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UPH Hydraulic U Seal NBR FKM PU Piston Rod Seal for Construction Machinery Cylinder
Category：U-Cup Seal
Temperature：-30℃ ~ +120℃
Material：NBR
Color：Black
Hardness：70~90 Shore A
Product description：
UPH seal is a heavy-duty U-type reciprocating hydraulic seal originated from NOK standard, serving as universal main seal for piston and piston rod. It features thick U-lip structure, excellent low-pressure sealing performance and automatic tight fitting under high pressure. Back-to-back installation realizes bidirectional sealing, widely used for engineering machinery hydraulic cylinders.
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1. Product Overview
UPH seal is a U-shaped reciprocating hydraulic seal originally developed by NOK Japan. It is a dual-purpose U-seal for piston and piston rod with a thick U-lip structure for one-way sealing. Back-to-back installation enables two-way sealing. Widely adopted as the main hydraulic cylinder seal for construction machinery, categorized as an enhanced version of UN U-seal.
Model Marking Rule
Format: UPH Inner Diameter (ID) × Outer Diameter (OD) × Height (H)
Example: UPH25 means ID 25mm customized outer diameter and fixed sectional height.
2. Main Materials, Hardness & Color
| Material | Abbreviation | Hardness | Standard Color | Suitable Working Conditions |
|---|---|---|---|---|
| Nitrile Butadiene Rubber | NBR | 85~90 Shore A | Black | Conventional hydraulic oil, engine oil, water-glycol emulsion, cost-effective general model |
| Fluoroelastomer | FKM / Viton | 85~90 Shore A | Brown / Coffee | High temperature, fire-resistant phosphate ester oil, hot oil, acid & alkali chemical resistance |
| Polyurethane | PU | 93±2 Shore A | Green / Black | Super wear resistance, heavy load, high-pressure hydraulic cylinders |
3. Technical Performance Parameters
Working Limits
- Working Pressure
- Single seal without back-up ring: ≤25MPa (250bar)
- Equipped with PTFE / PA anti-extrusion back-up ring: Max 32~40MPa (320~400bar) Back-up ring is mandatory for high-pressure working conditions.
- Reciprocating Linear Speed: ≤0.5m/s, best for low-speed cylinders
- Operating Temperature Range
- NBR: -35℃ ~ +110℃
- FKM: -20℃ ~ +150℃
- PU: -40℃ ~ +120℃
- Compatible Media
- NBR: Mineral hydraulic oil, grease, water-oil emulsion, water-glycol
- FKM: High-temperature hydraulic oil, phosphate ester fire-resistant oil, diesel fuel, weak acid & weak alkali liquid
- PU: Wear-resistant hydraulic oil, clean water, low-pressure water hydraulic system
Product Advantages
- Universal for shaft and bore installation, applicable to both piston rod (shaft seal) and piston (bore seal), easy stock preparation.
- Thick U-lip design provides excellent low-pressure sealing performance; lip fits tightly under elevated pressure.
- Low compression set, excellent tear resistance, adapts to slight piston rod eccentricity and sudden load fluctuation.
- Integrated structure for easy installation without complicated assembly.
- Lower friction at startup compared with double-lip oil seals, reducing cylinder starting resistance.
Product Disadvantages
Not applicable for ultra-high pressure over 25MPa. The seal root is prone to extrusion damage under large clearance without back-up ring. Designed only for reciprocating motion, forbidden for rotary sealing scenarios.
4. Installation Instructions
- Single-way sealing (standard hydraulic cylinder): Single UPH seal installed with sealing lip facing the pressure oil chamber.
- Two-way pressure-resistant cylinder: Two UPH seals installed back-to-back for bidirectional pressure sealing.
- High-pressure installation suggestion: Install anti-extrusion back-up ring on one side of the groove. Chamfer the groove edge to R0.3~R0.5 and remove all burrs to prevent lip cutting during assembly.
5. Application Fields
Mainly used for heavy-duty hydraulic cylinders of construction machinery: excavators, loaders, bulldozers, dump trucks, forklifts, cranes, aerial work platforms, mining trucks.
Also applicable for agricultural machinery, forestry equipment, injection molding machine cylinders, industrial heavy-duty hydraulic cylinders, aftermarket replacement seals compatible with original NOK UPH seals.
6. Model Comparison for Selection
- UPH: Thick-section U-seal for heavy-load & high-pressure main cylinder sealing
- USH: Narrow-section U-seal for compact cylinders and secondary sealing inside dust seals
- UN: General-purpose U-seal with thin cross-section for light-duty cylinders; UPH is the reinforced heavy-duty upgraded version of UN seal
7. Storage & Usage Notes
- Storage environment: 5℃~25℃, avoid direct sunlight, ozone, heat sources and long-term oil soaking.
- Restore to room temperature after cold storage before assembly to avoid cracking caused by hardened rubber.
- Strictly follow standard groove clearance to avoid seal failure caused by excessive clearance extrusion.
8. Common Standard Sizes
UPH6.3×16.3×7.5, UPH6.3×16.3×8, UPH11.2×21.2×7.5, UPH12×25×8, UPH25, UPH30, UPH40. Custom oversized seals up to 1600mm inner diameter are available for large hydraulic cylinders.
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