O-rings are often used in industry and daily necessities. Although they are not expensive, they have a decisive impact on the regular use of equipment. O-rings are the most widely used seals in hydraulics and pneumatics, but Improper selection, groove design, processing and assembly often cause oil leakage. Therefore, before choosing a seal ring, you must clarify the application scenario. Whether it is a dynamic pressure seal or a static pressure seal, whether it is an internal pressure or an external pressure, it is only reasonable. The correct choice of seal ring depends on the application scenario. Choosing the correct O-ring for your application is critical to ensuring good sealing and high performance.
This article will help you recognize and select some of the critical factors to consider when choosing the best O-ring for your needs.
Material
The first thing to consider is your choice of material. Understand the compatibility of the O-ring material with the application environment, what type of chemical substances it is resistant to, and whether the material will also affect the compression amount of the O-ring and whether it can withstand the high and low temperatures of the working environment. Able to withstand pressure conditions, friction resistance, etc. Different materials have varying degrees of resistance to chemicals, temperature extremes and other factors. It is critical to evaluate the compatibility of O-ring materials with the fluids, gases, and environmental conditions to which they will be exposed. It will help prevent premature O-ring failure or degradation, thereby reducing downtime and improving economic efficiency. If you need to know the characteristics of O-rings made of different materials, you can click on O-ring materials to introduce the material knowledge points specifically.
Dimensions
O-rings should be sized to match the groove or equipment in which they are installed. The O-ring should fit snugly in the groove without excessive stretching or compression. Improper sizing may result in leaks or poor sealing. O-ring dimensions are expressed by outer diameter, inner diameter, and wire diameter. On our engineering drawings, we only need to indicate the dimensions of the inner diameter and wire diameter or the dimensions of the outer diameter and wire diameter. The outer diameter is equal to 2*wire diameter+inner diameter. You can choose one of these two to calculate. The old national standard adopts the marking method of “outer diameter × wire diameter”, and the new national standard adopts the marking method of “inner diameter × wire diameter”. According to the shaft diameter, the inner diameter of the O-ring of the corresponding size can be selected. Generally speaking, you can choose a shaft that is smaller than the inner diameter so that it can be installed tightly and will not fall off easily. The hole should be giant so that it is not easily squeezed.
Temperature
Understand the operating temperature range of O-rings. Different materials can withstand different temperatures. Some materials are resistant to high temperatures but may become brittle or lose elasticity at low temperatures; some materials are resistant to low temperatures but may melt or be damaged under high-temperature conditions. , so it is essential to select an O-ring material that can withstand the expected temperature range of the application.
Pressure
The pressure rating of an O-ring, the difference between internal pressure and external pressure, is also an important consideration. O-rings need to withstand the pressure exerted on them without deforming or failing. It is critical to select an O-ring with the appropriate pressure rating to ensure a reliable seal under expected operating conditions.
Internal pressure： refers to the pressure exerted on the inner diameter of the O-ring. In applications where the fluid or gas being sealed is under pressure, the O-ring can withstand pressure from the inside, which pushes the O-ring toward the gland wall to enhance the sealing effect.
The main factors to consider for internal pressure include:
Squeeze effect: The “squeeze effect” is caused by internal pressure, causing the O-ring to deform slightly. The standard material for O-rings (usually an elastomer such as nitrile rubber or fluoroelastomer) compresses against the gland wall, forming a tight seal. The elasticity of the O-ring material allows it to maintain a seal under varying internal pressures.
Deformation and extrusion: Under high internal pressure, O-rings can become deformed and extruded. When an O-ring is compressed beyond its elastic limit, it will bend, possibly resulting in reduced sealing performance. Extrusion, on the other hand, is the process by which O-ring material is forced into gaps or gaps within the gland, compromising sealing performance.
External pressure ：refers to the force exerted on the outer diameter of the O-ring. This pressure comes from the external environment or the system’s O-ring. External pressure will affect the sealing effect and durability of the O-ring.
