What is the most common seal used in hydraulics?

Introduction to Hydraulic Seals

Hydraulic seals are critical components in hydraulic systems. They are primarily tasked with preventing fluid leakage, thereby maintaining the pressure necessary for the system to function efficiently. These seals are used in various applications, from industrial machinery to automotive systems, ensuring the smooth operation of hydraulically powered equipment. This article explores the most common seals used in hydraulics, with a particular focus on their types, properties, and applications.

Importance of Seal Integrity

● Consequences of Seal Failure

The integrity of hydraulic seals is paramount. Failure of these seals can result in leakage of hydraulic fluids, leading to a drop in system pressure and, consequently, a decline in performance. In severe cases, seal failure can cause total system breakdown, necessitating costly repairs and downtime. The consequences are particularly critical in high-stake environments like aviation, automotive, and heavy machinery.

● Factors Affecting Seal Performance

Various factors can compromise the integrity of hydraulic seals. These include high operating temperatures, fluid degradation, and the use of incompatible hydraulic fluids. When exposed to such conditions, seals can shrink, harden, crack, and lose elasticity. Identifying these factors early and using appropriate seal materials can mitigate the risk of seal failure.

Types of Hydraulic Seals

● Overview of Common Seal Types

Hydraulic systems employ different types of seals, each designed for specific applications. Primary types include piston seals, rod seals, wipers, and guide rings. Piston seals prevent fluid from bypassing the piston, ensuring a balanced pressure buildup. Rod seals keep fluid from leaking out of the cylinder, while wipers prevent contaminants from entering the system. Guide rings, on the other hand, maintain the alignment of moving parts.

● Specific Applications for Each Type

Each seal type has unique applications. For instance, piston seals are commonly used in hydraulic cylinders, while rod seals are essential in actuators. Wipers find use in harsh environments where external contamination is a concern, and guide rings are crucial in high-load applications to prevent metal-to-metal contact. Choosing the correct type of seal is essential for the system's efficiency and longevity.

NBR: The Most Common Seal Material

● Properties of Acrylonitrile Butadiene Rubber (NBR)

Acrylonitrile Butadiene Rubber (NBR) stands out as the most common material for hydraulic seals. Known for its excellent resistance to petroleum-based fluids, NBR operates effectively over a wide temperature range of -50°C to 120°C (-60°F to 250°F). This material is also relatively inexpensive, making it a cost-effective choice for many hydraulic applications.

● Advantages and Limitations of NBR Seals

The primary advantage of NBR seals is their compatibility with a broad spectrum of petroleum-based fluids, including mineral oils, diesel, and certain hydraulic fluids. However, NBR has its limitations. It is not resistant to weathering, making it unsuitable for outdoor applications where exposure to UV light and ozone could degrade its properties. Additionally, NBR's performance diminishes at temperatures above 150°C (300°F), shortening its service life.

Chemical Compatibility of NBR Seals

● Compatible Fluids for NBR

NBR seals exhibit robust chemical compatibility with various fluids, including petroleum-based hydrocarbons, vegetable oils, and some hydraulic fluids like HFA, HFB, and HFC. Their resilience to dilute acids, alkali, and salt solutions further enhances their versatility across different applications.

● Incompatible Fluids and Their Effects

However, NBR seals are not compatible with all fluids. Highly aromatic hydrocarbons, ketones, acetic acid, and other polar solvents can cause swelling or chemical attack, leading to seal degradation. Strong acids and glycol-based brake fluids also fall into the category of incompatible fluids, which can compromise the integrity and functionality of NBR seals.

Comparing NBR with Other Seals: FKM Overview

● Properties of Fluorocarbon Rubber (FKM)

Fluorocarbon Rubber (FKM), commonly known by its DuPont trade name Viton®, is another widely used material in hydraulic seals. FKM offers superior performance over a broader temperature range of -40°C to 200°C (-40°F to 400°F) and exhibits excellent resistance to a wider array of chemicals compared to NBR. This makes FKM a go-to material for more demanding applications.

● Differences Between NBR and FKM Seals

While NBR and FKM have overlapping applications, FKM seals are generally preferred in environments requiring higher temperature and chemical resistance. Type A FKM is more common and cost-effective, whereas Type G FKM offers better compatibility and resistance to weathering and ozone. Despite FKM's superior properties, its higher cost limits its use to applications where its advantages outweigh the expense.

