| 1 | Hydraulic U-cup seal | Hydraulic cylinder rod or piston | Polyurethane (PU) | High wear and extrusion resistance in many hydraulic applications | Often suitable for mineral-based hydraulic oils; check the specific compound for other fluids | Dynamic sealing where pressure and repeated movement are present | Match the seal profile, dimensions, pressure, and groove to the cylinder design |
| 2 | O-ring | Static joints, plugs, and selected cylinder interfaces | Nitrile rubber (NBR) | Good general-purpose service when correctly sized and installed | Commonly compatible with mineral oils; generally unsuitable for many phosphate-ester fluids | Simple, compact static sealing in conventional hydraulic systems | Choose the correct cross-section and hardness; avoid twisting or pinching during assembly |
| 3 | Rod seal | At the point where the piston rod exits the cylinder | PU or NBR, depending on design | High when matched to the rod finish, pressure, and movement | Compatibility depends on the compound; mineral-oil service is common | Limiting hydraulic-fluid leakage along a moving rod | Inspect the rod for scratches, corrosion, and excessive runout that can damage the seal |
| 4 | Piston seal | Between the piston and cylinder bore | PU or NBR; some designs use PTFE-based sealing elements | High in a correctly designed cylinder; varies by seal profile and operating conditions | Verify the exact material against the hydraulic fluid and any additives | Maintaining pressure separation across the moving piston | Confirm bore size, piston groove, pressure direction, and whether a single- or double-acting design is required |
| 5 | Wiper or scraper seal | Cylinder opening, outside the rod seal | PU or NBR | Good resistance to dirt and repeated wiping when properly fitted | Usually selected for external contamination control; fluid resistance still depends on the compound | Keeping dust, grit, and moisture from entering the cylinder | Choose a profile suited to the environment; a wiper does not replace the pressure-bearing rod seal |
| 6 | Backup ring | Beside an O-ring or other seal in a pressure-loaded groove | PTFE or another specified anti-extrusion material | High resistance to extrusion when correctly selected and installed | PTFE has broad chemical resistance, but the complete seal assembly must be checked for fluid compatibility | Supporting a primary seal where pressure may force it into a clearance gap | Not a stand-alone sealing element; confirm ring direction, clearance, and groove dimensions |
| 7 | Wear ring or guide ring | On the piston or rod assembly inside the cylinder | PTFE composite or other engineered bearing material | Designed to resist guiding loads and reduce metal-to-metal contact | Material compatibility varies; check the product specification for the actual hydraulic fluid | Guiding moving components and helping limit side loading on seals | A guide element, not a fluid seal; size it to the cylinder design and expected load |
| 8 | Bonded sealing washer | Hydraulic ports, plugs, and bolted fluid connections | Metal washer with an elastomer sealing element, commonly NBR | Good for static joints when the mating surfaces and tightening conditions are suitable | Elastomer compatibility depends on the washer compound; NBR is commonly used with mineral oils | Sealing flat-faced connections without relying on a tapered thread | Use the correct inner diameter, outer diameter, thickness, and sealing-face design |
| 9 | V-packing set | Rod or piston in certain serviceable hydraulic cylinders | Fabric-reinforced elastomer or compatible polymer, depending on design | Can provide serviceable sealing in demanding applications when correctly adjusted | Must be matched to the hydraulic fluid and the packing material | Applications designed for an adjustable multi-ring packing arrangement | Requires the correct stack order and gland adjustment; not a direct substitute for a U-cup |
| 10 | FKM O-ring | Static joints or selected hydraulic interfaces requiring a different elastomer compound | Fluoroelastomer (FKM) | Good resistance to heat and many oils when the grade suits the application | Often compatible with petroleum oils; compatibility with particular fluids and low-temperature service must be confirmed | Applications where the specified temperature or fluid requirements favor an FKM compound | Do not assume it is a universal upgrade; check low-temperature flexibility, fluid chemistry, and groove fit |