What is the best material for hydraulic oil seal?

Introduction to Hydraulic Oil Seals

Hydraulic oil seals play a crucial role in hydraulic systems by preventing leakage and ensuring the retention of hydraulic fluids. These seals maintain system pressure and protect against environmental contamination, making them essential for the efficient and reliable operation of hydraulic machinery. However, selecting the right material for these seals is critical, as different materials offer varying levels of resistance to temperature, fluids, and mechanical stress. Understanding the trade-offs and compatibility of various seal materials is vital for ensuring optimal performance and longevity in hydraulic systems.

Materials Commonly Used for Hydraulic Oil Seals

The choice of material for hydraulic oil seals significantly impacts their performance and durability. Several materials are commonly used, each with unique properties and applications. These materials include acrylonitrile butadiene rubber (NBR), fluorocarbon rubber (FKM/Viton), and thermoplastic polyurethanes (TPU). Each of these materials offers distinct advantages and limitations, making it important to select the appropriate material based on the specific requirements of the hydraulic system.

Acrylonitrile Butadiene Rubber

● Advantages and Limitations

Acrylonitrile butadiene rubber (NBR) is one of the most widely used materials for hydraulic oil seals due to its excellent resistance to petroleum-based hydraulic fluids. NBR can operate effectively within a temperature range of -50°C to 120°C (-60°F to 250°F) and can withstand temperatures up to 150°C (300°F) for shorter periods, although this may shorten its service life. Despite its excellent fluid resistance, NBR is not resistant to weathering and is susceptible to degradation when exposed to ozone and sunlight.

● Suitable Applications and Compatible Fluids

NBR seals are compatible with petroleum-based hydrocarbons, mineral oils, diesel, fuel oils, vegetable oils, greases, HFA, HFB, and HFC hydraulic fluids, as well as dilute acids, alkali, and salt solutions at moderate temperatures. However, they are incompatible with highly aromatic hydrocarbons, ketones, acetic acid, strong acids, and glycol-based brake fluids. As a result, NBR is ideal for applications involving moderate temperatures and a wide range of petroleum-based fluids, making it a cost-effective choice for many hydraulic systems.

Fluorocarbon Rubber (FKM/Viton)

● Key Features and Benefits

Fluorocarbon rubber (FKM), commonly known by the trade name Viton, offers superior resistance to high temperatures and aggressive chemicals compared to NBR. FKM can operate within a temperature range of -40°C to 200°C (-40°F to 400°F), making it suitable for high-temperature applications. Additionally, FKM exhibits excellent resistance to weathering, ozone, and a wide variety of fluids, including synthetic hydraulic fluids and many organic solvents.

● Differences Between Type A and Type G FKM

There are two primary classes of Viton materials: Type A and Type G. Type A is more commonly used and offers a lower cost, while Type G provides enhanced compatibility with a broader range of fluids and improved resistance to weathering and ozone. The choice between Type A and Type G depends on the specific requirements of the application, with Type G being favored for more demanding environments.

Thermoplastic Polyurethanes (TPU)

● Specific Applications and Performance

Thermoplastic polyurethanes (TPU) are used for specialized hydraulic applications, particularly where bio-hydraulic fluids are involved. TPU seals offer excellent wear resistance, high resilience, and tear resistance, making them suitable for applications requiring durable and robust sealing solutions. Due to their compatibility with bio-hydraulic fluids, TPU seals are often used in environmentally sensitive applications where the use of biodegradable fluids is mandated.

Hydraulic Fluid Base Oils and Seal Compatibility

● Types of Base Oils and Their Impact on Seals

Hydraulic fluids are composed of various base oils that can significantly impact the performance of hydraulic seals. The American Petroleum Institute (API) classifies base oils into five groups based on their refining processes and properties. API Group I base oils are solvent-extracted, while API Group II and III base oils undergo hydroprocessing techniques, resulting in superior oxidation resistance and color stability. API Group IV base oils are polyalphaolefins (PAO), and Group V includes various synthetic and natural oils such as naphthenic mineral oils, polyalkylene glycol (PAG), and synthetic esters.

● Interaction Between Additives and Seal Materials

Base oils are often mixed with additives to enhance specific properties such as oxidation resistance, anti-wear characteristics, and viscosity index improvement. These additives can introduce additional interactions with seal materials, potentially affecting their performance. Understanding the compatibility between the selected hydraulic fluid and the seal material is crucial for ensuring optimal seal performance and longevity.

