Technical requirements for hydraulic seals and hydraulic seal structure and mechanism
Dec 06, 2022
Performance of hydraulic seals
Very small leakage
Hydraulic seals are required to have minimal leakage, good sealing action and automatically improve their sealing action as the pressure of the hydraulic oil increases, even under harsh working conditions such as high pressure and high temperature, with no significant increase in leakage.
Good compatibility
As hydraulic seals are immersed in hydraulic oil for a long time, they are susceptible to swelling, dissolution or brittle hardening, etc., which causes them to lose their sealing effect, and therefore require good compatibility with hydraulic oil.
Low frictional resistance
In order to avoid or reduce undesirable phenomena such as low pressure crawling in hydraulic equipment, hydraulic seals are required to have low static and dynamic frictional resistance, and their coefficient of friction should be very stable.
Long service life
Hydraulic seals should have good elasticity, heat resistance, cold resistance, pressure resistance, wear resistance and a certain physical and mechanical strength, and have a long service life.
Low price
Hydraulic seals should be easy to manufacture and install, their corresponding sealing grooves are easy to process and manufacture, and the requirements for processing accuracy of sealing surfaces are low and inexpensive.
Structural forms and sealing mechanisms of hydraulic seals
Commonly used self-sealing compression hydraulic seals are mainly O-rings, round seals and square seals, which have the advantages of simple structure, easy manufacture and low cost, so they are widely used as dynamic sealing elements and static sealing elements in hydraulic transmission systems. They are installed in the seal groove usually produce 10-25% of the radial compression deformation, and seal the surface to produce a higher initial contact stress, thus preventing the leakage of non-pressure fluid. When a hydraulic cylinder is in operation, the pressure fluid squeezes the self-sealing compression hydraulic seal, deforming it further and generating a higher pressure on the sealing surface with the pressure fluid, which should be strictly speaking a compressive force. The additional contact stress increases and together with the initial contact stress stops the leakage of the pressure fluid. However, when the working pressure is greater than 10Mp, in order to avoid a part of the synthetic rubber self-sealing hydraulic seal being squeezed into the sealing gap and cut off in the reciprocating movement of the hydraulic cylinder and causing leakage, a synthetic resin retaining ring, such as nylon retaining ring, polyformaldehyde retaining ring and filled PTFE retaining ring, must be set on each side of the synthetic rubber self-sealing hydraulic seal under pressure.
Due to the large compression deformation of the synthetic rubber self-closing hydraulic seals, the static frictional resistance is particularly high, usually more than twice as high as the dynamic frictional resistance. Such high static frictional resistance is bound to cause low pressure creep and operational difficulties in some low pressure hydraulic transmission systems, which is why self-sealing compression hydraulic seals are rarely used as dynamic seals alone.
Lip seals
At present, the hydraulic combination seals commonly used in hydraulic cylinders in ceramic plants are mainly composed of O-shaped seals and square seals, U-shaped seals, Y-shaped seals, YX-shaped seals < and other special shapes of hydraulic seals used in superposition.
