5 Key Differences Between Static and Dynamic Seals
The type of O-ring used in a given application depends on the nature of the surfaces it contacts. The surfaces can be dynamic, which means they are in motion, or static, which means they remain stationary. If there is no motion between the mating surfaces, a static seal should be used; conversely, if there is motion between the two mating surfaces, a dynamic seal is used.
Beyond the basic distinction between the two types of seals, other key differences affect the design of the seal. The following details the unique features of these seals.
difference
1. Material selection:
Static seals: Because they are in a stationary environment, lower-hardness materials can be used for low-pressure sealing. For example, materials with lower wear resistance, such as silicone, can be used to meet the needs of a wider temperature range.
Dynamic seals: Due to the need for continuous movement, dynamic seals must be made of materials with high wear resistance and strength. High wear resistance and low friction materials such as hydrogenated nitrile compounds (such as FKM rubber or self-lubricating materials) are ideal. Generally, the higher the hardness, the lower the friction.
2. Maintenance requirements:
Static seals: When installed in a stationary environment, they tend to have a longer service life as long as the appropriate chemical and high-temperature resistant materials are selected.
Dynamic seals: Because they are affected by movement and friction, their service life is relatively short, and more frequent maintenance is required to avoid premature failure.
3. Gland design:
Static seals: Their cross-section is generally compressed by 10% to 40%. Due to the lack of movement, higher compression levels can be tolerated.
Dynamic seals: Gland design is critical to prevent premature wear. The material of the gland should not wear the O-ring during movement, and the surface finish must be compatible with it to prevent tearing and failure. The cross-sectional compression of dynamic seals is usually from 10% to only 30%.
4. Tolerance of deviation:
Static seals: Since there is no continuous movement, there is usually a higher tolerance for misalignment between the mating surfaces. Static seals can adapt to slight alignment deviations without significantly affecting their sealing effect.
Dynamic seals: Misalignment has a more obvious effect on dynamic seals because they are in a state of continuous movement. In dynamic applications, tight tolerances are often critical to prevent wear, friction, and potential seal failure.
5. Heat generation:
Static seals: In applications where heat generation is minimal or intermittent, static seals may be more suitable. Since there is no continuous movement, less heat is generated during operation.
Dynamic seals: Friction between mating surfaces caused by continuous movement can cause heat accumulation. Therefore, the design of dynamic seals must be able to dissipate heat effectively to prevent overheating, which can affect the performance of the sealing material and the performance of the overall system.
Case Showcase
Here are some real-life examples of static seals and dynamic seals:
Examples of static seals:
1. Sealing of pipe connections: In piping systems, static seals, such as gaskets, are usually used at flange connections to ensure sealing between pipes and prevent liquid or gas leakage.
2. Sealing of pressure vessels: Static seals are usually used to seal between the end caps and the barrel of pressure vessels to ensure that the pressure inside the vessel does not leak.
3. Sealing between engine block and cylinder head: Static seals, such as cylinder gaskets, are required between the cylinder block and cylinder head of automobile engines to prevent leakage of engine oil and coolant.
Examples of dynamic seals:
1. Sealing of hydraulic cylinders: Dynamic seals, such as sealing rings, are required between the piston and the barrel in the hydraulic cylinder to prevent leakage of hydraulic oil and ensure smooth movement of the piston.
2. Sealing of rotating shafts: In various mechanical equipment, dynamic seals, such as oil seals, are usually used between rotating shafts and bearing seats to prevent leakage of lubricating oil and entry of external impurities.
3. Pump seal: Dynamic seals are required between the impeller shaft and the pump housing to ensure the normal operation of the pump and prevent liquid leakage.
4. Valve seal: Dynamic seals are usually used to seal between the valve stem and the valve body to ensure that there is no leakage when the valve is switched on and off.
Dynamic seals and static seals have their characteristics, and they play a vital role in ensuring the normal operation and safety of equipment.
