Metal Bellow Double Cartridge Mechanical Seal (Inboard Bellow & Outboard Multi-Spring Design)

Product Overview; 

The BD740 is a heavy‑duty metal bellows double cartridge mechanical seal designed for demanding and hazardous services where process containment, reliability and operational safety are critical. This dual‑seal cartridge provides a compact, fully pre‑assembled solution that combines two complementary sealing technologies within one unit, simplifying installation and improving consistency across critical rotating equipment. 

 

The inboard seal employs a rotating metal bellows assembly that delivers excellent thermal stability and chemical resistance in high‑temperature, high‑pressure and aggressive media. By eliminating dynamic elastomers on the primary seal, the BD740 avoids O‑ring hardening, cracking and hang‑up, making it highly suitable for hot oil, thermic fluids, hydrocarbons and other process fluids that typically degrade conventional pusher‑type seals. 

 

The outboard seal utilises a multi‑spring pusher design, providing uniform face loading, superior pressure‑handling capability and good axial flexibility across a range of barrier or buffer fluid conditions. This secondary seal acts as a containment barrier and supports operation with pressurised (Plan 53) or unpressurised (Plan 52) dual‑seal systems in accordance with API 682 guidelines for hazardous and environmentally sensitive services. 

 

Cartridge‑mounted construction with factory preset working length ensures accurate alignment, simplified installation and reduced commissioning errors in refinery, petrochemical, LPG, power‑generation and chemical‑processing applications. The hydraulically balanced dual‑seal geometry minimises face loading and heat generation, delivering stable performance under fluctuating pressures and temperatures typical of high‑energy process pumps and other critical rotating machinery. 

 

Technical Features; 

• Bi‑directional operation, independent of shaft rotation direction, enables flexible integration with different pump designs and rotation configurations. 

• Available in metric and inch shaft sizes, designed for compatibility with API, ANSI and ISO pump standards and auxiliary piping plans, enabling seamless integration into new or existing systems. 

• Outboard multi‑spring secondary seal improves pressure stability and barrier/buffer fluid management, supporting API 682 dual‑seal piping plans such as unpressurised (Plan 52) and pressurised (Plan 53) variants. 

• Quick installation and easy removal of the cartridge unit support fast change‑out and maximise plant uptime, with bi‑directional operation independent of shaft rotation direction for flexible equipment integration. 

• Integrated cooling, flushing and quench connections provide built‑in interfaces for barrier/buffer and cooling circuits, improving heat dissipation, face cleanliness and emission control in high‑temperature and environmentally critical services. 

• Hydraulically balanced seal faces on both stages reduce face loading and heat generation, extending seal life and maintaining reliable performance in thermic‑fluid, hot‑oil and refinery process pump applications under pressure transients and temperature cycling. 

• Double cartridge configuration with primary metal bellows and secondary multi‑spring pusher seals provides enhanced leakage containment and high reliability safety for hazardous, toxic, flammable, volatile hydrocarbon services and environmentally critical fluids. 

• Factory‑assembled and pressure‑tested double cartridge construction ensures precise alignment, leak‑free performance and compliance with stringent industry standards, while minimising installation errors and downtime and shortens turnaround time during maintenance. 

• Inboard rotating metal bellows design eliminates dynamic elastomer limitations in high‑temperature service, offering superior thermal stability, heat‑related failures, resistance to coking and excellent compatibility with aggressive hydrocarbons and thermic‑fluid media. 

 

 

Service Overview; 

Parameter	Value
Equipment	Process Pumps, API Pumps, Hot Oil Pumps, Refinery Pumps, Boiler Feed & Hydrocarbon Transfer Pumps
Fluid	Hydrocarbons, Thermic Fluid, Hot Oil, LPG, Fatty Acid, Hazardous Chemicals, Volatile Liquids
Service Nature	High Temperature, Hazardous, Corrosive, Flammable & Toxic Fluid Handling
Operating Mode	Continuous Duty / High Reliability Process Service

 

 

 

 

Specifications; 

Item	Min	Max	Typical / Notes
Shaft Size	20 mm (0.750”)	200 mm (8.000”)	Larger sizes available on request
Pressure	Vacuum	25 bar (362 psi)	Depending on seal arrangement & flush plan
Temperature	-40°C (-40°F)	+400°C (+752°F)	Metal bellows optimized for elevated temperature
Speed	—	3600 RPM	Higher speeds available upon application review

 

Materials; 

Component	Standard Material	Optional Material	Comment
Seal Faces	Carbon / Silicon Carbide	Tungsten Carbide / Reaction Bonded SiC	Based on fluid lubricity & abrasiveness
Metal Bellows	SS 316L / AM350	Hastelloy C276 / Inconel Alloy	High-temperature corrosion resistance
Secondary Seal Elastomers	Graphite / Flexible Graphite	FKM / PTFE / Encapsulated FEP	Outboard arrangement dependent
Hardware	SS 316 / SS 316L	Duplex SS / Hastelloy / Titanium	For corrosive or aggressive services

 

Applications; 

• Petrochemical process pumps 

• LPG handling and storage systems 

• Refinery hydrocarbon transfer systems 

• API process pumps in oil & gas facilities 

• Power plant auxiliary and thermal systems 

• Hot oil and thermic fluid circulation pumps 

• Hazardous and volatile chemical processing 

• Fatty acid and specialty chemical processing 

• High-temperature reactor circulation systems 

• Biochemical and solvent transfer applications 

 

Operating Limits; 

Parameter	Value
Pressure	Up to 25 bar (362 psi)
Temperature	-40°C to +400°C (-40°F to +752°F)
Speed	Up to 3600 RPM
Size Range	20 mm to 200 mm (0.750” to 8.000”)

 

Engineering Note; 

Certain operating parameters, metallurgy selections, and API piping plans have been inferred based on standard industry practices for metal bellows double cartridge mechanical seals used in refinery and petrochemical services. Final selection should be verified against actual process conditions, vapor pressure, shaft dynamics, and applicable API 682 requirements prior to manufacturing.