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Static and Dynamic o rings

Static and Dynamic o ringsA range of factors and application dynamics come into play when choosing a particular type of o ring. 

You need to understand the type of seal exert you require, the dimensions, and even compounds. 

Due to the nature of an o ring and its overall design, o rings use both radial and axial stress to exert a seal. 

O rings can exert static and dynamic sealing actions, and it’s important to understand the difference between the two o ring types so you can choose the best fit for your application. 

Difference between static and dynamic seals 

We typically use static seals when there is no relative motion between the mating surfaces, i.e., a seal placed between two stable components. 

Therefore, dynamic seals are the opposite, i.e.; they are used when moving between the two surfaces is apparent. Required to prevent leakage, dynamic seals help contain pressure, creating a barrier between moving and stationary surfaces. Mainly found in applications such as cylinders, motors, pumps, pistons, etc.

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Static and dynamic o rings 

Static seals 

For static seal applications, o rings are compressed inside the seating, flattening the o ring to the two surfaces, ensuring a tight seal. However, the percentage of flattening that takes place is important to guarantee high performance. 

In essence, the better the material’s elasticity, the greater the flattening percentage needs to be to guarantee high quality and top-performing seals. 

In static seals, pressure and temperature fluctuations will affect an o-rings movement between the surfaces, so you must look out for wear and tear and potentially any superficial damage. 

Dynamic seals 

In a dynamic seal application, o rings can face various problems because of the level of friction due to the rubbing along the seal surfaces (this often causes extrusion caused by excessive friction on the sliding surfaces). This, as well as rising temperatures all, compromise the seal and its overall effectiveness. 

It is possible to limit the friction by circulating fluid around the application, acting as a lubricant, and decreasing wear. 

Note: An increase in temperature and a reaction to contact can cause an increment in the o ring volume, which can lead to deterioration of the overall component and loss of sealability. 

Stress factors: 

Radial seal stress – forces acting on the o ring level with preloading deformation help to guarantee the seal is exerted. 

Axial seal stress – forces in this instance act perpendicular to the level of the o ring for the preloading deformation to guarantee the seal is exerted. 

There are three different types of sealing effect that can take place when we consider the assembly and positioning of the o ring in any given situation. 

For example: 

Flange seal – two parallel surfaces compress the o ring, which is then subjected to preloading deformation of an axial type. 

Cylinder seal – here, the o ring is deformed with radial type preloading as the o ring is inserted suitably on the female element of the assembly. 

Piston seal – the o ring is inserted in the shaft of the assembly with the preloading deformation for the seal constituting a radial type. 

These three seals can be used in static and dynamic situations, stressing the o rings in different ways.  This makes it vital for designers and product manufacturers to choose an o ring that best suits their specific operating system. 

Influences on sealing capacity 

  • Surface finish 
  • Contact with the elastomer 
  • Operating temperature 
  • Pressure exertion 
  • Type of fluid in containment. 

These influences will affect seal performance, and using the wrong type of o ring can have negative implications for the overall product or application. 

At Specialist Sealing Products, we stock a range of o rings, gaskets, and seals comprising different materials and types, ensuring we have something suitable for all applications and specifications. 

If you have any queries or would be interested in further information on static and dynamic o rings, please call our team today; we’d be happy to help.

Read the next blog: Keeping your o ring bonded

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