Balance internal pressure: External pressure helps balance the interior pressure acting on the O-ring. By applying pressure to the outer diameter, the external pressure assists in resisting the squeezing effect caused by internal pressure, thereby improving overall sealing performance.
Support and restraint: External pressure provides support and restraint to the O-ring, helping it maintain its shape and position within the gland. This support prevents the O-ring from shifting or extruding into gaps, ensuring a consistent and effective seal.
Under external pressure: The inner diameter of the O-ring is the same as the inner diameter of the groove. It is necessary to prevent the O-ring diameter from becoming smaller under working pressure;
Under internal pressure: the outer diameter of the O-ring is the same as the outer diameter of the groove.
O-rings are subject to tension or compression when installed inside the groove. Suppose the values of tension and compression are too large. In that case, it will cause the cross-section of the O-ring to increase or decrease excessively because stretching 1% will correspondingly reduce the cross-section diameter by about 0.5%. For hole (internal pressure) sealing, the O-ring is best in a stretched state, and the maximum allowable stretch is 6%; for shaft (internal pressure) sealing, the O-ring is best compressed along its circumferential direction. The maximum permissible girth compression is 3%. The maximum allowable extrusion gmax of the O-ring is related to the system pressure, the O-ring cross-sectional diameter and the material hardness. Generally, the higher the working pressure, the smaller the value of the maximum allowable extrusion gap gmax. If the gap gmax exceeds the permissible range, it will cause the O-ring to be extruded or even damaged. When the pressure exceeds 5MPa, it is recommended to use a back-up ring.
O-ring groove design
The groove volume is about 15% larger than the O-ring volume. Design parameters: shape, size, accuracy, roughness. For dynamic seals, relative motion clearance needs to be calculated. The principle is easy to process, reasonable in size, easy to ensure accuracy, and easy to disassemble and assemble. Different designs have different sealing properties.
O-ring groove depth design: The design of the groove depth determines the design compression amount of the O-ring. The groove depth plus the gap is less than the wire diameter of the O-ring in its free state. The compression amount of the O-ring is composed of the inner diameter compression amount δ’ and the outer diameter compression amount δ”.
O-ring groove notch and groove bottom fillet design:
Notch rounded corners: Prevent cuts and scratches during O-ring assembly. R=0.1~0.2mm. If it is too large, extrusion will occur, and if it is too tiny, cuts will occur.
Fillet at the bottom of the groove: to prevent stress concentration, dynamic seal: R=0.1~1mm, static seal: R=d0/2mm
O-ring groove surface roughness design: static seal: Ra=6.3~3.2; dynamic seal: Ra=1.6; rotary seal: shaft groove: Ra=0.4 or less.
Application requirements
You also need to consider the specific requirements of your application when selecting an O-ring. Factors such as the frequency of assembly and disassembly, the need for lubrication, and the presence of abrasive particles. For example, in dynamic applications, O-rings with low friction and wear resistance may be a better choice.
Quality and certification
To ensure that the O-rings you choose are of high quality and meet industry standards, look for them to come from reputable O-rings manufacturers who follow strict quality control processes. Additionally, check whether the O-ring has relevant certifications, such as ISO9001, to ensure its reliability and performance.
Production and supply capabilities
In order to respond to market demand and reduce downtime, as a middleman, you need to choose a company with solid production and supply capabilities to meet timely delivery requirements.
After-sales service and technical support
When choosing a good quality O-ring manufacturer, you also need to consider the manufacturer’s customer service capabilities and the manufacturer’s professional technical support to help you solve any customer and technical problems in a timely manner.
Price
Choose a reasonable price and high-cost performance. Although price is important, considering the critical impact of seals on equipment, you still need to assess product quality and performance and not sacrifice quality in exchange for a low price to ensure the equipment’s reliability. Normal use and customer satisfaction better solve the needs of your users.
By carefully evaluating these factors, you can select the correct O-ring for your equipment to provide an effective seal and ensure optimal performance in your specific application. This article is for your reference only. If you need to find a hydraulic sealing solution for your special working conditions, please get in touch with the TYS expert team to help you analyze.
