Basic Properties Of Hydraulic Seals

The performance of hydraulic seals is mainly reflected in the quality of hydraulic components and hydraulic systems. The main indicators of evaluation are tightness, life, environmental adaptability, range of use conditions, reliability and safety.
(1) Sealing capacity
First of all, the seal and the sealing device are required to have a sealing ability for the liquid, that is, it can seal the liquid fluid in the closed chamber without allowing the liquid fluid to flow out or leak out of the chamber. Static sealing can be done and dynamic sealing should not be done. This gives rise to the concept of the amount of liquid fluid outflow or leakage, that is, the advantage of using the concept of tightness to reflect the ability of a certain hydraulic seal. The so-called sealing degree is the amount of volume or mass of leaked liquid per unit time. At present, the sealing capacity of the sealing device is good for the dynamic seal, or to evaluate the advantages and disadvantages of its sealing performance.
(2) Sealing life
Although the life of seals or sealing devices is affected by many factors, such as their material, use environment and working conditions, not only the length of time of the effectiveness of seals or sealing devices is calculated as his life. That is, when it is used in hydraulic components or hydraulic systems, its seal is effective, that is, the leakage is within the specified "allowable leakage rate"; Until the specified (after maintenance) "allowable leakage" is exceeded. This period is the life of the seal or sealing device. At present, the longest life can be up to 10 years, the general life of seals and sealing devices is about 3 months to 1 year, slightly longer, no doubt longer sealing life is better. In the same hydraulic sealing system, the actual sealing effective time of the seals and sealing devices at different places needs to be as consistent or similar as possible. The wear and damage of seals and sealing devices will affect the sealing effectiveness. If you want to have a long life, the material of the seal should have a certain strength, stiffness and hardness, requiring low wear factor and good elasticity. The dynamic seal should also have better lubrication conditions, and the seal structure should also have a reasonable geometry, and there should be no defects.
(3) Environmental adaptability
The so-called environment refers to indoor and outdoor, continental or ocean, tropical or cold zone, dry or humid, space with sand, dust or clean no wind, corrosive gases or clean and harmless air, direct sunlight strong or weak oh, whether there is ozone and so on. This should consider whether the seal or seal device is suitable in such an environment, whether it affects its seal and the life of the seal or seal device. For example, in the cold zone, the material of some seals may become hard or even crack; If subjected to strong direct sunlight or ozone, some sealing materials are easy to age; If the material in the tropics for a long time may become soft. If these seals can not adapt to the environment in which it is located, its sealing performance will be reduced and its life will be shortened, so it is necessary to consider the adaptation of the sealing environment.
(4) Conditions of use
Any seal or sealing device is not in any working conditions (working conditions) have a sealing ability, but only in the specified working conditions, that is, under the specified working conditions, the seal or sealing device has a sealing ability - to prevent the leakage of the fluid working medium in the closed chamber, to prevent external dust, foreign matter into the closed chamber. The so-called working conditions refer to the working medium, working pressure, working temperature, and working speed. Any seal or sealing device must meet these four conditions.
a, liquid fluid medium seal or sealing device parts material and liquid fluid medium must have compatibility, that is, any part of the seal or sealing device and liquid fluid phase contact, maintain its chemical stability, physical invariance. That is, when the parts of the seal and the sealing device are in contact with the liquid fluid medium, no chemical or physical changes occur, and the mechanical properties, mechanical strength, hardness, elasticity, softness, etc. remain unchanged.
b, working pressure is one of the main parameters in hydraulic technology, pressure difference is the main reason for leakage, especially interface leakage, and sealing is to prevent leakage. Therefore, it is necessary to know how much pressure (pressure difference) the sealing device can seal the liquid in the hydraulic component, that is, to cut off the flow channel of the hydraulic medium and prevent leakage.
c, the working temperature to the present dynamic seals and sealing devices can adapt to the temperature range of -240-500 ℃, static seals and sealing devices can adapt to the temperature range of -240-900 ℃. Be careful to note that specific seals and sealing devices have specific temperature ranges that can be adapted to.
d, the working speed of the contact seal in the dynamic seal, the working speed will have a great impact on the sealing performance. Because it seriously affects the friction and wear of seals or sealing devices. Not only that, friction generates heat and produces thermal effects. These will affect the effectiveness of the seal or seal device, resulting in premature seal failure, so it is necessary to consider the speed range that the seal and seal device can adapt under the normal service life. The working speed of general seals and sealing devices is 0.01-5m /s, and in very few cases the working speed can reach 15m/s, or even 100m/s.