Oct . 18, 2025 13:00 Back to list

Bonded Seal Kit – Leak-Proof, High-Pressure, OEM Sizes

Bonded Seals (Dowty Seals): The Quiet Fix Behind Leak-Free Hydraulics

If you work around hydraulics, you already know this: the humble bonded seal kit is where many “mystery leaks” go to die. In fact, it’s one of those components that rarely gets a headline—until it fails. Over the past decade, I’ve watched bonded seals (some still call them Dowty seals) replace copper washers almost everywhere high pressure and repeatability are non‑negotiable.

What They Are, Why They Work

A bonded seal pairs a metal washer (steel or stainless) with a molded elastomer lip (NBR, HNBR, FKM). The metal ring prevents over‑compression; the elastomer flows to fill micro-gaps around threads/ports. The geometry is deceptively simple: a trapezoidal rubber profile bonded to the inner diameter to keep pressure where it belongs.

Quick Spec Sheet (typical, real use may vary)

Metal Washer	Carbon steel (zinc plated) or 304/316 stainless
Elastomers	NBR 70–90A, HNBR ≈80A, FKM 75–90A
Sizes	M5–M64; BSP 1/8″–2″; UN/ISO 6149 ports
Pressure (static)	Up to ≈60 MPa (8700 psi) with steel/NBR; consult for dynamic
Temp range	NBR: −30~+100°C; HNBR: −25~+150°C; FKM: −15~+200°C
Standards touchpoints	ISO 6149 (ports), DIN 7603 (sealing rings), ISO 815/48-4 (rubber tests)

How They’re Made (shop-floor reality)

Materials: stamped steel or 316 SS washers; NBR/HNBR/FKM compounds per ASTM D2000 class.
Prep: degrease → grit blast → primer/adhesive (rubber-to-metal bonding).
Molding: transfer/compression mold the elastomer; vulcanize; post‑cure for FKM.
Finishing: plating (e.g., zinc) and passivation; lot marking and bagging.
Testing: hardness ISO 48‑4; compression set ISO 815‑1; adhesion ASTM D429; salt‑spray ASTM B117 for plated steel; hydrostatic proof 1.5× rating; cleanliness ISO 16232.
Typical service life: 5–10 years in static joints (clean oil, proper torque). Field results vary.

Where They Shine

Hydraulic pumps and manifolds, banjo bolts on fuel lines, gearboxes, test benches, and subsea connectors. Many customers say installation is “fit and forget” when torque specs are respected and surfaces are clean.

Industry Trends I’m Seeing

Shift to stainless 316 + FKM for aggressive media and higher temps.
Color-coded elastomers for line-side identification (saves rework, surprisingly).
Traceability: QR-coded pouches, PPAP for OEMs, and REACH/RoHS compliance.

Vendor Snapshot (what buyers compare)

Vendor	Materials/Compounds	Certs/Docs	Lead Time	Notes
YJM Seal (OEM)	Steel/304/316 + NBR/HNBR/FKM	COC, material traceability; ISO 9001 on request	≈2–4 weeks	Custom sizes, color ID, PPAP support
Regional Distributor	Common sizes, NBR focus	Basic COC	Stock to 1 week	Fast for MRO, limited customization
Generic Import	Varies; mixed plating	Sparse	Uncertain	Verify rubber hardness and bond

Customization Playbook

Custom IDs/ODs, stainless 316 for corrosion, FKM for hot oils, HNBR for bio‑diesel, low-temp NBR for −40°C, laser-etched lot codes, and kit bagging. If you need a bonded seal kit tailored for PPAP or special fluids, ask for compound data sheets and compression-set curves.

Field Notes (mini case studies)

Excavator OEM: swapped copper washers for steel/NBR 90A bonded seals on banjo bolts; leak returns dropped to 0 in 12 months across ≈4,000 units (torque audit helped).
Food-grade pump skid: 316 SS + FKM seals resisted CIP chemicals; maintenance interval extended from quarterly to annual checks.

Procurement Details

Origin: JULU INDUSTRY AREA, XINGTAI CITY, HEBEI PROVINCE, CHINA 055250. For a production bonded seal kit, specify port/thread standard, media, temperature, pressure, and torque method. Request ISO/ASTM test data and plating spec—small details, big impact.

Testing Snapshot (example data)

Hydrostatic hold: 60 MPa, 1 hour, no visible leakage (sample plate test).
Compression set (ISO 815‑1, NBR 90A, 24h/100°C): ≈18%.
Adhesion (ASTM D429, Method B): rubber-tearing bond observed.

Authoritative citations:

ISO 6149-1: Connections for fluid power and general use — Ports and stud ends. https://www.iso.org/standard/69710.html
DIN 7603: Sealing washers — Requirements and dimensions. https://www.beuth.de/en/standard/din-7603/130818116
ISO 815-1: Rubber, vulcanized — Determination of compression set. https://www.iso.org/standard/71679.html
ISO 48-4: Rubber — Determination of hardness (Shore). https://www.iso.org/standard/76163.html
ASTM D2000: Standard Classification System for Rubber Products. https://www.astm.org/d2000
ASTM D429: Rubber—Adhesion to rigid substrates. https://www.astm.org/d0429
ASTM B117: Standard Practice for Salt Spray. https://www.astm.org/b0117

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