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Custom Rod Seals for Hydraulic and Pneumatic Cylinders
Quick Answer: A custom rod seal is a hydraulic or pneumatic sealing element matched to a specific rod diameter, groove dimensions, fluid, pressure, speed, and temperature. The seal stops oil leakage at the rod side and blocks external contamination. CORASEALS can supply a custom rod seal after receiving the rod diameter, bore diameter, groove dimensions, pressure, speed, hydraulic fluid, and seal profile.
A custom rod seal is needed when a standard seal does not match the cylinder rod diameter, groove geometry, or operating conditions. Rod seals work in hydraulic cylinders, pneumatic cylinders, mobile equipment, agricultural machinery, and industrial presses. The rod seal sits in the cylinder head or gland and seals the moving rod surface.
Rod seals differ from piston seals and wiper seals. A piston seal seals the cylinder bore and moves with the piston. A rod seal seals the rod surface and retains oil inside the cylinder. A wiper seal cleans the rod surface at the outside of the cylinder. A complete cylinder head often uses a wiper, a main rod seal, and a buffer seal in series.
Common Custom Rod Seal Profiles
CORASEALS can source different rod seal profiles. The profile must be selected with the groove drawing and operating conditions. Common profiles include:
- U-cup rod seals for general hydraulic cylinders
- Polyurethane rod seals for high wear resistance
- PTFE step seals with an elastomer energizer for low friction
- Compact rod seals for short gland designs
- V-packing sets for adjustable sealing force
- Buffer seals to protect the main rod seal from pressure spikes
Profile codes such as UN, UHS, HBY, and other designations can vary by catalog. CORASEALS checks the cross section, material, and dimensions before quoting a replacement. Do not rely only on a part number or model code.
Material Selection for Custom Rod Seals
The rod seal material must match the hydraulic fluid, temperature, pressure, and rod speed. Common rod seal material options include:
- NBR for general mineral oil service
- HNBR for higher wear and temperature resistance than NBR
- FKM for high-temperature hydraulic oil and synthetic fluid resistance
- Polyurethane for high wear resistance and extrusion resistance
- Filled PTFE for low friction and high-temperature service
EPDM is not normally used for mineral oil hydraulic systems. The final material grade and Shore A hardness depend on the fluid chemistry, temperature range, and duty cycle. CORASEALS reviews the operating data with the material supplier before quoting.
Dimensions and Gland Data Needed
Custom rod seal dimensions usually include the rod diameter, groove diameter, groove width, and gland bore. Some suppliers also require the seal outer diameter and seal height. Both metric and inch measurements are used in hydraulic cylinders. The dimension order must always be confirmed with the drawing.
The rod surface finish, rod hardness, runout, and stroke speed are also important. A rod seal can leak if the rod surface is scored, pitted, or polished incorrectly. The groove clearance must also be checked because a large extrusion gap can damage the seal under pressure.
Common Rod Seal Failure Causes
If a rod seal leaks after installation, the cause may come from the seal, the groove, or the cylinder system. Common failure causes include:
- Incorrect rod diameter or groove clearance
- Rod surface scratches, corrosion, or excessive runout
- Wrong material for the fluid or temperature
- Pressure spikes that extrude the seal lip
- Contaminated hydraulic oil with particles or water
- Installation cuts from sharp threads or missing assembly tools
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