1.2.1 of surface tension of liquid sealing device for sealing a fluid theory mainly, and flows with surface tension. The formation of seal gap and the axis of the liquid film, is caused by the surface tension of the. EJJagger thinks: lubricating film of liquid surface tension is caused, due to fluid lubrication and capillary action, will make the fluid infiltration seal clearance. In the formation of curved side and air interface, surface tension will prevent fluid leakage through the clearance. Medium pressure and seal gap is inversely proportional to the /h type: p=2 Sigma in sigma is the surface tension; P is a medium pressure seal clearance; H. Depend on the surface tension of the oil film, lubricant retention in a certain position, forming a sealing barrier. In the state of motion, the influence of oil film thickness increases with the friction coupling of the relative velocity, the viscosity of the fluid, the contact surface pressure and many other factors change. The theory of 1.2.2 boundary lubrication which is used to illustrate the seal failure mechanism theory, that the sealing contact with the shaft, a boundary lubrication, hydrodynamic lubrication and mixed lubrication of 3 kinds of lubrication state. Many scholars think, reciprocating seal is sealed in the lubrication fluid dynamic. 1.2.3 hydrodynamic seal floating in the theory of fluid film on the polymer seal with sealing fluid dynamic pressure of different surface and surface as a rigid body, its characteristics like diaphragm interfacial film fluid pressure local support. Therefore, the prediction of film shape was established in reverse fluid dynamics theory based on the Reynolds equation, available to handle. Type U0 is in outside the piston stroke speed; P0 for internal pressure; H (x) as variable film height; variable liquid film pressure of fluid in the gap; ETA is the viscosity; h0* is the maximum pressure at the membrane with high. Assume that h in a values make |dp/dx| reach the maximum, so the type (1) for H and its derivative is 0, available h0*=2/3h, the substitution type (1): therefore, the gap between the fluid flow can be obtained by the oil film thickness, the leakage of the fluid dominated by |dp/dx|. If the piston rod reciprocating seal as an example, assume that the diameter of the piston rod is D, then the adhesive liquid volume flux in layman Cheng rod is: in the formula: UI as internal travel speed; Pi is an inner stroke liquid pressure; hi* as internal travel and high maximum pressure at the membrane. If the piston rod to do reciprocating motion of constant velocity u, stroke of the piston rod is H, a period T t/2 and expert include lay Cheng Cheng t/2, outer stroke oil leakage, flow rate of V0: the stroke of the oil is brought into, flow rate of Vi, is a period of oil net leakage: therefore, the oil does not occur leakage condition is: due to the structural shape and material seal and deformation, and the deformation will affect the oil film pressure. Therefore, the reasonable design of the shape and the preload pressure sealing position, can improve the seal of the seal and the friction performance. Development and application of 2 design methods of hydraulic reciprocating seal 2.1 hydraulic reciprocating seal for the hydraulic reciprocating seal are contact type seal, seals to follow the sliding surface due to roughness, waviness shape tolerances, caused by the elastic deformation of the sealing gap changes, or due to load changes so that the piston (or rod) and the cylinder liner deformation arising from the seal clearance variation, leak channel to block. The rubber seal main sealing element for good resiliency as reciprocating seal. In order to make the type (7) always established for reciprocating seal, rubber seals should be designed with different cross-sectional shapes. However, good elastic rubber seals are often poor wear resistance, so the new seal combination, including the combination of the structure and materials of the seal has become the main form of reciprocating seal seal.
Around this issue, different scholars have conducted a lot of research from different angles, and put forward a lot of dynamic seal theory, the following introduces several typical theory of hydraulic reciprocating seal.
