Mechanical seals are used to prevent fluid leakage along the rotating shaft of a pump or other rotating equipment, such as mixers and compressors. A mechanical seal forms a controlled seal between the rotating shaft and the stationary pump housing or casing, preventing process fluid from escaping into the surrounding environment.
There are several types of mechanical seals available for the wide range of applications in which pumps are used. Each type has its own advantages and limitations, making the correct seal selection important for reliable pump operation.
1. Single Mechanical Seal
📐 Design:
One set of seal faces – a rotating face and a stationary face
A single elastomer, such as an O-ring, for secondary sealing
Typically spring-loaded to maintain contact between the seal faces
📦 In Stock, Ready to Ship:
N6
N7
N8
N9
N10
N21
N560
✅ Pros:
Simple and cost-effective
Easy to install and maintain
Suitable for many clean, non-hazardous fluids
❌ Cons:
Small amounts of leakage can occur through normal seal face operation
Not ideal for toxic, abrasive or high-pressure fluids
Susceptible to damage from dry running
🛠️ Applications:
Water and wastewater treatment
Irrigation pumps
HVAC circulation systems
General industrial utility pumps
2. Double Mechanical Seal
Double mechanical seals use two sets of seal faces and are designed for applications where additional protection against leakage is required. Depending on the configuration, a barrier or buffer fluid is circulated between the two seals.
📐 Design:
Two sets of seal faces
A barrier or buffer fluid is circulated between the seals
Pressurised or unpressurised depending on the configuration
📦 In Stock, Ready to Ship:
560D6
🔄 Common Arrangements:
Back-to-back: Seal faces are positioned away from each other and typically use a pressurised barrier fluid.
Tandem: A secondary seal provides additional protection and acts as a backup to the primary seal.
Face-to-face: Both seal faces are positioned towards each other. This arrangement is less common and can be more complex.
✅ Pros:
Very low leakage to atmosphere
Can handle hazardous, abrasive, high-pressure and high-temperature services
Can extend seal life in demanding operating conditions
❌ Cons:
More expensive and complex than single seals
May require a dedicated seal support system, such as API Plan 53 or 54
Requires additional installation and maintenance
🛠️ Applications:
Petroleum and chemical processing
Pumps handling toxic or flammable fluids
Slurry pumps in mining
Pumps handling polymers, resins or caustic fluids
High-pressure boiler feedwater systems
3. Cartridge Seal
📐 Design:
Preassembled unit with all components aligned and sealed
Includes gland, sleeve, seal faces and secondary seals
Available in single or double configurations
📦 In Stock, Ready to Ship:
N3
N3RD
N3LU
✅ Pros:
Simplified installation helps minimise human error
Less downtime and easier replacement
Ideal for plants with limited technical staff
❌ Cons:
Higher initial cost
May have size or compatibility constraints with some older equipment
🛠️ Applications:
Refineries and power plants
Food and beverage production
OEM pumps for packaging and processing systems
4. Bellows Seal
Bellows mechanical seals use a flexible bellows element instead of a conventional spring arrangement to maintain contact between the seal faces. Bellows seals are available with either metal or elastomer bellows, depending on the application.
📐 Design:
Uses a bellows element to maintain contact between the seal faces
Metal bellows are suited to high-temperature and demanding chemical applications
Elastomer bellows are generally suited to less demanding applications
📦 In Stock, Ready to Ship:
NG1
NG12
NG13
✅ Pros:
No dynamic O-ring sliding along the shaft
Well suited to certain sticky, viscous or crystallising fluids
Metal bellows can perform well in high-temperature or corrosive environments
❌ Cons:
Generally more expensive than conventional seal designs
Metal bellows can be subject to fatigue over time
🛠️ Applications:
Chemical reactors and high-temperature applications
