Bellows Mechanical Seals

Bellows mechanical seals are advanced sealing solutions used in pumps and other rotating equipment, characterized by a flexible, accordion-like bellows element that eliminates the need for dynamic secondary seals (like O-rings or pushers). This design offers high reliability and durability, particularly in high-temperature or corrosive applications.
Key Features and Benefits
No Dynamic O-Ring: The bellows provides the necessary flexibility and axial movement to maintain seal face contact, eliminating the common issue of dynamic O-ring hang-up or sticking caused by debris, chemical attack, or shaft fretting.
High Temperature Capability (Metal Bellows): Metal bellows seals are ideal for extreme temperature applications (cryogenic to over 400°C), as they use metal instead of elastomers that would degrade in heat.
Corrosion Resistance: Available in a wide range of corrosion-resistant alloys (e.g., Hastelloy, AM350, Titanium), making them suitable for handling aggressive chemicals. Elastomer bellows offer resistance specific to their material (e.g., EPDM, Viton®).
Reduced Fretting and Shaft Damage: By eliminating dynamic O-rings, these seals prevent fretting corrosion on the shaft or sleeve, extending the life of the mating equipment.
Self-Cleaning: The flexible, non-clogging design of the bellows allows small solids to pass through without interfering with seal operation, which is an advantage over multiple-spring designs.
Common Types and Construction
Bellows mechanical seals are primarily categorized by the material used for the bellows element:
Metal Bellows Seals:
Description: The bellows is formed from thin, welded metal diaphragms (welded metal bellows) or hydroformed from a single tube (formed metal bellows).
Use Cases: Standard for high-temperature applications (hot oils, steam, aggressive chemicals), high pressures, and services with extreme temperatures where elastomers cannot be used.
Elastomer Bellows Seals:
Description: The bellows is molded from a flexible rubber material such as NBR, EPDM, or Viton®.
Use Cases: Suitable for general-purpose applications with clean, safe fluids (water, mild chemicals, general oils) at lower temperatures and pressures. They are cost-effective alternatives to more complex metal or multiple-spring seals.
PTFE Bellows Seals:
Description: Made entirely or predominantly of PTFE or filled PTFE for maximum chemical resistance.
Use Cases: Ideal for highly aggressive chemical services where no other material will work, although they have lower pressure ratings and are generally for lower-speed, unbalanced applications.
Applications
Bellows mechanical seals are used in demanding applications across various industries:
Oil and Gas/Petrochemicals: In refineries and processing plants for handling hot hydrocarbons, corrosive chemicals, and volatile fluids.
Power Generation: Used in boiler feed pumps, steam turbines, and other high-temperature equipment.
Chemical Processing: For pumps and mixers handling a wide range of aggressive acids, bases, and solvents.
Pulp and Paper Industry: Selected for their robust design that handles the harsh conditions and fibrous materials common in the process.