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Composite seals are composed of two or more components. Some are components with good lubrication properties and a low coefficient of friction ； The other part acts as an elastomeric element, thereby **improving the overall sealing performance**. I. Coaxial seal ring: A coaxial seal ring is a sealing element designed for reciprocating motion, with its structure and materials combined into a single unit. It is composed of a modified polytetrafluoroethylene slip ring with filler material, combined with rubber rings that serve as elastomers (such as O-rings, rectangular rings, star-shaped rings, etc.). Based on their application, they can be divided into coaxial seals for pistons (Gland rings combined with O-rings) and coaxial seals for piston rods (Stearic rings combined with O-rings). Their structural formats are shown in the figure below. Both Gland rings and Stearic rings are made from polytetrafluoroethylene resin as the base material, with fillers such as copper powder, graphite, carbon fibers, asbestos, molybdenum disulfide, clay, etc., added in varying proportions depending on the specific usage conditions. Due to the self-lubricating properties of polytetrafluoroethylene resin, the coaxial seal ring is one of those with the lowest dynamic frictional resistance among various types of reciprocating motion seals, as shown in the figure below: 1. Features: The coaxial seal ring takes advantage of the good elastic deformation properties of the O-ring; through its pre-compression force, it presses the sealing ring tightly against the sealing surface to achieve a sealing effect. The O-ring does not come into direct contact with the sealing surface, so there are no issues such as the ring flipping, twisting, or being squeezed into gaps. Therefore, coaxial sealing rings have the following characteristics: 1) The Groeneveld ring and Stellite ring have an extremely low coefficient of friction (0.02~0.04), with little variation in the dynamic and static coefficients of friction. Therefore, the movement is smooth with no crawling ； 2) It has good self-lubricating properties, and does not easily stick to metal mating surfaces ； 3) Good sealing performance ； 4) Depending on the operating conditions, the ratio and type of polytetrafluoroethylene resin filler can be adjusted to achieve the desired physical properties. 2. There are **standards** in place for the size series and tolerances of coaxial seals, as well as for the shapes, sizes, and tolerances of the installation grooves. These standards are GB/T15242.1—2001 \"Size series and tolerances of coaxial seals for dynamic sealing devices of hydraulic cylinder pistons and rod pins\", and GB/T15242.3—2001 \"Size series and tolerances of installation grooves for coaxial seals used in dynamic sealing devices of hydraulic cylinder pistons and rod pins\". Coaxial sealing rings have been widely used in the reciprocating motion sealing devices of medium and high-pressure hydraulic cylinders. Its application range is: operating pressure not exceeding 50 MPa ； The movement speed shall not exceed 1 m/s ； Operating temperature: -30°C to +120°C. When using a coaxial seal ring, the selection of the fit clearance at the sealing interface is related to the pressure level of the working medium. To prevent the Graetz rings and Stetson rings from being squeezed into the gap of the sealed coupling surface, the gap size must be controlled strictly in accordance with the requirements specified in the standards. Furthermore, the quality of sealing performance is also affected by the machining precision and surface roughness of the coupling surfaces, which should be given due attention. II. T-shaped Turcon grid ring: The T-shaped Turcon grid ring builds on the excellent properties of traditional elastomeric force-applying seals by improving their geometric weaknesses, thereby enabling precise positioning of hydraulic cylinders under load. Its material is Turcon. This new type of seal ring has a simple and compact structure, and it allows for a larger gap between the piston and the hydraulic cylinder wall. 1. The interface shape formed by the T-shaped grid and its stress distribution at the contact points are shown in the figure below. The T-shaped Turcon grid has the following characteristics: 1) It exhibits excellent static sealing performance ； 2) It allows for a larger clearance, thus reducing processing costs and enabling safe use in contaminated media ； 3) Low friction, no crawling ； 4) Various materials can be used, offering strong adaptability to working conditions ； 5) It can be used with the latest environmentally friendly and safe hydraulic fluids (bio-oils). 2. The use of T-shaped grids results in grooves with a simple shape, and the dimensions of these grooves comply with the ISO7425/1 standard; they can be used for integral piston seals. The working pressure shall not exceed 80 MPa ； The working speed shall not exceed 1.5 m/s ； Operating temperature: -54~+200°C. Application examples are shown in the figure below: III. HPR-type Turcon gasket The HPR-type Turcon gasket sealing device assembles the nitrile rubber elastomer, polyurethane retainer ring, and Turcon gasket together in an overlapping manner, thereby creating a lightweight sealing structure within a single groove that exhibits excellent performance, as shown in the figure below: 1. Features The nitrile rubber elastomer 2 in the gasket serves as a uniformly shaped pressure-relief ring, which exerts force radially on the polyurethane retainer ring 3 and the Turcon gasket 1. The HPR-type Turcon ring seal device, serving as the primary seal, possesses pressure-applying capability to prevent pressure buildup between the sealing elements. When the piston rod extends, the HPR type seal ring provides a sufficient lubricating film for the downstream support elements and secondary seals; the uniform geometry of the seal ring enables a suction effect when the piston rod retracts, thereby also controlling the lubrication condition. The advantages of this sealing device are: 1) The sealing component is lightweight and easy to install ； 2) Strong resistance to extrusion, capable of accommodating larger fit clearances, with good dimensional adaptability ； 3) Five adhesion forces ensure reliable operation over long stroke distances ； 4) Pollution resistance and good compatibility with fluids ； 5) Low friction, good wear resistance, and stable performance ； 6) It has pressure-relief capability. 2. The HPR-type Turcon grid is used for one-way sealing in hydraulic reciprocating or screw motions, featuring an integrated groove structure. The working pressure shall not exceed 50 MPa ； The working speed shall not exceed 1.5 m/s ； Operating temperature -54~+135℃ ； Work deadline: Petroleum-based hydraulic oils, water-ethylene glycol. IV. Composite sealing gasket: A composite sealing gasket is a sealing element formed by the integral bonding and vulcanization of a rubber ring and a metal ring, as shown in the figure below. The metal outer ring of the gasket provides support, while the rubber inner ring performs the sealing function after undergoing compression deformation. The difference between the inner ring thickness h and the outer ring thickness s is the amount of compression of the rubber. The advantage of the combined gasket design is reliable sealing and low axial compression force during connection. It can handle high fluid pressures and does not require additional sealing grooves, which makes it widely used. Suitable for static seals with a working pressure not exceeding 100 MPa and a working temperature range of -30 to +200°C.