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The sealing performance of O ring in reciprocating movement

Update:2018-10-10

In the seal systems of hydraulic rotating and pneumatic components, reciprocating seal is the common sealing requirements. Reciprocating seals are used in the cylinder, pneumatic cylinder, piston, cylinder block, piston rod, cylinder cover. The cylinder forms a gap with the cylindrical rod, and the piston rod moves axially within the bore. 

The action of the seal limits the axial leakage of the sealing medium. In the reciprocating seal, the sealing effect and self-sealing effect of the O-ring are the same as the static seal. Because of the elastic force of the O-ring seal itself, it can automatically compensate for the sealing ability after wear. 

However, when the liquid medium is sealed, the working condition is more complicated than that of the static sealing due to the movement speed of the shaft, the pressure of the liquid, and the viscosity.

When the liquid sealing medium is under pressure, the liquid sealing medium molecules interact with the metal surface, and the polar molecules contained in the oil are closely and neatly arranged on the metal surface, forming a strong bond between the sliding surface and the sealing member. 

The oil film is bordered and the multi-slip sealing surface creates adhesion. The oil film is always present between the seal and the reciprocating surface. In addition to lubricating the moving sealing surface, the oil film also has a sealing effect. However, when the shaft in the reciprocating motion is retracted into the cylinder, the oil film is retained by the seal outside the cylinder. 

As the number of reciprocating processes increases, the more sealing medium that remains on the outside of the cylinder, the later the oil droplets are formed, which is the cause of leakage of the reciprocating seal. The viscosity of the hydraulic oil decreases with the increase of temperature, and the thickness of the oil film decreases accordingly. 

Therefore, when the hydraulic equipment starts up at low temperature, the leakage amount is large, and the temperature rises with various reasons during the movement, and the leakage amount gradually decrease.