In crane hydraulic cylinders, what are the differences in design between static seals and dynamic seals?

In crane hydraulic cylinders, there are significant differences in the design of static and dynamic seals, which are primarily reflected in the following aspects:

1. Movement State Between Sealing Surfaces
Static Seal: The sealing surfaces of static seals typically do not experience relative motion; they remain stationary. Therefore, the design of static seals focuses mainly on ensuring a tight fit between the sealing surfaces to prevent hydraulic oil leakage from the connection.

Dynamic Seal: The sealing surfaces of dynamic seals experience relative motion, such as the movement between the piston and the cylinder body, or between the piston rod and the cylinder head. The design of dynamic seals must take into account both the sealing performance and the wear, friction, and other issues caused by relative motion.

2. Selection of Sealing Materials
Static Seal: Static seals have relatively lower material requirements, mainly focusing on the material's corrosion resistance, elasticity, and compressive deformation capacity. Common materials for static seals include rubber, plastics, and metals.

Dynamic Seal: Dynamic seals have higher material requirements, needing materials with excellent wear resistance, high-temperature resistance, corrosion resistance, and good elasticity and rebound properties. Common materials for dynamic seals include polyurethane, PTFE (polytetrafluoroethylene), and rubber (such as nitrile rubber, fluororubber).

3. Sealing Structure Design
Static Seal: The structural design of static seals is relatively simple, usually achieved through sealing rings, gaskets, and other components. These components must ensure a tight fit with the sealing surface during assembly to form an effective seal.

Dynamic Seal: The structural design of dynamic seals is more complex, as it needs to consider issues such as friction and wear caused by relative motion. Therefore, dynamic seals often employ a multi-stage sealing design. For example, piston rod seals typically use combinations of Y-rings, U-rings, and other sealing forms to enhance sealing effectiveness and durability.

4. Maintenance and Replacement
Static Seal: Maintenance of static seals is relatively simple, typically requiring periodic inspection of the sealing surface wear. If necessary, sealing rings or gaskets are replaced.

Dynamic Seal: Maintenance of dynamic seals is more complex, requiring regular inspection of the sealing ring wear. Severely worn sealing rings should be replaced. Additionally, replacing dynamic seals is more difficult as it requires disassembling the relevant parts of the hydraulic cylinder and reassembling with new seals.