Common Causes of Mechanical Seal Failure in Pumps

Mechanical seal failure often occurs, but why?

Mechanical seals are critical components in rotating equipment, designed to prevent fluid leakage between the rotating shaft and stationary pump casing. While modern seal designs are highly reliable, failure remains a common cause of pump downtime. In most cases, the seal itself is not the root problem — is it a symptom of wider system or operational issues.

 

1. Dry Running

Dry running is one of the most destructive conditions for a mechanical seal. Seal faces rely on a thin lubricating film of the pumped fluid to prevent direct contact. Without it:

• Friction increases
• Heat builds up rapidly
• Seal faces crack, blister, or warp

Top tip: If a seal has been dry run, the face of it will be visibly damaged.

 

2. Poor Installation

Incorrect installation can lead to immediate or premature failure. Mechanical seals require precise alignment and correct handling. Typical issues include:

• Misalignment of shaft or seal faces
• Damaged O-rings during installation
• Transport clips on the left seal when running
• Contamination during assembly

Even minor installation errors can reduce seal life significantly.

 

3. Misalignment & Shaft Deflection

Excessive radial or axial movement places uneven load on seal faces. This leads to:

• Face wear
• Leakage
• Increased vibration
• Premature failure

Root causes may include worn bearings, pipe strain, or improper coupling alignment – vibration.

 

4. Excessive Pressure or Pressure Spikes

Mechanical seals are designed to operate within specific pressure limits. Exceeding these limits can:

• Force seal faces apart
• Overload secondary sealing elements
• Cause extrusion of elastomers

Pressure shocks from valve operation or system instability are common contributors.

 

5. Thermal Shock or Overheating

Rapid temperature changes can distort seal components due to differential thermal expansion. Common contributors:

• Flushing with cold liquid on a hot seal
• Inadequate cooling

Excess heat degrades elastomers and damages seal faces.

 

6. Cavitation & Vibration

Cavitation creates shock waves and vibration that damage seal faces and related components. Excessive vibration accelerates wear and disrupts proper face contact. This is often a system issue rather than a seal issue.

 

7. Abrasive Fluids Using a Water Seal

Solids in the pumped fluid can:

• Score seal faces
• Wear secondary seals

If you are pumping slurry, or contaminated fluids – a slurry rated mechanical seal must be used.

 

8. Chemical Attack

Incorrect material selection can result in:

• Elastomer swelling or hardening
• Corrosion of metal components
• Surface degradation of seal faces

Material compatibility with the process fluid must always be verified.

In many cases, mechanical seal failure is not a seal problem. Addressing root causes such as alignment, fluid condition, pressure stability, and correct material selection will dramatically improve seal reliability and reduce unplanned downtime.

Contact our team of experts if you are frequently experiencing seal failure.