The role of hydraulic seals in hydraulic parts

In the hydraulic system, the hydraulic cylinder is the power transmission element. In the hydraulic cylinder, the sealing ring selected on the piston and the guide sleeve is very important for the hydraulic cylinder to complete the specified function under the specified conditions and within the specified time, and keep its performance within the allowable range. . If the hydraulic seal fails prematurely, the power transmission function must be lost. In modern design, reasonable selection of hydraulic seals and reasonable structural design are necessary conditions to ensure product performance and improve product quality.

As we all know, seals play an important role in hydraulic components. Different hydraulic seals have different sealing properties. We take the hydraulic cylinder as an example. The most common and typical sealing forms include Step seal, Yx sealing ring, O-ring, etc. These hydraulic seals are used in hydraulic cylinders, and their main function is to ensure that the linear reciprocating components axial seal. When the pressure increases in a lower range, the Yx seal will be in a sub-tight state, at this time, the leakage Q of hydraulic oil through the gap is also very small, almost zero. This is because at a lower pressure, the gap formed between the seal and the mating pair of the metal part makes the pressure difference decay to zero over the entire length of the contact surface between the seal and the metal.

When the pressure of the hydraulic cylinder is gradually increased, the sealing performance enters the hollow area. In a certain pressure range, a larger leakage is formed. This is because as the pressure increases, the pressure difference decreases over the entire length of the sealing surface beyond the pressure attenuation that the sealing surface can accommodate, and a large leakage occurs in a short period of time.

When the pressure acting on the hydraulic cylinder gradually increases, and the output force generated by the pressure is balanced with its external load, the hydraulic cylinder is in a normal working state, and the leakage of the contact surface between the seal and the metal part conforms to a certain law. The increase shows a linear increase in leakage.

If the hydraulic cylinder works above the maximum pressure that the seal can withstand for a long time, its sealing performance will be damaged, and leakage beyond the specified amount will result in permanent failure.

The above four areas are common, but the structure of the hydraulic seal is different from the sealing form, and it shows that the area drifts toward the increase or decrease of the pressure value.

Since hydraulic seals have the above characteristics, how to use the seal to avoid large leakage, ensure its normal performance and use more reliably will be the issue we want to discuss.

Assume that under the specified conditions (temperature, pressure, oil medium, etc.) within the specified time limit, when the O-ring and Yx sealing ring are used for the guide sleeve, the respective reliability is: Ro=0.97, Ryx=0.98. Then the reliability of the composite seal is:

Comparing R with Ro and Ryx, we can see that its reliability is significantly improved after compound use, and the possibility of failure of the product within a specified time under specified conditions is reduced from the original 2% to 6/10,000. In other words, the composite design will have a longer lifetime, allowing for a certain failure rate.

As above, we elaborated and analyzed the sealing and reliability of the hydraulic cylinder. On the basis of mastering the characteristics of seals, with the reliability theory as the guiding ideology, rationally designing the sealing structure of hydraulic cylinders is a typical feature of modern design to improve product quality. The reasonable application of reliability technology is not only beneficial to guarantee the basic performance of the product, but also enables the product to have a better guarantee ability to complete the specified tasks under the specified conditions.