- Bonded Washer Seals are also known as Dowty Seals or Dowty Bonded Washers are high pressure seals typically used in the Mechanical, Hydraulic and Pneumatic applications.
- Bonded Washer Seals were originally designed to replace copper type washers used in high-pressure systems. They consist of a metal washer and an elastomeric ring bonded inside the diameter. The metal washer prevents over-compression and limits deformation of the elastomeric ring.
Characteristics of Bonded Washer Seals
Ideal Pressure Gasket
Reliable sealing at high & low pressure
High & low temperature capability
Reduced bolt torque with no loss of tightening loads
Metal ring prevents over compression of the rubber seal
Properties and Description
Our bonded washers consist of a metal rectangular outer washer with a trapezoid shaped rubber ring bonded to the inner of the ring creating a 1-piece washer with an internal seal. Bonded washers hold a large amount of burst pressure whilst retaining the inner seal shape and limiting deformation resulting in brilliant sealing under high pressures.
EMI Seals & Gaskets Ltd can supply either the Standard style or a Self-Centering style that eliminates the potential of the being slightly seal offset during installation thus simplifying the process. These seals are readily available in Imperial sizes from 1/8 inch to 3 inches. French and German Metric form part of our extensive stock. Imperial and metric size charts can be found at the top of our data sheets below. The inner bonded rubber seal can be manufactured to suit the end user’s application from the following:
| EMI Material Reference | Elastomer Name | Standard Elastomer Hardness Shore A |
|---|---|---|
| 301 | Silicone (VMQ) | 75°±5 SHORE HARDNESS |
| 302 | Fluorosilicone (FVMQ) | 75°±5 SHORE HARDNESS |
| 309 | Nitrile (NBR) | 85°±5 SHORE HARDNESS |
| 309-2 | Hydrogenated Nitrile (HNBR) | 80°±3 SHORE HARDNESS |
| 303 | Fluorocarbon (FKM) | 75°±5 SHORE HARDNESS |
| 306 | EPDM (EPDM) | 85°±5 SHORE HARDNESS |
| Other custom shore hardness’s are available depending on order quantity |
Bonded Washer Thermal Properties
The thermal properties of the bonded washer seals will depend on the specific grade of compound used, please consult compound data sheets or contact a member of our Technical or Relationship Management Teams to discuss a potential project or application in greater detail.
Metal washer can be manufactured to suit the end user’s application from the following:
| METAL | TENSILE STRENGTH MN/m2 (MINIMUM) | SPECIFICATION |
|---|---|---|
| Mild Steel Pressings | 540 | BS 1449 Part 1 CS4 BRH5 |
| Mild Steel Turned | 540 | BS 970 Part 1 EN8 |
| Stainless Steel Pressings | 540 | BS 1449 Part 2 T316 |
| Stainless Steel Turned | 540 | BS 970 Part 1 T303 |
| Stainless Steel Turned | 540 | BS 970 Part 1 T316 |
| Stainless Steel Turned | 540 | BS 970 Part 1 T304 |
Our Bonded Washer Seals are available with a variety of surface finishes:
| SURFACE FINISH | SPECIFICATION |
|---|---|
| Zinc plating | Def. STAN. 03-20 |
| Gold Passivate | Def. STAN. 03-33 |
| Cadmium Plating | Def. STAN. 03-19 |
| Chromic Anodise | Def. STAN. 03-24/2 |
| Sulphuric Anodise | Def. STAN. 03-25/2 |
| Clear Passivate | Fe/Zn-5CIA |
| Zinc/Cobalt and Colour Passivate | ZnCb-921/ST140 |
| Mechanical Zinc Plate | STD.5735,114 Fe/Zn 8 C1 |
| Zinc/Iron and Black Chromate | Fe/Zn - Fe 5 C4 |
| Sherardize 2000 | SHS 1091 |