Predicting Fluid and Seal Material Behavior

● Methods for Assessing Compatibility

To predict the swelling or shrinkage behavior of a seal material in the presence of a specific hydraulic fluid, various methods can be employed. One common approach is comparing the aniline point of the hydraulic fluid to the aniline point of standard reference oils. The aniline point indicates the solubility of the oil in the elastomer and provides a useful indication of oil/seal compatibility.

● Importance of the Aniline Point and Elastomer Compatibility Index (ECI)

The Elastomer Compatibility Index (ECI) method offers a more accurate prediction of seal behavior. It involves comparing the behavior of a standard NBR compound in a range of petroleum-based oils to the behaviors of other nitrile compounds. By plotting the results on a graph, the Swelling Behavior (SB) of the compound can be determined. Knowing the ECI of the fluid and the SB of the seal material allows for the calculation of the expected physical interaction, enabling more informed material selection.

Selecting the Right Seal Material for Applications

● Factors to Consider in Selection

Selecting the optimal seal material for a hydraulic system involves considering several factors, including the operating temperature range, fluid compatibility, mechanical stress, and environmental conditions. It is essential to balance the material properties with the specific requirements of the application to ensure reliable and long-lasting seal performance.

● Guidance for New Builds and Maintenance Replacements

For new builds, it is advisable to start with commonly used materials such as NBR or FKM, unless the application has unique requirements or known fluid compatibility issues. Consulting with manufacturers and hydraulic seal repair experts can provide valuable guidance in selecting the most suitable material. For maintenance replacements, it is crucial to consider the impact of any changes in hydraulic fluid on the existing seals and seek advice from hydraulic seal repair manufacturers and suppliers.

NBR vs. FKM: Cost and Performance Considerations

● Cost-Effectiveness of NBR

NBR seals are generally more cost-effective than FKM seals, making them a popular choice for many hydraulic systems. Their compatibility with a wide range of fluids and moderate temperature resistance makes NBR a practical and economical option for many applications. However, their susceptibility to weathering and limited high-temperature performance can be a drawback in more demanding environments.

● Performance Benefits of FKM in Different Conditions

FKM seals offer superior performance in high-temperature and chemically aggressive environments. Their excellent resistance to a wide range of fluids, including synthetic hydraulic fluids and organic solvents, makes them ideal for applications where standard NBR seals may fail. While FKM seals are more expensive, their enhanced durability and broader compatibility can justify the higher cost in applications requiring high-quality hydraulic seal repair.

Consulting Manufacturers for Seal Material Selection

● Importance of Expert Guidance

Given the complex interactions between hydraulic fluids and seal materials, seeking guidance from hydraulic seal repair manufacturers and suppliers is essential. These experts can provide valuable insights and recommendations based on extensive research and field experience, ensuring that the selected seal material meets the specific requirements of the application.

● Steps to Ensure Optimal Seal Performance and Longevity

To achieve optimal seal performance and longevity, it is important to follow a systematic approach. This includes evaluating the operating conditions, understanding fluid compatibility, consulting with experts, and selecting high-quality materials from reputable hydraulic seal repair factories. Regular monitoring and maintenance of the hydraulic seals can further enhance their performance and extend their service life.


Selecting the best material for hydraulic oil seals involves a careful consideration of various factors, including fluid compatibility, temperature resistance, and mechanical properties. While NBR and FKM are the most commonly used materials, each offers distinct advantages and limitations. Consulting with manufacturers and hydraulic seal repair experts can provide valuable guidance in selecting the most suitable material for specific applications, ensuring optimal performance and longevity.

About Borise

Hangzhou Ruiwei Machinery Equipment Co., Ltd. is a professional sealing system supplier dedicated to the research, design, and production of excavator oil seals, hydraulic breaker oil seals, and oil seals for other construction machinery. The company's own brands include BORISE and WECKERSEALS. Borise is currently the seal supplier for most breaker brands in China. Adopting German technology in R&D and production engineering, Borise has developed high-resilience polyurethane oil seals and step seals with excellent wear and tear resistance, meeting the diverse needs of construction machinery sealing.What is the best material for hydraulic oil seal?
Post time: 2024-06-27 14:56:06
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