Axial Seals vs Radial Seals: What Is the Difference

Axial seals and radial seals are two crucial components in various industrial applications. This comprehensive article explores the differences between these seal types, their functionalities, and the key factors to consider when choosing the appropriate seal for your specific needs.

What Are Axial Seals

Axial seals, also known as face seals or thrust seals, are designed to prevent leakage along the axis of a shaft or bore. These seals are typically used in applications where the primary motion is perpendicular to the seal face, such as in plug-type applications or where axial clamping is required.

How Compression Is Applied

In axial seals, compression is applied to the top and bottom surfaces of the seal’s cross-section. This compression creates a tight seal between the mating surfaces, preventing fluid or gas from escaping.

What Are Axial Seals Used For

• Plug-type applications: Axial seals are commonly used in valves and similar devices, where they prevent leakage around the plug or stem.
• Crush seal applications: Axial seals are compressed between two surfaces to create a static seal, often used in high-pressure or high-temperature environments.
• Thermal expansion applications: These seals can accommodate thermal expansion and contraction in systems where temperature fluctuations are expected, maintaining a proper seal throughout the operating range.

What Are Radial Seals

Radial seals, also referred to as shaft seals or bore seals, are designed to prevent leakage around the circumference of a shaft or bore. These seals are used in applications where the primary motion is parallel to the seal surface, such as in rotating shafts or reciprocating rods.

How Compression Is Applied

In radial seals, compression is applied to the outside and inside diameters of the seal. This compression creates a tight fit between the seal and the mating surfaces, preventing fluid or gas from escaping.

Types of Radial Seals

Radial seals can be categorized into two main types: dynamic radial seals and static radial seals.

Dynamic Radial Seals

Dynamic radial seals are used in applications where there is relative motion between the seal and the mating surface. Examples of dynamic radial seals include:

1. Radial shaft seals: These seals are used to prevent leakage around rotating shafts, such as in pumps, motors, and gearboxes.
2. Radial lip seals: Radial lip seals feature a flexible lip that maintains contact with the rotating shaft, providing an effective seal.
3. Track pin seals: These seals are used in heavy-duty applications, such as construction machines, to seal pivot points and prevent contamination.

Static Radial Seals

Static radial seals are used in applications where there is no relative motion between the seal and the mating surface. Examples of static radial seals include:

1. O-rings: O-rings are versatile seals that can be used in a variety of static sealing applications, such as in hydraulic cylinders and pipe fittings.
2. Square and rectangular seals: These seals are used in applications where a simple, cost-effective static seal is required, such as in machine tools and industrial machinery.

What Are Radial Seals Used For

Radial seals are used in a wide range of applications, including:

• Rotating shafts: Radial seals are commonly used to prevent leakage around rotating shafts in equipment such as pumps, motors, and gearboxes.
• Reciprocating rods: In hydraulic and pneumatic cylinders, radial seals are used to seal reciprocating rods, preventing fluid or gas from escaping.
• Bore sealing: Radial seals can be used to seal bores in various components, such as valve bodies, manifolds, and housings.

Key Factors When Choosing between Axial and Radial Seals

Gland Design and Dimensions

Axial seals require a specific gland design that allows for proper compression and retention, while radial seals need a gland that provides adequate support and maintains the desired seal geometry.

Type of Motion (If Any)

Axial seals are best suited for applications with little to no relative motion between the seal and the mating surface, while radial seals are designed to accommodate rotary or reciprocating motion.

Operating Pressures

Axial seals are typically used in high-pressure applications, as they can withstand significant axial forces. Radial seals, on the other hand, are suited for a wide range of pressures, depending on the specific seal design and material.

Gaps and Tolerances

Axial seals generally require tighter tolerances to ensure proper compression and sealing, while radial seals can accommodate larger gaps and tolerances due to their flexible nature.

Surface Finishes

Axial seals typically require smoother surface finishes to maintain an effective seal, while radial seals can tolerate slightly rougher surfaces due to their conformability.

Presence of Contaminants

The presence of contaminants in the system, such as dirt, dust, or abrasive particles, can affect seal performance. Radial seals, particularly those with auxiliary dirt seals or exclusionary features, can provide better protection against contaminants compared to axial seals.

Conclusion

Understanding the differences between axial seals and radial seals is essential for engineers and designers to select the appropriate sealing solution for their specific applications. By considering factors such as gland design, type of motion, operating pressures, gaps and tolerances, surface finishes, contaminants, and material properties, one can ensure optimal seal performance and reliability in their systems.