Performance and Response of packages in High-Pressure Hydraulic Systems|News|UNPChemicals

January 26, 2026

Performance and Response of packages in High-Pressure Hydraulic Systems

In the fields of modern industry, engineering machinery, and aerospace, hydraulic systems are evolving towards higher pressure, higher precision, and higher efficiency. As the working pressure of the system exceeds the 350 bar mark, the lubrication and protection capabilities of traditional hydraulic oils are facing severe challenges. As the core component determining the performance of oil products, the performance of hydraulic oil compound additives in extreme pressure anti-wear, thermal oxidation stability, and shear stability is directly related to the operating life and safety of equipment. This article will delve into the special requirements of high-pressure systems above 350 bar for compound additives and explore the key technologies for anti-wear mechanisms and shear stability control.

1. What is a hydraulic oil additive package?

Hydraulic Oil Additives Package is a concentrated mixture composed of various single additives (anti-wear agents, antioxidants, rust inhibitors, anti-foaming agents, metal deactivators, etc.) formulated in specific proportions. Its core function is to compensate for the inherent deficiencies of base oil in performance and endow hydraulic oil with comprehensive protection capabilities under extreme operating conditions.

As a professional supplier in the lubricant additive industry, UNPChemicals focuses on the research, development, and production of high-quality, high-performance hydraulic oil additives. We provide a full range of solutions tailored to different equipment materials and operating conditions. Our product portfolio includes:

High-Zinc Hydraulic Oil Compound UNP AH502A: Suitable for traditional hydraulic systems with extremely high requirements for extreme pressure and anti-wear performance, providing excellent load-carrying capacity.
Low-Zinc Hydraulic Oil Compound UNP AH502B: Balances anti-wear performance and corrosion protection of copper components, suitable for systems containing copper components.
Zinc-Free Hydraulic Oil Compound UNP AH502C: Specifically designed for high-precision hydraulic systems with strict environmental requirements or sensitivity to silver and copper plating, to avoid the risk of metal corrosion.

These compound products have all undergone strict bench tests and real vehicle verifications, and can meet the production requirements of hydraulic oils with different specifications from L-HM to L-HV.

2. Special Requirements for Compounding Agents in Systems Above 350 bar

High-pressure operating conditions above 350 bar are fundamentally different from normal operating conditions. Under high pressure, the contact pressure of the friction pairs inside hydraulic pumps (piston pumps, vane pumps) increases exponentially, and the local temperature rises sharply, which imposes the following stringent requirements on the compounding agent:

Extreme pressure and anti-wear performance (EP/AW)

Under a high pressure of 350 bar, the oil film is extremely prone to rupture, leading to direct contact between metal surfaces. The compound additive must possess excellent extreme pressure and anti-wear properties, capable of instantly forming a high-strength protective film to prevent scuffing, seizure, or sintering of the pump body. This requires the sulfur-phosphorus (S-P) type extreme pressure and anti-wear agent in the compound additive to have a precise ratio, which can react quickly without causing excessive corrosion due to over-activity.

Excellent thermal oxidation stability

The heat generated by fluid shear due to high pressure will increase the oil temperature and accelerate oil oxidation. The sludge and varnish produced by oxidation will clog the servo valve, causing system control failure. Therefore, the compound additive must contain highly effective antioxidant components (such as the combination of hindered phenols and aromatic amines), which can inhibit the free radical chain reaction for a long time and extend the oil change interval.

Excellent filtration and hydrolytic stability

Modern high-pressure systems are generally equipped with high-precision filters (3μm - 10μm). Inferior compounding agents may precipitate gum after high-pressure shearing or contact with water, leading to filter blockage. In addition, in a humid environment, compounding agents must have good hydrolytic stability to prevent the decomposition and failure of additives, while maintaining the anti-emulsification ability of the oil to ensure rapid separation of oil and water.

Good compatibility with sealing materials

Under high pressure, the seal is subjected to a huge extrusion force. The compounding agent must not contain components that cause excessive hardening or swelling of sealing materials (such as nitrile rubber and fluororubber), otherwise it is very likely to cause hydraulic oil leakage, resulting in serious safety accidents.

3. Mechanism of Action of Antiwear Additives in High-Pressure Boundary Lubrication

In high-pressure environments above 350 bar, the lubrication state mainly transitions from hydrodynamic lubrication to boundary lubrication . At this time, the viscosity of the base oil is no longer sufficient to support the oil film, and the chemical action of anti-wear additives becomes the key to protection. Its mechanism of action is mainly divided into the following three stages:

Physical adsorption mechanism (first protective layer)

At low pressure or during the start-up phase, the molecules of oiliness agents (such as fatty acids and esters) in the compound are directionally adsorbed on the metal surface through polar groups, forming a physical adsorption film. This film is bonded to the metal through van der Waals forces, which can reduce the friction coefficient and minimize minor wear. However, under a high pressure of 350 bar, a simple physical adsorption film is prone to desorption and failure, requiring a stronger chemical film for support.

Chemical reaction mechanism (core protective layer)

When pressure and temperature reach the critical point, the physical film ruptures, and anti-wear agents (such as ZDDP, zinc dialkyldithiophosphate) undergo tribochemical reactions with the metal surface.

Decomposition and Deposition: ZDDP decomposes at high temperatures, releasing active sulfur and phosphorus.
Protective film formation: The active elements react with the iron-based friction pair to form a chemical reaction film composed of iron sulfide (FeS) and iron phosphate (FePO4).
Working Principle: This chemical reaction film has a high melting point and low shear strength. Under high pressure, it allows relative sliding between friction surfaces while withstanding large vertical loads, thereby preventing direct contact and cold welding of the metal substrate. UNPChemicals'UNP AH502A precisely utilizes this mechanism, optimizing the zinc salt structure to enable faster film formation and a tougher film layer under high pressure.

