389.2X5.7 NBR 70 ShA O-Ring

What is the 389.2X5.7 NBR 70 ShA O-Ring?

The 389.2X5.7 NBR 70 ShA O-Ring is a precision-engineered metric sealing ring designed to provide reliable static and dynamic sealing in a wide range of industrial applications. Manufactured from NBR (Nitrile Butadiene Rubber) with a hardness of 70 Shore A, it offers excellent sealing performance in systems operating with mineral oils, greases and many hydraulic fluids. With an inside diameter of 389.2 mm and a cross-section of 5.7 mm, this O-ring is suitable for industrial machinery, hydraulic systems, pneumatic equipment and OEM applications where dimensional accuracy and dependable sealing are essential.

Design and Construction

The O-ring is one of the most widely used sealing components in modern engineering due to its simple geometry and outstanding sealing efficiency.

The 389.2X5.7 NBR 70 ShA O-ring features:

• Circular cross-section
• Precision moulded NBR elastomer
• 70 Shore A hardness
• Uniform material structure
• Metric dimensions according to industrial standards

When installed in a correctly designed groove, the elastomer is compressed between mating surfaces, creating a reliable seal that prevents fluid or gas leakage.

Technical Specification

Manufacturer: GRN

Product Type: Metric O-Ring

Part Number: 389.2X5.7 NBR 70 ShA

Material: NBR (Nitrile Butadiene Rubber)

Hardness: 70 Shore A

Inside Diameter: 389.2 mm

Cross Section: 5.7 mm

Profile: Round

Colour: Black

How Does an O-Ring Work?

An O-ring seals by elastic deformation.

During installation, the sealing ring is compressed inside its groove. This compression creates continuous contact pressure between the O-ring and the mating surfaces, preventing the escape of liquids or gases.

As system pressure increases, the pressure itself pushes the elastomer more firmly against the sealing surfaces, improving sealing efficiency. This self-energizing effect is one of the reasons why O-rings remain the preferred sealing solution in hydraulic, pneumatic and industrial equipment.

Why Choose NBR 70 Shore A?

NBR (Nitrile Butadiene Rubber) is one of the most commonly specified elastomers for industrial sealing applications because it provides an excellent balance between mechanical durability, oil resistance and cost-effectiveness.

Key advantages include:

• Good resistance to mineral oils
• Excellent compatibility with greases
• Suitable for petroleum-based fluids
• Good abrasion resistance
• Reliable mechanical properties
• Widely used throughout hydraulic and pneumatic industries

Selecting the Correct O-Ring

Choosing the correct O-ring involves more than matching dimensions.

Engineers should consider:

• Inside diameter
• Cross-section
• Elastomer material
• Hardness
• Operating medium
• Working pressure
• Operating temperature
• Static or dynamic application
• Groove dimensions
• Surface finish of mating components

Correct selection significantly improves sealing reliability and service life.

Installation Recommendations

Proper installation is essential for long-term sealing performance.

Before installation:

• Clean the sealing groove thoroughly.
• Remove sharp edges and burrs.
• Lubricate the O-ring when specified by the equipment manufacturer.
• Avoid twisting the O-ring during installation.
• Inspect all sealing surfaces for damage.

Even minor installation damage may reduce sealing effectiveness and shorten service life.

Common Causes of O-Ring Failure

Most sealing failures are caused by installation or application issues rather than manufacturing defects.

Typical causes include:

• Incorrect material selection
• Incorrect dimensions
• Mechanical damage during installation
• Excessive stretching
• Elastomer ageing
• Contaminated sealing surfaces
• Improper groove design
• Chemical incompatibility

Understanding these failure mechanisms helps improve equipment reliability and reduce maintenance costs.

Industrial Applications

The 389.2X5.7 NBR 70 ShA O-Ring is suitable for industrial equipment designed to use this specific metric size.

Typical applications include:

• Hydraulic systems
• Pneumatic systems
• Industrial pumps
• Hydraulic cylinders
• Pneumatic actuators
• Industrial valves
• Gearboxes
• Manufacturing equipment
• OEM machinery
• MRO maintenance operations

Final application suitability should always be verified according to the equipment manufacturer's technical documentation.

OEM and Industrial Maintenance

O-rings are among the most frequently replaced sealing components during preventive maintenance and equipment servicing.

Replacing worn seals at scheduled maintenance intervals helps:

• prevent fluid leakage,
• reduce unexpected machine downtime,
• improve equipment reliability,
• extend component service life,
• support predictive maintenance strategies.

For OEM manufacturers and maintenance engineers, selecting the correct material and dimensions is essential for long-term sealing performance.

Why Engineers Choose NBR 70 ShA O-Rings

• Industry-standard metric dimensions
• NBR material suitable for oil and grease applications
• 70 Shore A hardness for versatile industrial use
• Reliable static and dynamic sealing
• Simple and cost-effective sealing solution
• Easy installation and replacement
• Widely used in OEM equipment
• Trusted for hydraulic, pneumatic and industrial machinery

Frequently Asked Questions (FAQ)

What does 70 Shore A mean?

It specifies the hardness of the NBR elastomer according to the Shore A hardness scale.

Can this O-ring be used with mineral oils?

Yes. NBR is widely used in systems operating with mineral oils and lubricating greases.

Is this O-ring suitable for dynamic sealing?

Yes, provided the application, groove design and operating conditions are appropriate.

How do I select the correct O-ring size?

Selection should be based on the inside diameter, cross-section and groove dimensions specified by the equipment manufacturer.

Can I replace this O-ring with a similar size?

No. Even small dimensional differences may reduce sealing efficiency and lead to leakage.

Where are NBR O-rings commonly used?

They are widely used in hydraulic systems, pneumatic equipment, pumps, valves, gearboxes and general industrial machinery.