Seals are used to prevent fluids or solid particles from passing through gaps between adjacent mating surfaces. They provide a sealing effect to stop fluid leakage and also block external impurities and dust from entering the interior of mechanical equipment, which would otherwise cause rusting of the equipment’s components. So, what are the specific classifications of seals?

1.Classification by Function

Seals can be categorized into six types based on their function, and these types are commonly used in industries such as chemical engineering, national defense, and petroleum. Therefore, the selection of high-quality seals is of great importance to many enterprises:

• Shaft Seals: Designed for sealing reciprocating or rotating shaft components (e.g., piston rods, rotating shafts) to prevent internal media from leaking along the shaft.

• Bore Seals: Used to seal the inner walls of fixed bore components (e.g., cylinder blocks, valve bodies), preventing media leakage from the gap between the bore and moving parts (e.g., pistons).

• Dust Seals: Block external dust, impurities, and moisture from entering the sealed system, protecting the main seal and internal equipment components.

• Guide Rings: Provide radial guidance and support for moving parts (e.g., pistons, piston rods) to prevent uneven wear and ensure stable sealing performance.

• Static Seals: Seal stationary mating surfaces (e.g., flanges, end caps, cabinet joints) to stop media leakage from fixed gaps.

• Rotary Seals: Seal rotating components (e.g., rotating shafts, drive shafts) while maintaining dynamic sealing performance and preventing leakage.

2. Classification by Material

Additionally, seals can be classified by their material. Common materials used for seals include nitrile rubber (NBR), ethylene propylene diene monomer (EPDM) rubber, fluororubber (FPM/Viton), silicone rubber (SI), fluorosilicone rubber (FVMQ), nylon (PA), polyurethane (PU), and engineering plastics. Among these, rubber materials are the most widely used due to their stable overall performance compared to other materials.