, particularly HEES and HETG types, are susceptible to water contamination, which degrades fluid properties. They readily absorb water and, if water remains in the fluid, will hydrolyze the fluid. In essence, the fluid will break down and lose lubricity, and acidity will increase. It is essential to monitor water content and acid levels closely in vegetable based and synthetic ester biodegradable fluids. Water-absorbent breathers can be used on reservoirs to limit water contamination, so that when the fluid level drops and outside air enters the reservoir, any moisture is captured.

Vegetable oil based biodegradable hydraulic fluids face problems at extremely low and high temperatures. They should not be used below the recommended temperature limits, as they tend to crystallise at low temperatures much faster than other fluids. They also tend to oxidise at high temperatures, which shortens fluid life. This is particularly true in mobile hydraulic systems.

Although standard filter elements are compatible with biodegradable fluids and filtration requirements are generally the same for mineral oil based and environmentally friendly fluids, in terms of particle sizes, filter change intervals may be different. HETG fluids that may have shorter service lives and a tendency to produce varnish and other contaminants may need to have larger filter elements.

Numerous types of hydraulic equipment are used in agriculture, horticulture or forestry applications. They include tractors, cultivators, harrows, de-stoners, broadcast seeders, seed drills, slurry spreaders, produce harvesters, balers, backhoe loaders, tractor-mounted forklifts, log fellers and feller bunchers, skidders and log harvesters.

Pathmaster Marketing estimates that the market for hydraulic fluids of all types was 610 thousand metric tonnes in Western Europe in 2015. Of this total around 13%, or 80 thousand metric tonnes were biodegradable fluids. Around 4% were HETG vegetable oil fluids and around 8% were HEES synthetic ester fluids. The amounts of HEPG polyglycol and HEPR polyalphaolefin fluids were very small in the hydraulic fluid market in Western Europe. The main countries in Western Europe that require or prefer the use of biodegradable hydraulic fluids in environmentally sensitive applications include Sweden, Norway, Finland, Denmark, Germany, Austria, France, the Netherlands, Belgium and the UK.

Agriculture, horticulture and forestry are particularly large users of biodegradable hydraulic oils, but these fluids are also used in other environmentally sensitive applications, For example, the UK Environmental Agency requires the use of biodegradable hydraulic oil in tracked machinery carrying out work on its behalf. Environment Agency policy stipulates that all companies

hiring tracked excavators to it will have to provide models that use biodegradable hydraulic oil.

According to the Environment Agency, “If the machines are using mineral oil and a leak occurs then long-term damage can be caused to the plants and wildlife in and around the watercourse. Biodegradable oil poses much less of a threat and minimises any damage that a spill could incur.”

The use of biodegradable hydraulic oils is increasing in other regions and countries, notably North America (the US and Canada) and Central Europe (Poland, the Czech Republic and Hungary). Biodegradable hydraulic oils are now marketed by the majority of leading suppliers of industrial lubricants. The sizes of the markets in these countries is more difficult to estimate, as reliable data is not collected or published in many countries.

Volumes of biodegradable hydraulic oils are increasing, slowly, world-wide, from a relatively low base. Pathmaster Marketing believes that the trend is likely to continue.

R D Whitby, Chief Executive




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