The O-ring is a circular rubber ring, which is the most used seal in hydraulic and pneumatic systems. O-rings can have circular, square, X-shaped and Y-shaped cross-sections, each shape having different properties and applicability.
1. The sealing principle of O-rings
The O-ring is a two-way sealing element. When installed, the initial compression of the O-ring in the radial or axial direction determines its initial sealing ability. The force generated by the system pressure acting on the O-ring is its total sealing force; this sealing force increases as system pressure increases.
Under pressure, the shape of the O-ring and the liquid with high surface tension are similar. Pressure is transmitted equally in all directions.
O-ring self-sealing is limited. When the internal pressure is too high, the O-ring “rubber extrusion” phenomenon will occur. In other words, due to the existence of a gap in the sealed part, the O-ring under high pressure will generate stress concentration in the gap.
When the tension reaches a level that the rubber material of the O-ring cannot withstand, the rubber material will be squeezed. At this time, although the O-ring can still temporarily maintain the seal, it has actually been damaged.
Therefore, it is necessary to strictly select the type.
2. Features of sealing rings
1. Advantages of sealing rings
- Simple design, compact structure, easy to install and remove;
- Suitable for various sealing forms, dynamic and static seals can be used;
- The cross-section structure of the sealing ring is extremely simple and has a self-sealing function. The sealing performance is reliable, and there is almost no leakage in the static seal;
- The resistance to friction during movement is small, making it suitable for situations with alternating pressure;
- Single-use two-way seal;
- The size and groove have been standardized, the product is readily available, easy to use and purchase, and the price is relatively low.
2. Disadvantages of O-rings
- During dynamic compression sealing, the initial frictional resistance is high;
- In the process of sealing air pressure and water pressure, it is necessary to add lubricating oil to prevent wear. In some situations, it is often necessary to add protective and dust-proof retaining rings;
- The processing dimensions and accuracy requirements of corresponding parts (such as moving surfaces, grooves, gaps, etc.) are strict.
3. Precautions for installing the O-ring
1. Basic requirements for O-ring installation
Before installing the O-ring, check the following:
- If the chamfer is processed according to the drawing, check whether the sealed surface has any defects;
- Whether the inside diameter has been deburred, whether sharp edges have been rounded, and whether all edges or transitions have been chamfered;
- Whether the processing burrs and iron filings have been completely removed, ensuring that all processing residues are eliminated;
- Whether the ends of the threads in the installation path have been covered to prevent them from scratching the O-ring;
- If seals and parts have been coated with a small amount of lubricating grease or oil compatible with the O-ring;
- Do not use lubricating grease that contains solid additives such as molybdenum disulfide and zinc sulfide.
2. For manual installation, please note the following:
- Do not use sharp tools;
- Make sure the O-ring is not twisted, use auxiliary tools to ensure correct positioning.
- Avoid overstretching the sealing rings;
- For O-rings bonded with sealant tape, do not stretch at the connection point;
- O-rings are generally not reusable;
- When installing an O-ring into a groove, be careful not to twist the O-ring.
3. When installing over threads, splines
- After stretching an O-ring, when passing through threads, splines, keys, etc., an installation mandrel must be used. This chuck can be made of metal or softer plastic and should have no burrs or sharp edges.
- When installing tightening screws, the screws must be tightened symmetrically and not in directional sequence.
