Why Seal Material Selection Matters
In a hydraulic cylinder, the seals are the most maintenance-sensitive component. Seal failure causes external leakage, internal bypass, and ultimately cylinder failure. The correct seal material must withstand the system’s operating pressure, temperature range, and the specific hydraulic fluid being used.
Wuxi Hengshui Machinery sources all seals from German Merkel and American Parker — two of the world’s leading manufacturers of hydraulic sealing systems. We offer three primary seal materials for custom hydraulic cylinders.
NBR (Nitrile Butadiene Rubber)
Best for: General-purpose industrial hydraulics with mineral oil
NBR is the most widely used hydraulic seal material. It offers excellent resistance to petroleum-based hydraulic oils, mineral oils, and many solvent vapours.
- Temperature range: −30°C to +100°C (−22°F to +212°F)
- Pressure resistance: up to 350 bar with appropriate backup rings
- Compatible fluids: Mineral oil (ISO VG 32–68), hydraulic oil (HM, HV type)
- Not recommended for: phosphate ester fluids, ketones, strong acids
NBR is the standard seal material in most Wuxi Hengshui cylinders for metallurgical, press, crane, and construction machinery applications where petroleum-based hydraulic oil is used.
FKM / Viton (Fluoroelastomer)
Best for: High-temperature environments, fire-resistant fluids
FKM (commercially known as Viton) provides superior heat resistance and chemical compatibility compared to NBR. It is the seal of choice for electric furnace cylinders, foundry equipment, and applications near high-temperature zones.
- Temperature range: −20°C to +200°C (−4°F to +392°F)
- Pressure resistance: up to 400 bar
- Compatible fluids: Phosphate ester (HFD), synthetic esters, high-temperature mineral oils
- Not recommended for: ketones, amines, steam at high temperatures
FKM seals are specified for Wuxi Hengshui electric furnace tilting cylinders, die casting machine cylinders, and any application where ambient temperatures exceed 100°C.
Polyurethane (PU)
Best for: High-pressure, high-speed, high-wear dynamic sealing
Polyurethane seals are harder than rubber-based seals and provide outstanding wear resistance and extrusion resistance under high pressures. They are used primarily for rod seals and piston seals in high-dynamic-load applications.
- Temperature range: −40°C to +90°C (−40°F to +194°F)
- Pressure resistance: up to 500 bar (ideal for high-pressure cylinders)
- Key advantages: Excellent abrasion resistance, low friction, good extrusion resistance
- Used for: Rod seals, wiper seals, piston seals in press and forging applications
Summary: Which Seal to Choose?
| Property | NBR | FKM | Polyurethane |
|---|---|---|---|
| Max Temp | 100°C | 200°C | 90°C |
| Max Pressure | 350 bar | 400 bar | 500 bar |
| Wear Resistance | Good | Good | Excellent |
| Mineral Oil | ✓ Excellent | ✓ Good | ✓ Good |
| Cost | Low | High | Medium |
| Typical Use | General industrial | High-temp / furnace | High-pressure press |
When ordering a custom cylinder from Wuxi Hengshui Machinery, specify your hydraulic fluid type, maximum operating temperature, and working pressure. Our engineers will recommend the appropriate seal package from our Merkel and Parker seal inventory. Contact our sales team at sales@wx-hxy.com.