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Regular and Zinc-Free (ZF) Hydraulic Oils

Zinc is a key additive in hydraulic oils, as well as in many other types of lubricants. It is primarily used as an anti-wear agent and antioxidant. Zinc-based additives are gradually consumed as they perform their protective functions. However, it is not metallic zinc itself that provides these benefits. Instead, a chemical reaction between zinc oxides and organic thiophosphoric acid produces zinc dialkyldithiophosphate (ZDDP) — a highly effective compound responsible for these properties.

Zinc-based hydraulic oils are widely used for several reasons. Under extreme conditions, a protective film of anti-wear additives (typically ZDDP) forms on bearing surfaces, shielding components from friction-related damage. These anti-wear additives are particularly effective under moderate to heavy load conditions.

The inclusion of ZDDP additives also helps prevent the formation of harmful acidic by-products, which can corrode equipment and degrade the lubricating properties of the base oil.

Another important advantage of ZDDP is its multifunctionality — it performs multiple protective roles simultaneously. Without ZDDP, multiple separate additives would be required, often in higher concentrations, increasing formulation costs.

The disadvantages of zinc-based additives include metal corrosion risks and environmental concerns. Excessive zinc content has historically led to the corrosion of certain yellow metals (such as brass and copper), as it chemically reacts with these materials. For this reason, some manufacturers explicitly state that zinc-based oils should not be used in certain components.

Additionally, ZDDP additives are non-biodegradable, and studies have shown that they are toxic to aquatic life, raising environmental concerns.

Despite these drawbacks, zinc-based hydraulic oils have a long history of proven performance and continue to be widely used. However, for applications requiring zinc-free alternatives, SUNOCO’s SUNVIS 800 ZF series offers excellent performance without the risks associated with zinc additives.