With numerous hydraulic oils available on the market, selecting the one that best suits your system can be a challenging task. Several factors should be considered when choosing the most suitable hydraulic oil.
Factors to Consider When Choosing Hydraulic Oil
As with many oils, the first set of factors to consider when selecting an oil are the operational limits of the system and the oil. Typically, OEMs can guide users accordingly in this area, as they pay attention to the operating temperatures, pressures of the system, as well as the required viscosity of the oil.
Next, they need to consider the environment in which they are working. Are there any possibilities of the oil entering waterways or the soil? In such cases, environmentally friendly lubricants should be used. They also need to determine if these oils will be exposed to harsher environmental conditions than regular ones. If this is the case, then they may consider utilizing synthetic oils instead of mineral oils.
Compatibility with Equipment and Seals
Most mineral hydraulic oils are compatible with seals and some metals. However, certain hydraulic oils are not. HFC fluids (Water polymer fire-resistant hydraulic fluids with water content >35%) react aggressively with tin and cadmium. As such, silicone rubber and Teflon are the materials utilized when these fluids are in use.
On the other hand, HFD fluids (water-free, synthetic fire-resistant hydraulic fluids) attack aluminum and aluminum alloys in the presence of friction stresses. Therefore, the only materials used with HFD oils are Viton and Teflon.
Due to the polar nature of environmentally friendly ester fluids, this causes significant swelling of conventional standard elastomers. On the other hand, Epikote and DD paints are resistant to HEPG (water-free, rapidly biodegradable polyalkylene glycols that are soluble in water), HFC, and HFD fluids to a certain extent. Therefore, the inside of tanks or other exposed surfaces should not be coated with these materials to avoid corrosion.
Environmental Regulations for Hydraulic Oil
Environmental lubricants are typically classified into three main categories:
Biodegradability – measure of the breakdown of a chemical (or chemical mixture) by microorganisms. This can be Primary (where there is a loss of one or more active groups that renders the compound inactive regarding that function) or Ultimate biodegradation (also known as mineralization, where the chemical compound is converted to carbon dioxide, water, and mineral salts).
Two additional operational properties that define biodegradability are inherently biodegradable (showing evidence of biodegradability in any test for biodegradability) and readily biodegradable (where a fraction of the compound is ultimately biodegradable within a specific time frame, as specified by a test method). Figure 9 shows a table of internationally standardized test methods for measuring biodegradability.
Aquatic Toxicity – This refers to the effects of a chemical on organisms that live in water and is determined using organisms representing three trophic levels: algae or plants (primary producers), Invertebrates (primary consumers or secondary producers), and vertebrates (secondary consumers).
Acute toxicity is determined by exposing fish to a series of concentrations of a chemical over a short period. The concentration that is lethal to 50% of the test fish is calculated and expressed as the LC50 value.
On the other hand, Chronic Toxicity covers a longer exposure time. It examines the effects on hatching, growth, and survival to determine the NOEC (No Observed Effect Concentration) values, LOEC (Lowest Observed Effect Concentration), or ECx values, where x is a percentage and the concentration of a chemical at which that percentage of the population shows some effect.
As seen in Figure 10, this is the list of OECD (Organization for Economic Co-operation and Development) Aquatic Toxicity Tests.
Bioaccumulation – this refers to the accumulation of chemicals within the tissues of an organism over time. Depending on the degradation rate of the chemical, this can lead to a buildup in the organism over time, ultimately resulting in adverse biological effects. The bioaccumulation potential of a compound is directly related to its water solubility. Figure 11 presents a summary of the bioaccumulation potential by base oil type.
Overall, when investigating the environmentally acceptable properties of lubricants, we can compare their behavior based on their base oil type, as shown in Figure 12.
Additionally, a comparison of their features by type is illustrated in Figure 13.
Several labelling programs provide guidance for EALS. These are summarized below in Figure 14.
