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1. Preparation before installation
- 1. Inspect the Seal and Hydraulic Cylinder
Before installing the seal, carefully inspect its appearance. Check for burrs, cracks, cut edges, porosity, or other defects. The seal’s dimensions and precision must meet standard requirements. Also, check the hydraulic cylinder’s inner wall for smoothness, scratches, and rust. If any problems are found, address them promptly.
- 2. Cleaning
Thoroughly clean the hydraulic cylinder and seal to remove dust, oil, and other impurities. Use a clean cloth or detergent to ensure a clean installation environment.
- 3. Prepare Installation Tools
Prepare the necessary tools for installing the seal, such as a wrench, screwdriver, and rubber mallet. Ensure the quality and suitability of these tools for a smooth installation.
2. Installation Process and Precautions
The hole seal assembly consists of an O-ring and a wear ring (see Figure 1).
O-rings are relatively elastic and easy to install. Wear rings, on the other hand, are less elastic. If installed directly, the piston’s steps and grooves could easily scratch the sealing surface, affecting the sealing effect. To ensure the wear rings are not damaged during installation, certain installation precautions should be taken. Wear rings are primarily made of polytetrafluoroethylene (PTFE)-filled material, which is corrosion-resistant and has a high coefficient of thermal expansion. Therefore, before installation, they should be soaked in 100°C oil for 20 minutes to soften them. Then, they should be installed into the piston groove using the tooling shown in Figure 2.
The tooling shown in Figure 2 consists of a positioning sleeve and an expansion sleeve. The positioning sleeve has a 5° chamfer on its head to guide the O-ring and wear ring into the piston end groove. The expansion sleeve is made of 65Mn steel with good elasticity and heat-treated, machined into a uniform and symmetrical eight-petal structure. It is important to ensure uniform indexing when machining the small holes at the bottom of each petal. When milling each petal, align the saw blade with the center of the hole to ensure uniform expansion of the petals. All parts should also be chamfered (smoothly) to avoid damaging the sealing ring.
Each seal size requires a corresponding tooling set to ensure proper assembly. After installation, the seal must not be wrinkled, twisted, scratched, or installed upside down.
Another type of seal is the polyurethane Y-ring, widely used in hydraulic cylinders due to its high hardness, high elasticity, oil resistance, wear resistance, and low-temperature resistance. Its inner and outer lips can be shaped with unequal heights depending on whether it is intended for shaft or bore use, providing both sealing and self-protection. The short lip of the unequal-lip Y-ring contacts the sealing surface, resulting in low sliding friction, excellent wear resistance, and long service life. The long lip maintains a high pre-compression against the non-moving surface, preventing movement during operation.
Due to the high hardness and high pre-compression of polyurethane Y-rings, installation and replacement often result in damage such as squeezing, curling, and undercutting, resulting in ineffective sealing or even failure. During assembly, we previously used a screwdriver to press the sealing lip inward along the cylinder bore; or we used thin wire to tighten the outer lip of the sealing ring so that its outer diameter was smaller than the cylinder’s inner diameter, inserting the sealing ring into the cylinder, and then withdrawing the wire. However, both installation methods can easily scratch the sealing ring, causing seal failure and increasing repair time. To address this issue, we cut 0.1mm thick cold-rolled steel strip or copper sheet into a rectangular shape, the length of which equals the circumference of the Y-ring’s outer diameter. We then use this strip to wrap the sealing ring tightly and gradually insert it into the cylinder barrel. Once the outer lip is fully seated, we withdraw the ring, achieving better installation results.
3.Inspection after installation
- 1. Check the Sealing
After installation, the hydraulic cylinder needs to be inspected for sealing. A pressure test or leak detection can be performed to verify proper installation of the sealing ring and any leakage.
- 2. Check the Operation
During operation, carefully observe the hydraulic cylinder for any abnormal noise, vibration, or leakage. If any problems are detected, immediately shut down the machine for inspection, identify the cause, and address them.
