What is a bonded washer (Dowty seal), and how does it seal threaded connectors?

A bonded washer (also called a Dowty seal or Dowty washer) is a metal outer ring with an inner rubber ring that acts as the gasket. The metal provides structural support and prevents over-compression of the elastomer; the rubber seals against the mating faces, absorbs vibration and reduces the risk of loosening under dynamic movement on bolted or screwed fluid connections.

When should bonded washers be specified instead of plain metallic or fibre washers?

Specify bonded washers for high-pressure hydraulic and pneumatic pipework connections, and for other fluid-transfer duties (fuel, hydraulic, pneumatic, HVAC / cooling) where a metal-backed elastomer seal is needed to maintain joint integrity under pressure, temperature and media attack that plain metallic or fibre washers cannot sustain. Suitability still depends on the metal and elastomer selected.

How do you select metal and elastomer grades for a bonded washer?

Specify both the metal washer and the rubber insert against operating media, temperature and environment. Common metals are mild steel, stainless steel and aluminium bronze (other grades on request). Elastomer inserts are available in NBR, HNBR, FKM and EPDM; prefer low-compression-set grades where vibration or heat cycling would otherwise drive interim re-tightening.

How should temperature limits be specified for James Walker bonded washers?

Do not treat the published envelope as simultaneous with every pressure and media combination. The datasheet / product page state a maximum operating temperature of +200Â°C (+392Â°F) and a minimum of âˆ’40Â°C (âˆ’40Â°F), with performance dependent on materials of construction; consult James Walker if duty falls outside those figures.

When should a self-centring bonded washer be specified instead of the standard design?

Specify the self-centring variant where assembly access or vision is limited, or where correct alignment must be assured during fit: the rubber element is designed to self-centre, simplifying installation and reducing the risk of trapping or damaging the sealing element. Use the standard circular configuration where those assembly constraints do not apply.

How should bonded washer size be specified (BSP, metric and regional standards)?

Specify thread system and size first. Standard coverage includes BSP from 1/8" to 2 1/2" and metric from M8 to M24, with German, French and CETOP (ISO 1179) sizing options also available. For self-centring parts, use the datasheet size reference and DÃ˜ / dÃ˜ / thickness (S) dimensions against the named thread.

How should torque, interim re-tightening and reuse be framed for bonded washers?

The metal ring limits over-compression of the elastomer; specify a low-compression-set rubber insert where vibration or heat cycling would otherwise require interim tightening. The product page and datasheet position low-compression-set grades as providing a consistent seal that does not need interim tightening under those conditions. Confirm assembly torque and any reassembly policy with JW applications engineering rather than assuming a single portfolio-wide figure.

How are custom shapes and non-standard bonded washers covered?

The usual presentation is circular, but the same metal-to-rubber bonded concept can be produced in customised shapes for specific applications. Metal and elastomer grades can also be varied beyond the common mild steel / stainless / aluminium bronze and NBR / HNBR / FKM / EPDM options to meet customer requirements.

What should be specified when ordering or enquirying for James Walker bonded washers?

Provide thread standard and size (BSP, metric, or German / French / CETOP ISO 1179), design (standard or self-centring), metal grade, elastomer family/compound, media, continuous and minimum temperature, system pressure, and any custom geometry or certification needs. Use the bonded washers datasheet for size references and published temperature bounds, then confirm the combination with JW applications engineering.

How should sealing performance under vibration and heat cycling be specified?

Specify a bonded washer with a low-compression-set elastomer insert so the rubber maintains a consistent seal without interim tightening when the joint sees vibration or heat cycling; rely on the metal ring to prevent over-compression and on the elastomer to seal and absorb vibration at the mating faces.

What is a bonded washer (Dowty seal), and how does it seal threaded connectors?

A bonded washer (also called a Dowty seal or Dowty washer) is a metal outer ring with an inner rubber ring that acts as the gasket. The metal provides structural support and prevents over-compression of the elastomer; the rubber seals against the mating faces, absorbs vibration and reduces the risk of loosening under dynamic movement on bolted or screwed fluid connections.

When should bonded washers be specified instead of plain metallic or fibre washers?

Specify bonded washers for high-pressure hydraulic and pneumatic pipework connections, and for other fluid-transfer duties (fuel, hydraulic, pneumatic, HVAC / cooling) where a metal-backed elastomer seal is needed to maintain joint integrity under pressure, temperature and media attack that plain metallic or fibre washers cannot sustain. Suitability still depends on the metal and elastomer selected.

How do you select metal and elastomer grades for a bonded washer?

Specify both the metal washer and the rubber insert against operating media, temperature and environment. Common metals are mild steel, stainless steel and aluminium bronze (other grades on request). Elastomer inserts are available in NBR, HNBR, FKM and EPDM; prefer low-compression-set grades where vibration or heat cycling would otherwise drive interim re-tightening.