Temperature Range and Performance

● Operating Temperatures for NBR and FKM

Temperature is a critical factor in selecting hydraulic seals. NBR seals are effective up to 120°C (250°F) but can operate at temperatures as high as 150°C (300°F) with reduced service life. Conversely, FKM seals can withstand temperatures up to 200°C (400°F), making them suitable for high-temperature applications. At low temperatures, both materials maintain functional performance, although NBR has a slight edge down to -50°C (-60°F).

● Impact of Temperature on Seal Life

The operating temperature significantly impacts the life of hydraulic seals. Elevated temperatures accelerate fluid degradation and material wear, leading to premature seal failure. NBR's performance declines faster at high temperatures, whereas FKM maintains its properties over a wider temperature range, offering longer service life in extreme conditions.

Choosing the Right Seal Material

● Factors to Consider When Selecting Seal Materials

Selecting the right seal material involves evaluating several factors, including operating temperatures, fluid compatibility, mechanical loads, and environmental conditions. The choice between NBR and FKM depends on these criteria, with NBR being suitable for cost-sensitive applications and FKM for high-performance requirements.

● Importance of Consulting Manufacturers

Given the complex nature of hydraulic systems, consulting with manufacturers is crucial when selecting seal materials. Manufacturers can provide insights into the best material choices based on specific application needs and can offer guidance on potential impacts of changing hydraulic fluids on existing seals. This collaboration ensures optimal performance and longevity of hydraulic seals.

Seals in Specialized Applications

● Usage of Thermoplastic Polyurethanes (TPU)

In specialized applications, thermoplastic polyurethanes (TPU) are often preferred. TPU seals are known for their high resilience and excellent wear resistance, making them suitable for challenging environments. They are commonly used with bio-hydraulic fluids that require robust chemical compatibility and performance.

● Applications Requiring Specialized Seal Materials

Specialized seal materials like TPU are essential in applications where standard NBR or FKM seals may not perform adequately. These include sectors like food processing, where seals must resist various chemicals, and in aerospace, where high performance under extreme conditions is necessary. Selecting the appropriate specialized seal material ensures reliability and efficiency.

Predicting and Testing Seal Compatibility

● Methods for Predicting Seal and Fluid Compatibility

Accurately predicting the compatibility of seal materials with hydraulic fluids is vital. One effective method is comparing the aniline point of the fluid with standard ASTM International reference oils. This comparison offers a useful indication of the compatibility.

● Importance of the Elastomer Compatibility Index (ECI)

The Elastomer Compatibility Index (ECI) is another valuable tool. By comparing the behavior of standard NBR compounds in various oils, the ECI helps predict how different nitrile compounds will perform. This method is particularly beneficial for determining the swelling behavior (SB) of the seal material, enabling more accurate predictions of physical interactions between the fluid and the seal.


The choice of hydraulic seals significantly impacts the performance and longevity of hydraulic systems. Acrylonitrile Butadiene Rubber (NBR) remains the most common seal material due to its cost-effectiveness and compatibility with various fluids. However, more demanding applications may necessitate the use of Fluorocarbon Rubber (FKM) or specialized materials like Thermoplastic Polyurethanes (TPU). Consulting with manufacturers and utilizing predictive methods like the Elastomer Compatibility Index (ECI) ensure optimal seal selection and system performance.

For high-quality hydraulic piston seal kits, particularly in specialized applications, it is advisable to consult leading suppliers and manufacturers who can offer tailored solutions that meet specific operational requirements. The right choice of hydraulic piston seal kits, whether sourced from a China hydraulic piston seal kit manufacturer or another reliable hydraulic piston seal kit supplier, ensures the durability and efficiency of hydraulic systems.

About Borise

Hangzhou Ruiwei Machinery Equipment Co., Ltd, under the brand name Borise, is a leading supplier of high-quality sealing systems for construction machinery. Utilizing advanced German technology, Borise specializes in producing durable polyurethane oil seals and high-resilience step seals. Known for their commitment to quality, Borise serves as a trusted hydraulic piston seal kit manufacturer and supplier to top hydraulic breaker brands in China and beyond, ensuring superior performance and reliability in demanding applications.What is the most common seal used in hydraulics?
Post time: 2024-07-06 15:00:11
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