Deposition Film and Repair Mechanism (Long-Term Maintenance)

Some high-end compound additives also have repair functions. During the friction process, the colloidal substances produced by the decomposition of additives will deposit in microscopic wear pits, filling them up and making the friction surface smoother, further reducing friction losses.

4. Shear Stability Control of Hydraulic Oil Compounding Agents under High Pressure

In high-pressure hydraulic systems, when hydraulic oil flows through pump outlets, valve ports, and orifices, the flow velocity is extremely high, generating strong mechanical shear forces . For multi-grade oils with viscosity index improvers (VII) added (such as L-HV low-temperature hydraulic oil), shear stability is a key indicator determining whether the oil can be used for a long time.

Hazards of Shear Failure

If the anti-shear ability of the viscosity-increasing components (such as polymethacrylate PMA or olefin copolymer OCP) in the compound formulation is insufficient, their long-chain molecules will break under high-pressure shear. The breakage of molecular chains will lead to a permanent decrease in the kinematic viscosity of the hydraulic oil.

Consequence 1 : A decrease in viscosity leads to a thinner oil film, a sharp reduction in anti-wear ability, and accelerated pump wear.
Consequence 2 : The viscosity index decreases, and the viscosity of the oil at high temperatures may fall below the minimum value required by the equipment, leading to a decrease in volumetric efficiency and even causing cavitation.

Control technology for shear stability

To address high-pressure shearing above 350 bar, the development of compound agents needs to start from the following two aspects:

Select polymers with high shear stability : In the formulation design of compound additives, hydrogenated styrene-diene copolymers (HSD) or PMA with specific molecular structures should be preferentially selected. The molecular chain structure of these polymers is more compact, and their shear resistance is far superior to that of traditional OCPs.
Optimized compounding process: UNPChemicals employs a unique compounding technology of high and low molecular weight polymers in the production ofUNP AH502BandUNP AH502C. This "bimolecular" synergistic effect not only ensures a high viscosity index of the oil but also, when subjected to shear, only loses part of the non-critical molecular weight, maintaining the stability of the core viscosity index.

Test Standards and Verification

Common methods for evaluating shear stability include the ultrasonic shear test (ASTM D2603) and the diesel injector shear test (ASTM D6278). For oils used in high-pressure systems, it is generally required that the viscosity reduction rate be controlled within 10%-15% after a specified number of shear cycles.

5. Summary and Selection Recommendations

As the pressure of hydraulic systems advances towards 350 bar and higher levels, hydraulic oil compound additives are no longer simply a stack of additives, but rather a systematic engineering project involving physics, chemistry, and materials science.

Selection recommendations for high-voltage systems:

Identify the operating conditions: If it is a high-load plunger pump system, it is recommended to use UNP AH502A, which has a moderate zinc content and strong anti-wear properties.
Material of concern : If the system contains precision servo valves or silver-plated components, UNP AH502C must be zinc-free or low ash to prevent silver corrosion and valve jamming.
Environmental Factors: Under operating conditions with large temperature differences and frequent start-stop cycles, L-HV or L-HS hydraulic oils formulated with compound additives having high shear stability should be selected.

The Price of Hydraulic Oil Additives Package

The price of Hydraulic Oil Additives Package varies depending on factors such as brand, specification, composition, and sales channels. If you are interested in Hydraulic Oil Additives Package, please feel free to contact us.

Supplier of Hydraulic Oil Additives Package

UNPChemicals is a professional supplier of high-quality and effective Hydraulic Oil Additives Package. We offer several remarkable products, namely High zinc hydraulic oil additives UNP AH502A,Low Zinc Hydraulic Oil Additives UNP AH502B,Zinc-free Hydraulic Oil Additives UNP AH502C,etc.

High zinc hydraulic oil additives UNP AH502A are a type of chemical additive used in hydraulic oils that contain high levels of zinc dialkyldithiophosphate (ZDDP). ZDDP is a well-known anti-wear agent that also provides antioxidant, anti-corrosion, and anti-foam properties. The zinc in these additives plays a crucial role in forming a protective film on metal surfaces within the hydraulic system, thereby reducing wear and extending the life of the system components.

Low Zinc Hydraulic Oil Additives UNP AH502B are a class of advanced lubricant additives designed to enhance the performance of hydraulic oils with reduced zinc content.These additives are formulated to provide a balance of anti-wear,extreme pressure,and antioxidant properties,making them suitable for modern hydraulic systems that demand high performance with lower environmental impact.

Zinc-free Hydraulic Oil Additives UNP AH502C are a new class of environmentally friendly lubricant additives designed for hydraulic systems.These additives are formulated to provide the same level of performance as traditional zinc-containing additives but without the heavy metal content,reducing the environmental impact of hydraulic fluids.

Professional Lubricant Additive Manufacturer

UNPChemicals,aka Luoyang Pacific United Petrochemical Co., Ltd., focuses on the application and development of special lubricating grease additives such as MODTC, MODTP, molybdenum amide, thiadiazole metal deactivators, and phosphate esters. With nearly 30 products in seven series, including extreme pressure anti-wear additives and special grease additives, it is a global manufacturer of special lubricating grease additives and a national high-tech enterprise with great influence and leading role in the industry. If you are looking for Lubricant Additive or technical information, feel free to contact UNPChemicals.

Performance and Response of packages in High-Pressure Hydraulic Systems