Mechanical Seals Function, Failure, and Fixes

In rotating equipment like pumps, mixers, and compressors, one of the most critical but often overlooked components is the mechanical seal. This small yet powerful device plays a major role in maintaining system integrity, preventing fluid leaks, and protecting machinery from wear and contamination.

In this blog, we’ll explore what mechanical seal is, how they work, where they’re used, and why proper selection and maintenance are essential for long-term equipment performance.

What Is a Mechanical Seal?

A mechanical seal is a device that joins systems or mechanisms together by preventing leakage, containing pressure, and excluding contamination. It does this by creating a tight seal between the rotating shaft and the stationary housing (or pump casing).

Mechanical seals are most commonly used in:

• Centrifugal pumps

• Mixers and agitators

• Compressors

• Propeller shafts (marine applications)

How Does a Mechanical Seal Work?

A mechanical seal typically consists of two main components:

• Rotating face (attached to the shaft)

• Stationary face (mounted to the pump housing)

These faces are held together under spring pressure. A very thin film of fluid forms between them, providing lubrication while preventing leakage. The precision between the faces—flat to within microns—ensures the seal remains tight even under pressure and high-speed rotation.

The design may also include:

• Secondary seals (O-rings or gaskets)

• Springs or bellows for axial movement

• Set screws or drive collars for stability

Types of Mechanical Seals

There are several types of mechanical seals, each designed for specific operational environments:

• Balanced vs. Unbalanced Seals
  Balanced seals are used in high-pressure applications; unbalanced are simpler and used in low-pressure systems.

• Pusher vs. Non-Pusher Seals
  Pusher seals use springs to maintain contact and are more versatile; non-pusher designs (such as bellows) prevent clogging and are ideal for dirty fluids.

• Single vs. Double Seals
  Single seals are common in standard applications. Double seals (back-to-back or tandem) provide extra protection in hazardous or high-pressure environments.

• Cartridge Seals
  Pre-assembled units that simplify installation and reduce the risk of misalignment—a popular choice in industrial and marine applications.

Applications of Mechanical Seals

Mechanical seals are critical in industries such as:

• Marine and Shipbuilding – Shaft seals for pumps, compressors, and propeller shafts

• Oil and Gas – High-pressure and hazardous fluid containment

• Food and Beverage – Sanitary seals for mixers and processing equipment

• Pharmaceutical and Chemical – Preventing contamination and leakage of sensitive materials

• HVAC and Water Treatment – For long-lasting pump performance

Common Causes of Seal Failure

Despite their precision, mechanical seals can fail due to several preventable reasons:

• Improper installation

• Dry running (lack of lubrication)

• Chemical or abrasive wear

• Excessive vibration or shaft misalignment

• Thermal shock or pressure surges

Early detection and preventive maintenance can greatly extend the life of a seal and prevent equipment downtime.

Tips for Selecting the Right Mechanical Seal

Choosing the correct mechanical seal depends on several factors:

• Operating pressure and temperature

• Type of fluid (clean, corrosive, abrasive)

• Shaft speed

• Regulatory requirements (e.g., food-grade, explosion-proof)

• Ease of installation and maintenance

Consulting with seal manufacturers or using a seal selection guide can help match the correct seal to your specific application.

Maintenance and Best Practices

To maximize the life and performance of mechanical seals:

• Use appropriate flushing or cooling systems

• Maintain alignment and minimize shaft deflection

• Regularly inspect for wear or surface damage

• Avoid running equipment dry

• Replace seals at recommended service intervals

Advantages of Mechanical Seals Over Traditional Packing

Many industries have moved away from traditional gland packing in favor of mechanical seals. Here’s why:

• Superior Sealing: Less leakage and better control of fluid loss.

• Lower Maintenance: No need to constantly adjust packing rings.

• Reduced Friction and Heat: Minimizes shaft wear and energy consumption.

• Longer Service Life: Especially in abrasive, corrosive, or high-speed applications.

• Cleaner Operation: Ideal for food, pharma, and clean water systems.

Environmental Considerations

Mechanical seals contribute to environmental protection and regulatory compliance by:

• Reducing emissions of hazardous fluids

• Preventing leakage into waterways or sensitive environments

• Supporting energy efficiency through lower power consumption

• Enabling compliance with EPA, IMO, FDA, and other regulatory standards

Innovations in Mechanical Seal Technology

Recent advancements have improved mechanical seal reliability and versatility:

• Split Seals: Easy to install without dismantling equipment

• Gas-Lubricated Seals: Used in dry-running or high-speed compressors

• Magnetic Drive Seals: Non-contact, no friction, ideal for zero-leak applications

• Engineered Materials: Use of silicon carbide, carbon graphite, PTFE, and Hastelloy for extreme environments

How to Troubleshoot Common Seal Problems

Here’s a quick reference for common seal issues and what they might indicate:

Industries That Rely on Mechanical Seals

Highlighting specific industries can help illustrate their wide range of use:

• Power Generation – Cooling and feedwater pumps

• Mining – Slurry handling and dewatering pumps

• Textile – Dye circulation systems

• Pulp & Paper – High-temperature chemical pumps

• Desalination – High-pressure brine circulation systems

Conclusion

Mechanical seals may not be the most visible part of your machinery, but they are absolutely vital to performance, safety, and efficiency. Understanding how they work—and how to care for them—can save you from costly repairs and unplanned downtime.