How should temperature limits be specified for James Walker bonded washers?

Do not treat the published envelope as simultaneous with every pressure and media combination. The datasheet / product page state a maximum operating temperature of +200Â°C (+392Â°F) and a minimum of âˆ’40Â°C (âˆ’40Â°F), with performance dependent on materials of construction; consult James Walker if duty falls outside those figures.

When should a self-centring bonded washer be specified instead of the standard design?

Specify the self-centring variant where assembly access or vision is limited, or where correct alignment must be assured during fit: the rubber element is designed to self-centre, simplifying installation and reducing the risk of trapping or damaging the sealing element. Use the standard circular configuration where those assembly constraints do not apply.

How should bonded washer size be specified (BSP, metric and regional standards)?

Specify thread system and size first. Standard coverage includes BSP from 1/8" to 2 1/2" and metric from M8 to M24, with German, French and CETOP (ISO 1179) sizing options also available. For self-centring parts, use the datasheet size reference and DÃ˜ / dÃ˜ / thickness (S) dimensions against the named thread.

How should torque, interim re-tightening and reuse be framed for bonded washers?

The metal ring limits over-compression of the elastomer; specify a low-compression-set rubber insert where vibration or heat cycling would otherwise require interim tightening. The product page and datasheet position low-compression-set grades as providing a consistent seal that does not need interim tightening under those conditions. Confirm assembly torque and any reassembly policy with JW applications engineering rather than assuming a single portfolio-wide figure.

How are custom shapes and non-standard bonded washers covered?

The usual presentation is circular, but the same metal-to-rubber bonded concept can be produced in customised shapes for specific applications. Metal and elastomer grades can also be varied beyond the common mild steel / stainless / aluminium bronze and NBR / HNBR / FKM / EPDM options to meet customer requirements.

What should be specified when ordering or enquirying for James Walker bonded washers?

Provide thread standard and size (BSP, metric, or German / French / CETOP ISO 1179), design (standard or self-centring), metal grade, elastomer family/compound, media, continuous and minimum temperature, system pressure, and any custom geometry or certification needs. Use the bonded washers datasheet for size references and published temperature bounds, then confirm the combination with JW applications engineering.

How should sealing performance under vibration and heat cycling be specified?

Specify a bonded washer with a low-compression-set elastomer insert so the rubber maintains a consistent seal without interim tightening when the joint sees vibration or heat cycling; rely on the metal ring to prevent over-compression and on the elastomer to seal and absorb vibration at the mating faces.

Website banners 1440 570 silver washer a

Bonded washers

Metal to rubber bonded washers, also known as Dowty seals

What are bonded washers?

Designed for use as connector seals in hydraulic equipment, bonded seals (commonly known as Dowty Seals or Dowty Washers) are used across a broad range of applications including fluid systems in power generation, aviation and defence and general industrial applications.

Downloads

Bonded washers datasheet

Download

Typical applications
Bonded washers are suitable for the majority of fluid transfer applications, including fuel, hydraulic, pneumatic and HVAC / cooling systems. Suitability for specific applications is dependent on the materials selected.

Materials of construction
Both the metal and rubber materials can be specified in a variety of options to match the operating conditions of the application.

The metal washer is commonly available in mild steel, stainless steel, and aluminium bronze, but can also be produced in other material grades to meet specific customer requirements.

The rubber sealing insert is available in nitrile (NBR), hydrogenated nitrile (HNBR), fluoroelastomer (FKM) and ethylene propylene diene (EPDM) elastomers. Rubbers with low compression set are preferable to provide a consistent, effective seal requiring no interim tightening even when subject to vibration or heat cycling.

Performance

Max temperature +200°C (+392°F)
Min temperature -40°C (-40°F)
Performance parameters are dependent on materials of construction – contact James Walker applications engineering team if performance outside the stated parameters is required.

Sizes

BSP - 1/8" to 2 1/2 "
Metric - M8 to M24
German, French and CETOP (ISO1179) sizing options also available

Expert to Expert

Want to discuss your project, engineering or materials challenge expert to expert? Simply provide us with your contact details and a little information about the application you are working on, and one of our experts will contact you as soon as possible.

At James Walker we work together with our customers to engineer a safer, more sustainable world.

Expert sealing and joint integrity solutions for every industry, designed through face-to-face collaboration.

Elast-O-Pure EP75 comes out ahead in top 5 hygienic gasket test over 1,000 SIP cycles - full report now available.

Our experts share their knowledge on issues concerning sealing, bolting and best practices for installation and maintenance.

Do you have a project, engineering or materials challenge? Provide us with your details and one of our experts will contact you to discuss it.

Bonded washers

What are bonded washers?

Bonded washers datasheet

Expert to Expert