Each O-ring serves a different purpose, so when selecting one, we need to think about its working environment, sealing requirements, physical properties, and more. It's like choosing the right outfit for ourselves in life—some O-rings are suitable for machinery, some for the automotive industry, and others for electronic products. We must consider various physical properties of O-rings to meet our customers' genuine needs. So, when selecting O-rings, what specific factors should we consider?

1) Working Media and Conditions
When choosing the material for O-rings, we first consider its compatibility with the working media. Then, we take into account factors such as pressure, temperature, continuous working time, operating cycles, and more. If used in rotating applications, we need to consider the temperature rise caused by frictional heat. Different sealing materials have varying physical and chemical properties.

2) Sealing Form
Based on load type, we can categorize them into static and dynamic seals. Based on sealing purposes, we have hole seals, shaft seals, and rotary shaft seals. Installation forms can be radial or axial. For radial installation and shaft seals, we aim to minimize the deviation between the O-ring inner diameter and the sealed diameter. For hole seals, the inner diameter should match or be slightly smaller than the groove diameter. When axially installed, we consider the direction of pressure. For internal pressure, the O-ring's outer diameter should be about 1% to 2% larger than the groove's outer diameter; for external pressure, the O-ring's inner diameter should be about 1% to 3% smaller than the groove's inner diameter.

3) Other Factors Affecting Sealing Performance

① O-ring Hardness: The hardness of O-ring material is a crucial indicator of sealing performance. It determines the compression and maximum allowable extrusion gap of the O-ring.

② Extrusion Gap: The maximum allowable extrusion gap is related to system pressure, O-ring cross-sectional diameter, and material hardness. Generally, the higher the working pressure, the smaller the maximum allowable extrusion gap. Exceeding this gap range can lead to O-ring extrusion or damage.

③ Compression Set: Another indicator of O-ring sealing performance is the compression set of the selected material. Under pressure, the O-ring, as an elastic element, undergoes elastic deformation, which can lead to permanent plastic deformation with increasing pressure. To prevent permanent plastic deformation, the maximum allowable compression for O-rings is around 30% in static seals and 20% in dynamic seals.

④ Pre-compression Amount: When installing O-rings in grooves, an initial compression amount should be reserved to ensure their sealing performance. The pre-compression amount varies relative to the cross-sectional diameter W for different applications. Typically, it's around 15% to 30% in static seals and 9% to 25% in dynamic seals.

⑤ Stretching and Compression: When installing O-rings in grooves, they experience stretching or compression. Excessive stretching or compression can cause the O-ring's cross-section to increase or decrease significantly. Stretching by 1% reduces the cross-sectional diameter by about 0.5%. For hole seals, it's best for the O-ring to be in a stretched state, with a maximum allowable stretch of 6%; for shaft seals, the O-ring is ideally compressed along its circumference, with a maximum allowable circumference compression of 3%.

When unsure of how to choose the right O-ring, we can consider factors such as working media, working conditions, sealing form, and more to avoid many pitfalls.

At HAISUN Rubber, we customize O-rings based on the specific performance requirements of our customers, with our professional engineers ready to provide expert guidance.