A Seals isolate the oil chambers to prevent hydraulic fluid leakage and block external contaminants such as dust and dirt from entering the cylinder. Common types include O-rings, lip seals, and wiper seals. Seal performance directly affects the cylinder's leakage rate and service life, making proper seal selection and maintenance essential for reliable operation.

A Selection depends on working pressure, temperature, and hydraulic oil type. Nitrile rubber (NBR) suits low-pressure, normal-temperature applications. Fluorocarbon rubber (FKM) is chosen for high-pressure, high-temperature conditions. Polyurethane (PU) offers excellent wear resistance for abrasive environments. Chloroprene rubber is required when phosphate ester fluids are used. The material must be compatible with the fluid and withstand the expected operating conditions throughout the seal's service life.

A Seal failure results from multiple factors including natural aging, long-term friction wear, installation damage such as cuts or pinching, and contaminated oil containing abrasive particles that accelerate wear. High temperatures cause hardening and loss of elasticity. Additionally, mismatched seal type for the operating conditions and incorrect installation clearances can lead to premature failure and leakage.

A Lip-type wiper seals have a simple structure and are suitable for generally clean environments. Labyrinth-type wipers use multiple clearance gaps to block dust and are ideal for harsh, dusty environments such as construction and mining. Combination-type wipers integrate multiple sealing elements and are designed for high-pressure, high-dust applications. The choice depends on the severity of external contamination expected in service.

A Signs include visible oil leakage at the seal area, an oil film residue on the piston rod surface, pressure drop during operation, insufficient thrust or pull force, and noticeably slower movement speed. After ruling out other causes, these symptoms likely indicate worn, aged, or damaged seals. Replacement with the correct seal type should be performed promptly to restore performance.

A Piston rods are commonly made from 45# carbon steel or 27SiMn alloy structural steel. Stainless steel is used in corrosive environments. The surface undergoes quenching to increase hardness, followed by chrome plating or nitriding to form a wear-resistant, corrosion-resistant protective layer. Some applications also require polishing to further reduce seal wear and extend rod service life.

A Protection includes installing lip-type wiper seals to block external dust, fitting telescopic metal or rubber protective covers to prevent impact and foreign object damage, applying anti-corrosion coatings in corrosive environments, and regularly cleaning the rod surface to remove accumulated contaminants. Maintaining seal integrity prevents oil leakage that could lead to rod surface corrosion.

A Causes include external particle abrasion, worn chrome plating, contaminated oil, and humid or corrosive environments. Minor scratches can be polished smooth with fine sandpaper. Rust spots should be cleaned and coated with protective oil. Severely damaged rods require replacement. The contamination source must be identified and eliminated, with sealing and protective measures strengthened to prevent recurrence.

A Seal failure severely impacts cylinder operation. The seal ring is the most critical sealing element. With proper bore machining accuracy and surface roughness, plus a lubricating oil film, sealing performance is assured. While hydraulic pressure creates high contact stress between the seal and bore, friction is limited and axial displacement is small, so seals don't wear rapidly under normal conditions. However, seal failure often manifests as rubber extrusion under high pressure, where seal material gradually extrudes through the clearance gap, eventually causing complete failure.

A The sealing system uses a layered approach. The main seal layer employs step seals combining PTFE for low friction and high-pressure resistance with an O-ring for preload compensation. A wiper seal layer at the rod end uses double-lip designs—the first lip scrapes large particles, the second captures fine dust. A buffer seal layer at the cylinder end reduces impact pressure during high-speed piston deceleration. Seal materials include carbon-filled PTFE for high pressure and polyurethane for high speed. The rod surface is hard-chrome plated to at least 50 μm thickness with roughness Ra ≤ 0.2 μm, while the bore is honed to Ra ≤ 0.4 μm.