Fluid seals used mainly three categories, namely O-ring, Reciprocating and rotary shaft lip seal with a lip seal (oil seal). Structural design of rubber seals of the sealing mechanism and its applications are closely related. O-ring and the class of O-ring O-ring seal is a cross-section was circular annular seal, in all seal products is the largest production, standardization and serialization of the highest degree, a class using the most sophisticated sealing products . O-ring seal in the fluid state of their work can be divided into static and dynamic seals seal. From the perspective of polymer, rubber O-ring seal material behavior is similar to the high viscosity fluid, it has come in contact with the pressure delivered to the surface features. When the O-ring installed in the trench to a certain extent by the compression section (usually 8% -25%), they produce an initial contact stress. Was sealed in the fluid (air, water, oil) is very low or zero pressure case, the fluid pressure in the high-, O-ring is pressed with the pressure in the opposite direction to the side of the trench corner and produce plug flow reveal the stress distribution channel, play a role in sealing. That the fluid pressure in large, sealed O-ring contact pressure is equal to the initial contact stress and fluid pressure generated by the sum of the contact stress. Contact pressure is always slightly larger than the liquid pressure of work, so greatly enhancing the sealing effect. When the O-ring seal for reciprocating motion, the sealing mechanism is also self-sealing effect. However, due to O-ring is in motion, and fluid pressure is applied alternately O-ring sides, so the process is extremely complex. Experiments by rod seals, the basic understanding of the reciprocating motion of O-ring seal and leakage mechanism. If the O-ring and the shaft surface magnification, the surface is uneven, especially the O-ring contact surface is convex at its contacts with the shaft. When the shaft began to move to the right, the axis with the liquid adhesive into the O-ring and the narrow wedge between the shaft area, this part of the liquid pressure will be greater than the working fluid pressure. If the pressure is greater than the contact pressure O-ring, O-ring would be from the top of the liquid penetrated into the recesses, resulting in leakage. When the axial movement of the opposite direction, the direction of movement due to the pressure axis in the opposite direction, the direction of motion along the axis to reduce leakage, the difference between a reciprocating motion to form a leak to the outside. In general, the greater the liquid viscosity, shaft speed the greater the effect that the greater the slip, the more serious leak. O-ring seals in the dynamics there are two major shortcomings, namely, to reverse the damage and the initial dynamic friction greatly. To overcome these two defects in the non-circular cross-section O-ring and the complex structure of O-ring. For example: O-ring is the main square or rectangular ring substitutes, are common in the static seal. In the dynamic O-ring seal in and compared the advantage that completely fill the groove section, so when the pressure of the mechanical displacement of alternating small; its anti-extrusion capacity to reverse the damage and the friction contact surface due to its large, it only applies to low-speed reciprocating motion, is not suitable for rotation. Also, according to the use of different needs, as well as D-ring, triangle ring, diamond ring, X ring, H-ring and so on. Seal lip and dust lip seal ring is compressed and a pressure enhancement was lip seal or a class of seal gasket. Many of its structure, in addition to the standard V-shaped, U-shaped, Y-shaped, L-shaped and J-shaped, there are evolved from these forms of special shapes. Mainly in the material of rubber or rubber cloth; PTFE is used in some chemical manufacturing equipment; metal material is in the above materials can not meet the requirements of the occasion, such as ultra high temperature, ultra-low temperature and nuclear radiation environment. Such lip seal reciprocating motion generally limited to use, but some types can also be used for static or rotating seals. Lip seals installed in the absence of outside pressure in the groove, when the piston rod or cylinder wall sealing lip compression by generating an initial contact pressure. External pressure, the lip seal sealing lip is pressed to the surface to be sealed, the pressure to pass through the liner to its contact point on the lip contact point of the pressure is always greater than the fluid pressure, thus preventing fluid leakage. Both lip seals have a high pressure or low pressure sealing efficiency, but also wear a certain compensation, will not cause leaks soon. Dust ring is a special seals, hydraulic and pneumatic cylinders it is not as the primary sealing surface and used as a dust-proof device for removal of leakage in reciprocating piston rod outside the cylinder attachment on the part of the surface dust, dirt, dust, dirt, rain and frost, etc., to ensure that internal machinery clean. Dust ring of rectangular cross-section for the most simple, the material is often felt, hard rubber or other semi-rigid elastic material. Use need to impose pre-load, dust effects depend on the size and pre-load ring face the nature of the dust. However, as the load increased, though the role of the wipe, but it also increases the friction and wear. Rotary shaft seal seal seal is the most important species, also known as radial lip seals. Its main use is through the flexible seal lip contacts with the shaft or housing to prevent leakage of bearing lubricant, but also through it to prevent external dust and mud and other foreign matter intrusion. Seal assembly use, the sharp edge in the radial sealing force will be under the contacts with the minor axis of deformation, when the shaft rotation into a deformed part of the rapid wear of a certain width to be flat (a process known as SEAL The adjustments, shall be completed in a very short period of time), through this flat can be controlled in boundary lubrication film (thickness of about 0.0025mm), to prevent the oil leakage. Oil seal oil seal lip material properties of work performance on a very important influence. Which determines the operating temperature range of oil seals, friction, wear resistance, dielectric properties and sealing properties. Therefore, as a rubber seal lip material, in addition to meet the appropriate mechanical strength and hardness, high temperature resistance, resistance to the working media and other general requirements must also be flexible so that it has a good run on the axis of the shaft follow the good and the irregularity of the axis, eccentricity and vibration have a good ability to compensate. At the same time highly flexible sealing lips are sealed on the shaft radial force required is also small, which can decrease the friction and the friction and heat. Seal is characterized by fluid dynamics at the axis with the fluid dynamic effects at the same time, that can resist the leakage flow viscous shear force, the leakage of oil to the oil chamber loopback direction. Return back to the oil shear force or thrust is generated by the air side of the lip seal face additional raised or sunken patterns, such as oblique stripes, round or semi-circular patterns, wave patterns and so on. The uniform pattern in the lip and the lip tangent, so the lip in contact with the shaft surface to form a smooth contact not only with, but also from the contact zone with the axis of the contact angle to branch area. When high-speed rotation axis, these patterns will be the same as the screw into the air to leak through the edge back to the oil side of the pump chamber, thus avoiding leakage of oil from the seal to an external site.

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