Bonded Seals
Bonded Seals Overview
Bonded seals, also known as Dowty Seals or Bonded Sealing Washers, are composite sealing elements consisting of a metal washer bonded to an elastomer sealing ring. They are specifically designed to provide reliable, leak-free sealing on threaded ports, bolts, plugs, and hydraulic fittings where conventional copper or aluminum washers may not deliver consistent performance under pressure.By combining the strength of metal with the elasticity of rubber, bonded seals maintain sealing integrity even under pressure fluctuations, vibration, and thermal cycling, making them a preferred choice in hydraulic and fluid power systems.
Why Choose Bonded Seals?
Unlike standard flat washers, bonded seals create both a mechanical support and an elastic sealing barrier. The metal ring prevents excessive compression, while the rubber insert deforms to fill surface irregularities, reducing the risk of leakage.
Key Benefits
- Excellent sealing in high-pressure hydraulic systems
- Prevents leakage around threaded fasteners and ports
- Resistant to vibration and pressure pulsation
- Easy installation with no special groove required
- Reusable in some low-pressure maintenance applications
- Available in metric, BSP, BSPP, and inch sizes
How Bonded Seals Work
When the threaded fitting is tightened, the elastomer insert compresses against the mating surface while the metal washer controls compression. This design prevents over-squeezing of the rubber and creates a reliable seal even if the sealing surfaces have slight imperfections.
Compared with conventional crush washers, bonded seals provide:
- Better sealing consistency
- Improved resistance to pressure spikes
- Longer service life
- Reduced maintenance and retightening requirements
Standard vs. Self-Centering Bonded Seals
Material Options
Choosing the correct elastomer depends on the operating fluid and temperature.
| Elastomer | Recommended Applications |
|---|---|
| NBR (Buna-N) | Hydraulic oil, fuel systems, general industrial equipment |
| FKM (Viton®) | High-temperature oils, fuels, chemicals |
| EPDM | Water, steam, glycol-based fluids |
| Silicone (VMQ) | Low-pressure equipment with wide temperature variation |
| HNBR | Heavy-duty hydraulic and automotive applications |
Metal retainers are commonly manufactured from zinc-plated carbon steel or stainless steel for improved corrosion resistance.
Custom Seal Capabilities
We offer full custom seal solutions tailored to diverse industrial demands. Customize materials, sizes, shapes and hardness to match unique working conditions. Support special temperature, pressure and chemical resistance designs. Meet non-standard installation needs and provide professional OEM sealing products for various equipment applications.
Common Installation Mistakes
Even high-quality bonded seals can fail if installed incorrectly. To maximize sealing performance:
- Select the correct inside diameter for the bolt or fitting.
- Inspect the mating surface for scratches or burrs.
- Tighten according to the manufacturer’s recommended torque.
- Avoid reusing seals that show permanent deformation or rubber damage.
- Choose an elastomer compatible with the operating fluid and temperature.
Proper installation significantly reduces leakage and extends the service life of both the seal and the hydraulic connection.
Bonded Seal Sizes
Bonded seals are available in a wide range of sizes to accommodate both inch and metric fasteners commonly used across various industries. Our size offerings align with standard hardware dimensions to ensure proper fit and reliable sealing performance. The chart below provides detailed measurements to help identify the appropriate bonded seal for your specific application.
| Ref # | Metric | IN | BSP | ID(mm) | OD(mm) | HT (mm) | ID(in) | OD(in) | HT (in) |
|---|---|---|---|---|---|---|---|---|---|
| 603 | M5 | 5.70 | 9.00 | 1.00 | 0.224 | 0.354 | 0.039 | ||
| 606 | M6 | 898 | 6.70 | 10.00 | 1.00 | 0.264 | 0.394 | 0.039 | |
| 607 | M6 | 6.70 | 11.00 | 1.00 | 0.264 | 0.433 | 0.039 | ||
| 612 | M8 | 8.70 | 13.00 | 1.00 | 0.343 | 0.512 | 0.039 | ||
| 613 | M8 | 866 | 8.70 | 14.00 | 1.00 | 0.343 | 0.551 | 0.039 | |
| 820 | 3/8 | 1/8 | 10.37 | 15.88 | 2.00 | 0.408 | 0.625 | 0.079 | |
| 622 | M12 | 12.70 | 18.00 | 1.50 | 0.500 | 0.709 | 0.059 | ||
| 821 | 1/2 | 1/4 | 13.74 | 20.57 | 2.00 | 0.541 | 0.810 | 0.079 | |
| 627 | M14 | 868 | 14.70 | 22.00 | 1.50 | 0.579 | 0.866 | 0.059 | |
| 811 | 5/8 | 869 | 16.51 | 25.40 | 2.00 | 0.650 | 1.000 | 0.079 | |
| 823 | 3/8 | 17.28 | 23.80 | 2.00 | 0.680 | 0.937 | 0.079 | ||
| 632 | M18 | 872 | 18.70 | 26.00 | 1.50 | 0.736 | 1.024 | 0.059 | |
| 633 | M20 | 873 | 20.70 | 28.00 | 1.50 | 0.815 | 1.102 | 0.059 | |
| 825A | 13/16 | 1/2 | 21.54 | 28.58 | 2.50 | 0.848 | 1.125 | 0.098 | |
| 636 | M22 | 874 | 22.70 | 30.00 | 2.00 | 0.894 | 1.181 | 0.079 | |
| 826 | 7/8 | 5/8 | 23.49 | 31.75 | 2.50 | 0.925 | 1.250 | 0.098 | |
| 638 | M24 | 875 | 24.70 | 32.00 | 2.00 | 0.972 | 1.260 | 0.079 | |
| 829 | 1 3/16 | 7/8 | 30.81 | 38.10 | 2.50 | 1.213 | 1.500 | 0.098 | |
| 642 | M30 | 31.00 | 39.00 | 2.00 | 1.220 | 1.535 | 0.079 | ||
| 643 | M33 | 33.70 | 42.00 | 2.00 | 1.327 | 1.654 | 0.079 | ||
| 830A | 1 5/16 | 1 | 33.89 | 42.80 | 3.20 | 1.334 | 1.685 | 0.126 | |
| 832A | 1 5/8 | 1 1/4 | 42.93 | 52.38 | 3.20 | 1.690 | 2.062 | 0.126 | |
| 833A | 1 7/8 | 1 1/2 | 48.44 | 58.60 | 3.20 | 1.907 | 2.307 | 0.126 | |
| 834 | 2 1/8 | 54.89 | 69.85 | 3.20 | 2.161 | 2.750 | 0.126 | ||
| 836A | 2 | 60.58 | 73.03 | 3.20 | 2.385 | 2.875 | 0.126 | ||
| 839 | 2 1/2 | 76.08 | 90.17 | 3.20 | 2.995 | 3.550 | 0.126 |
Why Choose Our Bonded Seals?
- Standard metric and imperial sizes in stock
- NBR, FKM, EPDM, HNBR, and custom material options
- Carbon steel and stainless steel retaining rings available
- Suitable for high-pressure hydraulic and pneumatic systems
- Custom sizes and OEM sealing solutions supported
- Engineering assistance for thread type and material selection
Whether you’re sealing a hydraulic port, pipe plug, or high-pressure fitting, our bonded seals provide a dependable and cost-effective solution for preventing leaks while improving long-term system reliability.