O-ring seals (OR) are the most well-known and versatile type of seals.
They are suitable for installation in both static (static sealing) and moving machine parts (dynamic sealing).
They are notable for their ease of installation and the wide range of materials available for various operating conditions.
With the advancement of automation, the use of O-rings has expanded into areas such as:
- Mechanical engineering
- Pneumatics
- Hydraulics
- Installations
By incorporating additional support rings, their application has extended to high-pressure media sealing. Support rings are typically made of PTFE (Teflon), which features a low coefficient of friction and excellent chemical and thermal stability.
Support rings prevent the seal from being pushed out of the groove into the space (gap) between the sealed surfaces, thereby extending the seal's lifespan. The use of support rings is justified in the following cases:
- At higher pressures
- At larger gaps between the sealed surfaces
- With higher relative speeds of the sealed surfaces
- At higher operating temperatures, e.g., temperature fluctuations
- In dirty systems
The area of O-ring seals is covered by various standards.
The German standard, DIN 3770, which aligns with the international standard ISO 3601, is the most common in our region (tolerance, quality criteria).
Use according to the type of sealing:
Static sealing
a.) O-rings are used as flanges, covers, and couplings in installation seals…
Dynamic sealing
a.) Sealing elements with translational motion (unilateral/bilateral sealing) in components belonging to hydraulic and pneumatic systems (cylinders, rods, distribution slides, etc.).
b.) Sealing elements with rotational motion (shafts, bearings, gears, etc.).
The advantages of using O-rings compared to other seals are:
- Easy installation
- Wide application (static, dynamic, unilateral, bilateral operation)
- Wide selection of sizes and materials
- Symmetrical cross-section that prevents incorrect installation
- Simple groove shapes (space and cost savings during production)
- Low cost
For proper O-ring selection, the following must be known:
- Pressure (hardness selection – shA / support rings?)
- Operating conditions, temperature, medium (material selection)
- Groove dimensions, i.e., piston and cylinder sizes (installation dimensions)
- Type of sealing (static / dynamic – translational, rotational)
When selecting an O-ring, sufficient tolerance for the inner diameter "d" should be considered with the correct thickness "s," which does not affect sealing quality:
- Up to 5% smaller "d" (external sealing)
- Up to 3% larger "d" (internal sealing)
Operating Conditions:
O-rings are self-contained sealing elements with dual functionality. The thread forces created during installation (pre-tension of the diameter) are further increased by the system's media pressure. This generates an overall pressure (contact with surfaces in all directions), which increases as the system pressure rises.
Marking of O-rings (DIHTA):
- O-rings are dimensionally marked with the inner diameter "d" and cross-sectional thickness "s" (e.g., OR 100 x 3 // d = 100 mm; s = 3 mm)
- OR _d x s _N xxx
- Material markings – type of elastomer
- Seal cross-sectional thickness (mm)
- Inner diameter of the seal (mm)
- Group markings
The selected material is crucial for the sealing ability, operational reliability, and lifespan of the seal.
The right material – one that is tailored to the operating conditions – and the shape of the seal are decisive for the flawless operation of the seal.
Temperature, pressure, and the type of medium are key factors in selecting the proper material.
