John Crane mechanical seal portfolio around four intersecting axes: secondary sealing member, arrangement, mounting style, and lubrication principle. For engineers specifying spares or planning MRO budgets, the useful view is not "a list of 200 model numbers" but a matrix that maps duty severity to a seal family—then, where applicable, to a cost-effective interchangeable alternative such as those produced by NINGBO MIAOYU MACHINERY TECHNOLOGY CO., LTD.

1. By Secondary Sealing Member

The oldest dividing line in John Crane mechanical seal design is what compensates for shaft axial movement.

• Elastomer bellows seals – e.g., Type 109, Type 502, Type 58U/58B. Rubber or PTFE bellows act as both spring and secondary seal. Simple, low-cost, suited to water, light hydrocarbons, and general-service pumps where temperature and chemistry stay moderate.

• O-ring pusher seals – e.g., Type 1648, Type 4610, 5600 Series (5610/5620). A separate spring (often wave or multi-spring) pushes the seal face while an O-ring provides the dynamic secondary seal. This is the workhorse for refinery and chemical duties and the basis of most API 682 Category 1 cartridge seals.

• Metal bellows seals – e.g., 5600 Series metal-bellows heads, Type 1604HTC, Type 3604HTC, Type 2800MB. A welded metal bellows replaces elastomers entirely, removing the dynamic O-ring. Preferred for high temperature, cryogenic service, or fluids that swell or attack elastomers.

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2. By Arrangement (Single, Tandem, Double)

API 682 classifies seals into Arrangement 1 (single), 2 (tandem/unpressurized dual), and 3 (double/pressurized dual). John Crane covers all three.

• Single seals – Type 5610 (O-ring pusher), Type 5615 (metal bellows), Type 4610. One sealing interface; used when the process fluid is non-hazardous or can tolerate minor vapor leakage to atmosphere.

• Tandem (unpressurized dual) seals – Type 5620, Type 2648. Two seal sets in series with a buffer fluid at lower pressure than the process. The outboard seal contains any inboard leakage; common in light-hydrocarbon and low-emission refinery pumps.

• Double (pressurized dual) seals – Type 3648, Type 5620D, Type 3604. Barrier fluid is pressurized above process pressure so zero process fluid reaches atmosphere. Mandatory for toxic, volatile, or oxygen-mixing services.

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3. By Mounting Style

• Component (shaft-mounted) seals – Traditional Type 109, Type 59B/U, Type 58U. Assembled on-site part by part. Still common in legacy equipment and DIN-based European installs.

• Cartridge seals – Pre-assembled units with sleeve, gland, spring, and faces set to correct compression. The 5600 Series (5610/5615/5620) is John Crane's "universal cartridge" concept: one gland footprint fits ANSI B73.1M, ISO 3069, and DIN 24960 chambers, with interchangeable elastomer/metal-bellows heads. API 682 effectively mandates cartridge design for new refinery pumps.

• Split seals – Type 3740, 3740D, 3740XL, 37FS, 75FS. Halved design clamps around the shaft without dismantling the pump or agitator. Used on large water/wastewater rolls, paper-machine drives, and top-entry mixers where tear-down cost is prohibitive.

• Vessel / agitator seals – Type 32, 32D, 32i, 5280/5281/5282 (hygienic). Dry-running outside-mounted mixer seals or modular hygienic cartridges for pharma/food glass-lined vessels.

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4. By Lubrication Principle

• Liquid-film (wet) seals – The majority of O-ring pusher and bellows pumps seals rely on a thin process or flush liquid film between faces.

• Gas-lubricated non-contacting seals – Type 2800E, 2800MB, 2874, 2874HTC. Spiral-groove lift technology keeps faces apart on a gas film (nitrogen or instrument air), giving near-zero friction, no seal liquid, and 0.0 fugitive emissions. Type 2800E targets small-bore pumps (25–100 mm) at up to 16 bar(g) and 260 °C; 2874HTC extends this to high-temperature refinery service.

• Dry gas seals (DGS) – For centrifugal compressors and turbomachinery, John Crane supplies spiral-groove dry gas seals with Laser Groove Technology, now the default for most new compressor trains.

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5. By Duty Severity

• General purpose – Elastomer bellows and O-ring pusher seals for water, HVAC, light solvents.

• API / refinery grade – 5600 Series, 1648/2648/3648, 1604/3604 HTC metal bellows, all API 682 qualified.

• Slurry / abrasive – Type 5840 (cost-effective single cartridge), Type 5860 (heavy-duty single/double), Type 5870 (flushless).

• Extreme temp / corrosive – Metal bellows with SiC vs. Diamond® faces; titanium bellows on 2800E for chlorine/ferric chloride.

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Why the Taxonomy Matters

Specifying "a John Crane seal" is never enough. A maintenance planner who confuses a Type 5610 (single, O-ring, wet) with a Type 5620 (dual, tandem) or a Type 2800E (gas-lubricated, non-contacting) will either overspend or create a safety gap. The practical path is:

1. Define arrangement from fluid hazard and API class.

2. Pick secondary member from temperature/chemistry (elastomer → O-ring → metal bellows).

3. Choose mounting from shaft access (cartridge vs. split vs. component).

4. Select face tech (Diamond®, spiral groove, wet/dry head) from lubrication reality.

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6. Where NINGBO MIAOYU Enters the Picture

Miaoyu (Ningbo, est. 2015; 1,500 m² base; ISO 9001; OEM/ODM; exports to 50+ countries incl. US/DE/FR/IN/IR/BR) does not manufacture "John Crane" branded seals, but its catalog is built around the same structural families and is positioned for brand-compatible MRO replacement:

Miaoyu's published edge case—Model 606 as a JC Type 606 replacement for hot oil/asphalt up to 425 °C, all-graphite secondary—shows the overlap zone: same duty map, factory-direct price, 24-hour engineering quote, reverse engineering from sample or drawing.

John Crane's modular logic—especially the 5600 Series where one gland plate serves elastomer, O-ring, and metal-bellows heads—exists precisely so plants can collapse seal inventory while staying covered across duties.