Classification and Selection of Hydraulic Seals
The commonly used hydraulic seals for hydraulic cylinders mainly include O-rings, lip seals, and combination seals.
1. O-ring seals
O-rings have an O-shaped cross section, a simple shape, and are made of rubber. Their wear resistance is not as good as that of polyurethane, so they are mainly used for static sealing in hydraulic systems.
2. Lip Seals
U-shaped seals: U-shaped seals offer good sealing performance, but they are prone to rolling when used alone. Their frictional resistance is high and increases with working pressure. Therefore, U-shaped seals are only suitable for hydraulic cylinders with low working pressure or low operating speed.
V-shaped seals: V-shaped seals must be used in conjunction with support rings and pressure rings. They offer good sealing performance, and the number of seals used can be determined based on the working pressure. Wear of the seals can be compensated by adjusting the pressure ring. The disadvantage of V-shaped seals is their complex structure and high frictional resistance. Therefore, V-shaped seals are only suitable for hydraulic cylinders with low operating speed and high working pressure.
YX-shaped seals: YX-shaped seals have a width-to-height ratio greater than 2. Based on the requirement for stability, the working lip of the YX-shaped seal is shorter than the non-working lip. This results in YX-shaped seals for bores and shafts. YX-shaped seals do not roll during use, making them suitable for high-pressure, high-speed hydraulic cylinders.
3. Combined Seals
O-rings: O-rings are composed of a synthetic rubber O-ring and a fabric-reinforced rubber Y-ring. They rely on their own deformation to generate high initial contact stress on the sealing surface, preventing leakage of unpressurized fluid. When the hydraulic cylinder is working, the pressurized oil causes the O-ring to elastically deform, constantly squeezing and expanding the sealing lip of the Y-ring, making it tightly adhere to the sealing surface. This, together with the initial contact stress, prevents pressurized oil leakage.
Glyd rings: Glyd rings are composed of an O-ring rubber seal and a square seal filled with PTFE. Glyd rings can be divided into bore Glyd rings and shaft Glyd rings, but their sealing mechanism is the same: their deformation generates high initial contact stress on the sealing surface, preventing leakage of unpressurized fluid. When the hydraulic cylinder is working, the pressurized oil causes the elastic deformation of the O-ring to compress the square seal, making it tightly adhere to the sealing surface, and together with the initial contact stress, it prevents leakage of pressurized oil.
Step seals: Step seals have a similar structure to Glyd rings, also composed of an O-ring rubber seal and a specially shaped rectangular or trapezoidal seal filled with PTFE. Like Glyd rings, step seals can be divided into bore step seals and shaft step seals. The sealing function and sealing mechanism of step seals are the same as Glyd rings, but step seals only have a unidirectional sealing effect. Both step seals and Glyd rings are characterized by being filled with PTFE, resulting in low friction, no creep, and long service life.