High-Zinc, Low-Zinc or Ashless? What Actually Decides Your Anti-Wear Hydraulic Oil

Selecting the wrong zinc content in anti-wear hydraulic oil is a common trigger for the premature failure of high-pressure piston pumps. If a system with bronze valve plates comes into long-term contact with high-zinc oil, corrosion spots can develop into deep grooves within a few months; conversely, using ashless oil in ordinary vane pumps may lead to insufficient anti-wear performance. The correct choice among high-zinc, low-zinc, and ashless hydraulic oils depends keyly not on price, but on the material composition of the pump.

What is Anti-Wear Hydraulic Oil?

Anti-wear hydraulic oil is primarily used in heavy-duty, medium-pressure, and high-pressure hydraulic systems. It ensures proper lubrication for friction pairs in oil pumps, hydraulic motors, control valves, and hydraulic cylinders under high-pressure, high-speed, and severe operating conditions, thereby reducing wear. In addition, it rapidly separates water mixed into the oil to prevent rust on metal surfaces. Common anti-wear hydraulic oils are categorized into zinc-containing and ashless formulations.

What is the difference between high-zinc, low-zinc, and ashless hydraulic oils?

High-Zinc Type: The core additive of zinc-containing types is ZDDP (zinc dialkyldithiophosphate), with a zinc content of > 0.07%. It forms a zinc-sulfur-phosphorus reaction film on metal surfaces to provide anti-wear protection.

 

Low-Zinc Type: The zinc content is below 0.03%. Its anti-wear performance is slightly weaker than that of high-zinc oil, but its comprehensive performance (such as hydrolytic stability, filterability, and compatibility with seal materials) is relatively better, balancing a certain level of anti-wear capability with versatility.

 

Ashless Type: Free of zinc and other metal salts (total metal content < 0.01%). Its advantage is that, containing no zinc element, it will not react with silver-plated components. This is because many components, such as valves, use silver-plated materials; zinc will undergo a displacement reaction with silver, replacing the silver and causing component damage.

 

Chorus can provide various lubricant additives for the lubricant industry, including ZDDP, at affordable prices. Inquiries are welcome.

Performance Comparison of Anti-Wear Hydraulic Oils

Performance	High-Zinc	Low-Zinc	Ashless
Anti-wear / Extreme Pressure	Excellent	Good	Fair / Limited
Thermal Stability	Poor	Good	Excellent
Hydrolytic Stability	Poor	Good	Excellent
Corrosiveness to Copper / Bronze	Corrosive	Slight	Non-corrosive
Filterability	Poor	Good	Excellent
Environmental Impact / Waste Disposal	Poor	Moderate	Excellent
Relative Cost	Low	Moderate	Relatively High

 

How to Select Anti-Wear Hydraulic Oil?
 

 

The single core variable in selecting anti-wear hydraulic oil is friction pair materials.

Choose high-zinc for all-steel equipment to save costs, choose low-zinc as a transition option when non-ferrous metals are a concern, and choose ashless for precision, heavy-load, and high-humidity applications.
 

Friction Pair	Recommended Type	Reason
Steel–Steel	High-Zinc / Low-Zinc (Zinc-Containing Ash Type)	High anti-wear requirements; zinc-type oils are more likely to pass bench tests.
Steel–Copper (Bronze Valve Plate)	Ashless	ZDDP can corrode bronze; high-zinc oils may fail piston pump bench tests.
Steel–Steel (General Applications)	Low-Zinc / Ashless	Good general compatibility and a wider margin for correct selection.

 

High-Zinc Hydraulic Oil
Offers outstanding anti-wear and extreme pressure performance (forms a Zn-S-P reaction film on metal surfaces, providing high load-carrying capacity and wear reduction), excellent protection for steel-on-steel friction pairs (vane pumps), and high cost-effectiveness.

 

However, it causes corrosion on non-ferrous metals such as copper, silver, and brass (e.g., piston pumps with bronze valve plates). It lacks sufficient thermal stability and hydrolytic stability; under high temperatures or contaminated environments, it easily generates metal salt deposits, which can clog filter elements and cause valve sticking.

Suitable for general-purpose applications with all-steel friction pairs, such as standard medium-to-high-pressure hydraulic stations, CNC lathes, injection molding machines, and hydraulic presses under stable operating conditions without precision non-ferrous metal components.
 

Low-Zinc Hydraulic Oil
Provides slightly weaker anti-wear performance than high-zinc oil, but achieves a more balanced performance in hydrolytic stability, filterability, and seal compatibility. By reducing the dosage of ZDDP and supplementing it with amine antioxidants and metal deactivators, it balances anti-wear capability with versatility.

Application: Suitable for equipment with certain non-ferrous metal corrosion requirements where zinc is not strictly prohibited, serving as a transitional choice between high-zinc and ashless formulations. For example, high-temperature, high-pressure continuous-duty gear pumps.
 

Ashless Hydraulic Oil
Ashless lubricants are completely zinc-free. They offer excellent anti-wear performance, meeting the demands of medium-to-high-pressure systems. They feature outstanding anti-oxidation, anti-hydrolysis, and demulsibility properties, are less prone to sludge formation under high temperatures, and provide good filterability without clogging precision filter elements.

They cause no corrosion to non-ferrous metals such as copper, silver, and aluminum, and offer superior environmental friendliness. The main drawbacks are higher cost and demanding formulation requirements; however, waste fluid disposal costs are significantly reduced.

Application: Suitable for components containing copper/silver, precision servo systems, high-temperature heavy-duty equipment, high-humidity applications, and strict environmental compliance conditions. Examples include high-pressure piston pumps and hydraulic motors with copper/silver/brass components, high-temperature heavy-duty equipment like metallurgical rolling mills, and high-humidity operating environments such as marine vessels and offshore platforms.
 

Ashless = Sulfated Ash Content (SH/T 0301 / ASTM D874) < 0.01%
 

If you are currently selecting oil for a specific pump model or a mixed-equipment system, please provide the pump model, system pressure, operating temperature, and contact metal materials. The Chorus technical team will provide professional formulation recommendations based on your parameters.
 

Chorus specializes in providing a comprehensive range of hydraulic oil additive packages for the lubricant industry, including high-zinc, low-zinc, and ashless hydraulic oil additive packages, to flexibly meet diverse operating conditions. Welcome to contact us for customized hydraulic oil additive package solutions.