O-ring Static joints, plugs, and some low-motion sealing points | NBR (nitrile rubber) | About -30°C to +100°C | Specify inside diameter (ID) × cross-section (CS). Example measurement: 20 × 2.5 mm. Confirm the actual groove size and required squeeze before ordering. | Good general-purpose resistance to mineral hydraulic oils and cost-effective. Less suitable for prolonged exposure to ozone, sunlight, or some chemicals. | Check for a round, even cross-section, smooth surface, correct ID and CS, and no cuts, cracks, flat spots, or molding flash. |
Piston seal / U-cup Inside the lift cylinder | Polyurethane (PU) | Often about -30°C to +100°C; compound-specific | Measure cylinder bore, seal groove diameter, groove width, and seal height. Match the original profile; dimensions are not interchangeable based on bore alone. | Typically offers good wear and extrusion resistance in hydraulic service. Compatibility and performance depend on hardness, profile, pressure, and clearances. | Look for a consistent lip profile, clean molded edges, no nicks or bubbles, and documented material and hardness specifications. |
Rod seal Where the piston rod exits the cylinder | PU or NBR, selected for the design and fluid | Commonly about -30°C to +100°C; verify the compound rating | Check rod diameter, housing bore, gland width, seal height, and lip orientation. Measure the old seal and gland where possible. | Designed to retain hydraulic fluid around a moving rod. Incorrect fit, damaged rod finish, or excessive clearance can cause leakage or rapid wear. | Inspect the sealing lip for uniformity and damage. Check the rod for scratches, corrosion, and burrs that could cut the new seal. |
Wiper / dust seal At the cylinder opening | NBR or PU | Often about -30°C to +100°C; depends on material and exposure | Measure rod diameter, housing bore, groove width, and overall profile. Ensure the wiping lip faces outward to exclude dirt. | Helps keep dust and debris out but is not normally a substitute for a pressure-retaining rod seal. | Check the lip for an even edge and flexibility. Reject parts with splits, permanent deformation, or an incorrect press-fit profile. |
Backup ring Used beside an O-ring in some designs | PTFE or a compatible thermoplastic | PTFE can cover a broad temperature range; the complete assembly sets the practical limit | Match the O-ring groove, ring thickness, diameter, and split style. Confirm the ring fits the specified groove without gaps that allow extrusion. | Supports the primary seal against extrusion in suitable designs. It is generally a support component, not a standalone replacement for the O-ring. | Check for flat, clean faces, correct thickness, and no chips or distortion. Confirm compatibility with the fluid and the original seal arrangement. |
Special-fluid or high-temperature seal Only where service conditions require it | FKM (fluoroelastomer), subject to fluid compatibility | Often about -20°C to +200°C; exact limits depend on compound | Use the same dimensional checks as the corresponding O-ring or shaped seal. Match the exact cross-section, ID, profile, and gland dimensions. | Can suit some higher-temperature or chemical environments, but may cost more and is not automatically the best choice for standard mineral-oil service. | Request the compound specification and fluid-compatibility confirmation. Verify dimensions and inspect for cracks, surface defects, or hardening. |