What is a Bonded Seal?

What is a Bonded Seal? Hydraulic Thread Seal Washer Explained

A bonded seal, also known as a Dowty seal or thread seal washer, is a metal washer combined with an elastomer sealing ring designed to prevent fluid leakage in high-pressure hydraulic and pneumatic systems.

Bonded seals are widely used in hydraulic fittings, valves, pumps, manifolds, and aerospace fluid systems because they provide reliable sealing under high pressure and vibration conditions.

How Does a Bonded Seal Work?

A bonded seal consists of:

• A metal outer ring for mechanical strength

• A rubber inner sealing lip for leak prevention

When compressed between mating surfaces, the elastomer section creates a tight seal while the metal washer prevents over-compression and deformation.

This design provides:

• High-pressure sealing capability

• Excellent vibration resistance

• Reliable leak prevention

• Long service life

Common Bonded Seal Materials

The rubber sealing element can be manufactured using different elastomer materials depending on operating conditions.

NBR Bonded Seals

Suitable for:

• Hydraulic oil

• General industrial applications

• Pneumatic systems

FKM Bonded Seals

Suitable for:

• High-temperature applications

• Fuel systems

• Aerospace environments

• Aggressive chemicals

EPDM Bonded Seals

Suitable for:

• Water systems

• Steam applications

• Brake fluids

FFKM Bonded Seals

Suitable for:

• Semiconductor processing

• Extreme chemical environments

• Ultra-high purity applications

Common Applications of Bonded Seals

Bonded seals are commonly used in:

• Hydraulic adapters

• BSP and metric fittings

• Hydraulic manifolds

• Pumps and valves

• Aerospace hydraulic systems

• Industrial machinery

• Pneumatic equipment

Because bonded seals combine metal strength and elastomer flexibility, they are often preferred over standard copper washers or flat gaskets in dynamic hydraulic environments.

Parker 750 Series Equivalent Bonded Seals

Many industrial systems use bonded seals equivalent to the Parker 750 Series standard. These sealing washers are designed for high-pressure hydraulic sealing and are available in various inch and metric sizes.

Typical features include:

• High-pressure resistance

• Anti-leak performance

• Vibration durability

• Multiple rubber material options

• Custom dimensions available

Why Bonded Seals are Important in Hydraulic Systems

Hydraulic systems operate under high pressure where even minor leakage can reduce performance and create safety risks. Bonded seals help maintain sealing integrity while improving long-term equipment reliability.

Compared to conventional sealing washers, bonded seals provide:

• Better sealing efficiency

• Reduced maintenance

• Improved durability

• Enhanced pressure resistance

Roman Seal Bonded Seal Manufacturer

Roman Seal Official Website manufactures bonded seals and hydraulic thread seal washers for industrial, automotive, and aerospace applications.

Available products include:

• Parker 750 series equivalent bonded seals

• NAS sealing products

• Hydraulic thread seal washers

• Custom rubber-metal bonded sealing solutions

Materials include:

• NBR

• FKM

• EPDM

• Silicone

• Fluorosilicone

• FFKM

Roman Seal supports both standard and custom sealing requirements for global industrial customers.