Hydraulic cylinders play a vital role in hydraulic equipment, and their failures directly impact operational efficiency and service life. Extensive field experience demonstrates that cylinder failures primarily manifest as leakage (internal and external), mainly caused by damage to the following components: seal failure, end cover bolt failure, guide sleeve wear, and piston support ring wear. Notably, the latter three types of damage ultimately lead to seal failure. Based on years of cylinder repair experience, we analyze seal failure causes and propose improvement solutions.

1. O-ring Failure Caused by Improper Installation Type

Sometimes, designers adopt corner seals or end face seal types for O-rings, considering factors such as assembly, installation, technology, and component strength. However, we believe this sealing type is unsuitable for medium and high-pressure hydraulic cylinders because its sealing effect relies mainly on the clamping force from tie rods or screws. As the hydraulic cylinder operates over time or under increasing pressure, screws may loosen or tie rods may stretch, reducing clamping force and causing leakage. Additionally, uneven tightening of screws can also lead to leakage. While this can be mitigated by evenly tightening screws or adding anti-loosening devices on nuts, it is preferable to replace end face or corner seals with circumferential seals.

2. Failure of End Cover Screws

After regular inspection or replacement of the sealing ring, hydraulic cylinders often leak due to damaged cover screws within two to three days of restarting. This failure typically occurs because the cylinder is put into operation immediately after disassembly and assembly. Although screws are evenly tightened during assembly, actual clamping forces vary due to different roughness on screw mating surfaces, leaving some screws in a pseudo-fastened state. Thus, screws bear uneven forces during operation. If there is a clamping margin between the cover and cylinder flange and screws are not fully tightened, this issue becomes more pronounced, leading to sequential screw damage. The solution is: do not put the cylinder into formal operation immediately after assembly. Instead, apply pressure first, then retighten the screws while ensuring uniform clamping force. If a gap must be left, insert a suitable gasket before fully tightening the screws.

3. Rapid Seal Damage Caused by Excessive Wear of Guide Sleeves and Piston Support Rings

When a hydraulic cylinder fails to achieve the specified output force due to leakage, the primary cause is usually damage to the seals on the piston rod. Frequent seal damage stems from excessive wear of guide sleeves and piston support rings. When the dynamic fit clearance between the guide sleeve and piston rod or between the piston support ring and cylinder barrel exceeds a certain limit, it not only accelerates seal wear but can also cause cylinder instability and piston rod bending. Therefore, worn guide sleeves and piston support rings must be repaired or replaced. Generally, severely worn guide sleeves and pistons should be replaced. However, for large hydraulic cylinders, guide sleeves and pistons are often made of cast iron or copper surfacing parts. Replacing the entire component is not only costly and wasteful but also difficult to machine.