(1) gap clearance seal sealed sealing is a commonly used method, it relies on the relative motion part of the small gap between the mating surfaces to prevent leakage from the circular flow theory shows that the axial gap, and the leakage is proportional to the cube of the gap, so reduce the gap approach can be used to reduce leakage. General clearance is 0.01 ~ 0.05mm, with the surface which requires a high precision. Cylindrical surface of the piston to open several channel width generally 0.3 ~ 0.5mm, depth 0.5 ~ lmm, 2 ~ 5mm pitch ring groove, said balance tank, and its role as follows: (a) performance of the piston seal; (c) self- lubrication, oil storage tank in the balance, so that the piston can be automatically lubricated. Clearance seal is characterized by simple structure, small friction, durable, but high precision machining, and difficult to completely eliminate the leakage. It only applies to low pressure, small diameter cylinder fast. (2) piston ring seal mounted on the piston ring piston ring seal to rely on flexible metal ring-shaped tank close to the cylinder wall to achieve sealing. It was better than clearance seal the seal is good, apply a wide range of pressure and temperature, can automatically compensate for wear and temperature changes, can work under conditions of high speed, friction is small, reliable, long life, but not completely sealed. Processing complex piston ring, cylinder barrel high precision surface processing, are generally used for high pressure, high-speed and high temperature applications. (3) ring seal ring seals are the most widely used in the hydraulic system of a seal ring with O-shaped, V-shaped, Y-shaped and combined and several species of the material for the oil and rubber, nylon, polyurethane and so on.
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