Mechanical Seal Troubleshooting Guide: Common Causes of Leakage and How to Fix Them

Verseel > BLOG > Mechanical Seal Troubleshooting Guide: Common Causes of Leakage and How to Fix Them

Last update: 8/22/2025

Mechanical seals are essential components in pumps, compressors, and other rotating equipment. By creating a good seal between the stationary equipment housing and the rotating shaft, they prevent fluid leakage and help ensure equipment reliability.

When a mechanical seal begins to leak, however, the consequences can range from minor inefficiencies to significant safety hazards—especially in industries handling hazardous fluids. This guide covers the most common types of seal leakage, what they mean, and how to fix them.

What Is a Mechanical Seal?

A mechanical seal is designed to prevent leakage between two mating surfaces, typically in rotating equipment such as pumps, compressors, and mixers. It consists of two main parts:

  • A stationary face fixed to the equipment housing

  • A rotating face connected to the shaft

These faces are pressed together with the help of springs or other mechanisms, maintaining a seal even under high pressures and temperatures. For more background on seal types and standards, see the Fluid Sealing Association.

Common Causes of Mechanical Seal Leakage

1. Leakage Between the Pump Shaft and Seal Sleeve

If leakage is observed here, the sleeve O-ring is often the culprit. Damage typically occurs during installation when sharp edges or burrs on the shaft cut into the O-ring.

Solution: Replace the O-ring and carefully prepare the shaft before reinstalling.

2. Leakage Between the Seal Gland and Collar

This usually signals either:

  • A damaged seal face, or

  • A damaged internal O-ring

Leakage may appear at startup or during operation.

Solution: Remove the seal, inspect for damage, and replace affected components.

3. Leakage Between the Pump Seal Chamber and Seal Gland

This type of leakage often points to a gland gasket issue. If the gasket isn’t torqued evenly during installation, it can allow fluid to escape.

Solution: Check the gland bolts and tighten as needed. If the seal is still leaking from the same place, reinstall the seal with a new gasket, ensuring even torque. Refer to industry installation standards like API 682 for best practices.

4. Slow Drip From the Seal

A slow drip is not always catastrophic, but it should be monitored closely:

  • If the fluid is non-hazardous, the drip may be tolerable until it worsens.

  • If the fluid is hazardous, the seal should be replaced immediately.

In some cases, seals may drip when static but seal dynamically once the pump is running. Additionally, it’s possible that the pump is out of tolerance for what is required for proper mechanical seal installation and performance. See our installation requirements for more details. 

5. Smoke Coming From the Seal

Smoke indicates friction and heat, often because the seal is running dry (without lubrication from the pumped fluid).

Solution: Shut down the pump immediately. Damage has likely occurred, and the seal will need replacement. In some cases, smoke during startup may be due to set clips left in place. If caught quickly, removing the clips may resolve the issue.

6. Seal Sleeve O-Ring Damage After Startup

If the sleeve O-ring alone is damaged, it may indicate that the pump shaft rotated independently of the seal sleeve. This occurs when set screws are not fully engaged.

Solution: Ensure all set screws are properly tightened and torqued prior to startup.

7. Should You Pressure Test a Seal After Installation?

While not required by formal standards, performing a pressure decay test after the seal has been installed on the pump is considered best practice.

How to test:

  1. Pressurize the seal chamber with air to 25 psi.

  2. Isolate the pressure source.

  3. Time for 5 minutes and observe.

    • A drop of less than 2 psi = seal passes.

    • A drop of more than 2 psi = seal failed and requires inspection.

Key Takeaways

  • Most seal leaks prior to pump startup are caused by damaged O-rings, gaskets, or improper installation.

  • Slow drips may be acceptable depending on the fluid type, but hazardous leaks demand immediate action.

  • Smoke from seals indicates serious problems—shut down the equipment immediately.

  • Pressure testing is a proactive way to confirm correct installation before startup.

By understanding these common issues and applying best practices, facilities can improve reliability, reduce downtime, and extend the life of their mechanical seals—all while maintaining compliance with environmental standards.

For additional information, visit our frequently asked questions (FAQ) page or contact us with any questions regarding seal troubleshooting.

Tags: mechanical seals, seal leakage, pump seal troubleshooting, O-ring damage, gland gasket, mechanical seal installation, pump startup