The difference between dynamic and static seals in hydraulic systems: types, selection, application, structural design, etc. Seals are categorized as dynamic seals and static seals.
Specific types of seals:
Dynamic seals can be divided into contact and non-contact seals based on the type of contact between the sealing surfaces. Contact seals are predominant in hydraulic cylinders. Dynamic seals involve relative motion between the sealing surface and the cylinder body. These motions are generally categorized into the following main types: reciprocating (linear), rotational, oscillating, and spiral.
Static seals involve no relative motion between the sealing surface and the cylinder body components. They can be categorized as flat static seals (axial), cylindrical static seals (radial), and angular static seals. Their leakage gaps are axial and radial, respectively.
About the classification of seals in hydraulic cylinders:
Reciprocating:
Seals between the cylinder body and the piston bore (also known as outer diameter seals or piston seals) include guide rings and piston seals.
Seals between the piston rod and the sealing end cap (also known as inner diameter seals or piston rod seals) include guide rings, buffer seals, piston rod seals, and dust seals.
Static seals:
The connection between the cylinder barrel and the end cap (cylinder head/bottom), the fixed connection between the piston and the piston rod,
the fixed surface of the dust seal gland
Differences in the seal ring structures of dynamic and static seals:
1. Dynamic seals are more complex than static seals. Some dynamic seals can also be used to achieve static sealing. They often use elastomers in designs such as lip seals (such as U-, V-, Y-, and L-rings) or spring-loaded lip seals. Other seals include extruded seals made of high-hardness materials (PTFE) and rubber, such as Glyd rings, Step seals, and T-seals. These seals utilize fluid pressure to tighten (self-sealing).
2. The most commonly used static seal is the O-ring. Different elastomer materials are used depending on the operating conditions. They are often used with retaining rings. Dynamic seals with static sealing functions can also be used as an alternative, such as dumbbell seals, lap seals, and T-seals. Depending on the operating conditions, more wear-resistant and extrusion-resistant materials, as well as designs that are more cost-effective and have a longer service life, can be selected.
3. Regarding the use of O-rings in dynamic and static sealing, O-rings can be used for dynamic seals in applications where sealing requirements are less stringent. However, in dynamic and static sealing applications with the same groove dimensions, the required O-ring inner diameter and wire diameter are different. This is due to the interference fit design. Typically, the interference fit for dynamic seals is lower than that for static seals. While there are many specific numerical standards in the industry, the ranges vary between manufacturers. To achieve optimal sealing performance and service life, the actual choice should be made based on a comprehensive consideration of the entire sealing system.
Other Key Differences:
Core Focus: The core challenge of dynamic seals is to overcome friction and wear caused by movement; the core challenge of static seals is to resist permanent deformation and stress relaxation caused by long-term compression.
Material Property Focus: Dynamic seal materials emphasize wear resistance, low friction, and thermal conductivity; static seal materials emphasize high elastic recovery and resistance to compression set.
Installation Precision: Dynamic seal installation generally requires higher precision and surface quality. Turning processes can more reliably ensure dimensional accuracy, avoid dimensional fluctuations caused by molds, and ensure more stable sealing performance.
Dynamic seal selection factors include friction, wear, heat generation, and lubrication. They must maintain a tight seal during movement while minimizing friction and wear.
Static seal selection factors include pressure/temperature resistance, surface defect compensation, extrusion resistance, and permanent deformation resistance. They must maintain elastic recovery even under long-term static conditions.
Common selection factors for both dynamic and static seals include compatibility with the media, material hydrolysis (aging) resistance, interference design, structural design, temperature, and cylinder surface roughness.
P.S.: For hydrolysis-resistant polyurethane, we recommend our HPU, a polyether-based MDI material. It offers excellent hydrolysis resistance, superior physical properties, low wear, and low compression set. Please contact us for a detailed TÜV Rheinland material test report.
Understanding these differences is crucial for the correct selection, installation, and maintenance of seals, effectively preventing equipment leaks and ensuring reliable system operation. Qingdao Klock Seals has been specializing in turning seals for over a decade and specializes in turning seals. We are particularly adept at designing and developing customized sealing system solutions, providing professional sealing solutions. We have a stock of semi-finished barrels of sealing rings in various sizes from 0-4000mm, which supports rapid proofing. If you have any sealing-related questions, please feel free to contact us.
