The function of O-RING and how to use it correctly

1. What is O-RING
O-RING is a moderately compressed O-shaped (circular) sealing ring installed in a groove. It can be used as a seal for various fluids such as oil, water, air, and gas. There are two types of usage: static and moving.
2. Correct usage of O-RING
2-1. Selection of cutting diameter
Under the condition of constant compressibility, the permanent deformation will be small if the cut-off diameter is large, and the O-ring with large cut-off diameter can obtain stable sealing performance. Especially when used as a dynamic seal, the large cut-off diameter has the effect of preventing twisting.
2-2. Use at high pressure
O-RING functions because of the compressive stress of the material. In addition, the pressure of the sealing fluid exerts the effect of safety sealing. Therefore, the pressure limit should be considered in principle. The actual use of the O-ring must generate the pressure of the sealing medium fluid to keep the O-ring from being bitten.
Therefore, the actual pressure resistance of O-RING is determined by the relationship between the mechanical strength of the material (as a representative value: hardness) and the gap.
When the retaining ring bears pressure from two directions, the retaining ring can be installed on both sides of the O-ring at the same time. When the pressure is received from one direction, a retaining ring is installed on the opposite side of the pressure. The shape of the retaining ring has three types: ring type, oblique cut type and spiral type. From the perspective of use effect, the circle shape is the best. From the perspective of easy installation, the oblique and spiral ones are the most convenient.
2-3. Use for different purposes
① Cylindrical static seal
Even if the O-ring and the groove size are used in accordance with the JIS standard, due to the combination of dimensional tolerances, the bite into the inner diameter of the groove may occur, so please do not cause the O-RING to bite during installation.
②Plane static seal
Flat static seals can be divided into two types: occasions with internal pressure and occasions with external pressure. In the case of internal pressure, in principle, the outer diameter of the O-ring is fitted, and in the case of external pressure, in principle, the inner diameter of the O-ring is fitted.
Since the crushing rate is usually not a problem during installation, it can be considered that the elongation of the bolt and the deformation of the flange surface after bearing the pressure are greater than that of the cylindrical static seal. In this case, since it is not attached to the wall, it may be worn or peeled off due to pressure changes, so please do not use it.
When the inner diameter is relatively large (above Φ 150) and the cut-off diameter is relatively thin (below Φ 3), there will be situations such as the O-ring flying out, clamping and part of the O-ring being trimmed as shown in Figure-5. Out, a thicker cut-off diameter can be used.
In the case of internal pressure, the D dimension is relatively small (below about Φ 30), and sometimes it is not suitable for installation. It is more convenient for the D dimension to be slightly larger (about 0.2 ~ 0.3mm).

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