Sealing Principle Of O-ring Seal

The O-ring seal has a wide application range. If the material is selected properly, it can meet the requirements of various motion conditions. The working pressure can be from 1.333×105Pa vacuum to 400MPa high pressure; the temperature range can be from -60°C to 200°C.


Compared with other sealing types, the O-ring seal has the following characteristics:


1)Small structure size, easy assembly and disassembly.


2) Both static and dynamic seals can be used, and there is almost no leakage when used as a static seal.


3) A single O-shaped sealing ring is used to have a two-way sealing effect.


4) The dynamic friction resistance is small.


5) Low price.


O-ring seal is a kind of squeeze type seal. The basic working principle of squeeze type seal is to rely on the elastic deformation of the seal to cause contact pressure on the sealing contact surface. If the contact pressure is greater than the internal pressure of the sealed medium, it will not occur. Leakage, and vice versa, leakage occurs. When used for static seal and dynamic seal, the causes and calculation methods of the contact pressure of the seal contact surface are different, and they need to be explained separately.


1. The sealing principle when used for static sealing


O-rings are the most widely used in static sealing. If the design and use are correct, the O-ring seal can achieve a leak-free seal in the static seal.


After the O-ring is installed in the sealing groove, its cross-section is subjected to contact compression stress and elastically deforms. A certain initial contact pressure Po is generated on the contact surface. Even if there is no medium pressure or the pressure is very small, the O-ring seal can be sealed by its own elastic force; when the cavity is filled with a pressurized medium, the O-ring seal will be displaced under the action of the medium pressure , Move to the low pressure side, at the same time its elastic deformation is further increased, filling and closing the gap


In theory, even if the compression deformation is zero, it can be sealed under oil pressure, but in fact, the O-ring may be eccentric when installed. Therefore, after the O-ring is installed in the sealing groove, its cross-section is generally compressed and deformed by 7% to 30%. The static seal takes the larger compression rate value, and the dynamic seal takes the smaller compression rate value. This is because synthetic rubber needs to be compressed at low temperatures, so the pre-compression of static seal O-rings should be considered to compensate for its low-temperature shrinkage.


2. The sealing principle when used for reciprocating sealing


In hydraulic rotating, pneumatic components and systems, reciprocating sealing is one of the most common sealing requirements. Reciprocating seals are used on power cylinder pistons and cylinder blocks, piston intervention cylinder heads, and various slide valves. The gap is formed by a cylindrical rod and a cylindrical hole, and the rod moves axially in the cylindrical hole. The sealing effect limits the axial leakage of the fluid. When used as a reciprocating seal, the pre-sealing effect and self-sealing effect of the O-ring are the same as static sealing, and due to the elastic force of the O-ring itself, it has the ability to automatically compensate after wear. However, when the liquid medium is sealed, the situation is more complicated than static sealing due to the rod movement speed, liquid pressure, and viscosity.


O-rings are used as reciprocating seals with compact structure and small size, which can reduce component prices. Mainly used in:


1) Low-pressure hydraulic components are generally limited to short strokes and medium pressures of about 10MPa.


2) In hydraulic spool valves with small diameter, short stroke and medium pressure.


3) Pneumatic slide valve and pneumatic cylinder.


4) As an elastic body in a combined reciprocating sealing device.


3. Seal for rotary motion


In rotary motion seals, oil seals and mechanical seals are usually used. However, the operating pressure of the oil seal is relatively low, and compared with the O-ring, it is too large and complicated, and the manufacturability is also poor. Although mechanical seals can be used for high pressure (40MPa), high speed (50m/s) and high temperature (400°C), their structure is more complex, large, and costly. They are only suitable for some heavy machinery and equipment for petroleum and chemical industries.


O-ring seals are being widely used in rotary motion sealing devices due to their small size, simple structure, low cost, good process performance, and wide application range.