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OEM U-Cup Seal: Selection, Materials, and RFQ Data
Quick Answer: An OEM U-cup seal is a U-shaped lip seal used as a rod seal or piston seal in hydraulic and pneumatic cylinders. CORASEALS supplies standard and custom U-cup seals in materials such as NBR, FKM, EPDM, HNBR, and polyurethane. For a quotation, send the rod diameter, bore diameter, groove dimensions, fluid, pressure, temperature, speed, and required seal profile.
What Is an OEM U-Cup Seal?
A U-cup seal has a U-shaped cross section. The two lips contact the sliding surface and the groove wall. Hydraulic pressure energizes the lips and increases the sealing force. This profile is widely used on cylinder rods and pistons.
In OEM hydraulic and pneumatic equipment, the U-cup must match the original groove. CORASEALS works from the cylinder drawing, measured housing dimensions, or a sample. Correct groove dimensions matter more than a catalog type code alone.
Rod Seal and Piston Seal Functions
A rod seal U-cup keeps hydraulic fluid inside the cylinder and reduces contamination ingress on the rod side. A piston seal U-cup separates the two pressure chambers inside the cylinder bore.
Most U-cup profiles are single acting. The seal lips normally face the pressure side. In double acting cylinders, two U-cup seals are often used, or a double acting compact profile is selected. Confirm the seal position before ordering.
Common U-Cup Profiles and Type Codes
Buyers often search for U-cup seals by codes such as UN, UHS, or UPH. These codes are useful references, but they are not universal across manufacturers. Groove width, lip height, heel design, and material hardness can differ.
CORASEALS compares the existing seal sample, groove drawing, and dimension list before quoting. Do not replace an OEM U-cup seal by code alone when the cylinder operates at high pressure or high cycle rates.
- UN type U-cup seals: general hydraulic rod and piston applications.
- UHS type U-cup seals: common in hydraulic cylinder sealing positions.
- UPH and similar codes: check lip geometry and backup ring requirements.
Material Selection for OEM U-Cup Seals
Material choice depends on the hydraulic fluid, operating temperature, pressure, speed, and whether the seal is on the rod side or piston side. The table below lists common material options and their typical uses.
| Material | Common Use | Key Limitation |
|---|---|---|
| NBR | Mineral oil hydraulic fluids, water glycol, general pneumatic systems | Limited ozone and weather resistance without protection |
| FKM | Mineral oil and many aggressive fluids, high temperature air and oil | Not suitable for all steam and hot water services depending on the grade |
| EPDM | Water, steam, phosphate ester brake fluids | Not suitable for mineral oil |
| Polyurethane | High pressure hydraulic cylinders, high wear rod and piston positions | Can degrade in hot water or high humidity depending on the grade |
| HNBR | Mineral oil, higher heat than NBR, good abrasion resistance | Check compatibility with polar solvents and some hydraulic fluid additives |
Temperature limits and pressure limits depend on the specific compound and U-cup profile. Send the full operating range. CORASEALS will confirm material compatibility with the supplier data sheet.
Dimensions and Groove Data for OEM U-Cup Seals
For every U-cup seal quote, confirm the seal ID, OD, cross section width, and axial height. Measure the existing seal when possible. Also record the housing groove width, groove depth, rod diameter, and bore diameter. The seal cross section must match the groove, not just the shaft or bore.
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