Why Mechanical Seals Fail: Common Causes and Practical Solutions
Mechanical seals are one of the most critical components in pumps, mixers, agitators, and rotating equipment. Their role is simple but extremely important — prevent process fluid from leaking while allowing the shaft to rotate smoothly.
However, in most industries, mechanical seal failure is also one of the top causes of unexpected downtime, product loss, safety hazards, and maintenance cost escalation.
A single seal failure can stop an entire production line in a chemical plant, contaminate a batch in a pharmaceutical unit, or damage a pump in a water treatment facility. The good news is — mechanical seals rarely fail randomly. Almost every failure leaves clear warning signs and is usually caused by incorrect selection, installation, or operating conditions.
This guide explains the real reasons mechanical seals fail and the practical steps you can take to prevent them.
Understanding How a Mechanical Seal Works
A mechanical seal consists of two very precisely finished flat surfaces called seal faces.
• One face rotates with the shaft
• The other remains stationary in the housing
A very thin lubricating film (often only a few microns thick) exists between these faces. This micro-film is what prevents leakage while avoiding excessive friction and heat.
If anything disturbs this balance — heat, vibration, pressure fluctuation, or dry running — the seal faces get damaged and leakage begins.
Common Causes of Mechanical Seal Failure
1. Dry Running (The #1 Reason for Failure)
Dry running occurs when the pump operates without sufficient liquid at the seal faces.
Pump started without priming
Air pockets in the pipeline
The liquid film acts as a coolant and lubricant. Without it, the seal faces rub directly against each other. Within seconds, the temperature can rise above 200°C, causing:
Always prime pumps before start
Install dry-run protection sensors
Use proper venting procedure
Add level switches in tanks
Many seals fail within the first 24 hours, and the reason is usually incorrect installation — not seal quality.
Common installation mistakes
Touching seal faces with bare hands
Wrong tightening sequence
Using hammer force during fitting
Even small scratches on the seal faces can create leakage paths.
Follow manufacturer setting dimensions
Check shaft runout and alignment
Use pre-assembled cartridge mechanical seals whenever possible
3. Shaft Misalignment and Runout
Mechanical seals are precision components. Even a slight shaft wobble can break the seal face contact pattern.
Continuous dripping leakage
Frequent seal replacement
Improper coupling alignment
Check shaft runout with dial gauge
Inspect bearings regularly
Perform laser alignment for pumps
Maintain proper coupling gap
Heat is a silent killer of mechanical seals.
When temperature exceeds the seal design limit:
Elastomers harden or melt
Lubrication film evaporates
Faces distort (thermal distortion)
Use metal bellows mechanical seals for high temperature
Provide flush cooling arrangement
Use correct face materials (SiC vs Carbon)
Monitor operating temperature
5. Abrasive or Dirty Fluid
Slurry, sand, crystals, or solid particles entering the seal faces cause abrasion.
Common industries affected:
Effluent treatment plants
Install seal flush (API Plan 32/11)
Use hardened faces (Silicon Carbide)
Use double seals for slurry applications
Install strainers or filtration
6. Incorrect Seal Selection
This is one of the most overlooked issues.
A seal selected only by size instead of operating conditions will eventually fail.
Key parameters that must be considered:
For example:
Using a rubber bellows seal in a solvent chemical pump can cause elastomer swelling and leakage.
Choose seals based on application:
Single spring seals for water and clean fluids
Multi spring seals for higher pressure
Double mechanical seals for hazardous chemicals
Agitator seals for mixers and reactors
7. Pressure Fluctuation and Hydraulic Shock
Sudden pressure spikes or cavitation can push the seal faces apart momentarily, damaging them.
Avoid throttling at suction
Use pressure stabilizing systems
Install anti-cavitation measures
Warning Signs Before Seal Failure
Mechanical seals usually provide early indications before complete failure:
Steam formation near seal
Ignoring these signs often leads to pump damage as well.
Preventive Maintenance Checklist
Follow this checklist to extend seal life:
Inspect bearings periodically
Maintain correct operating temperature
Use correct seal material
How Proper Seal Selection Saves Cost
Many industries treat seals as consumables, but they are actually reliability components.
A properly selected and installed seal can:
Reduce maintenance frequency
Prevent product contamination
Avoid production downtime
Mechanical seal failure is rarely due to manufacturing defects. In most cases, failure results from operating conditions, incorrect installation, or improper selection.
By understanding the real causes — dry running, misalignment, heat, pressure, and contamination — industries can dramatically improve equipment reliability and reduce maintenance costs.
Instead of repeatedly replacing seals, the focus should be on root-cause correction and proper engineering selection.
Connect with Cosmos Seals – Industrial Sealing Experts
If you are facing recurring leakage or short seal life, it usually indicates a selection or application issue, not just a replacement issue.
Cosmos Seals provides application-engineered solutions including Single Spring Mechanical Seals, Multi Spring Mechanical Seals, Double Mechanical Seals, Cartridge Mechanical Seals, Metal Bellows Mechanical Seals, Rubber Bellows Mechanical Seals, Pump Shaft Seals, Agitator Seals, and Customized Mechanical Seals for diverse industries such as chemical, pharmaceutical, water treatment, marine, and power plants.
Our team helps you select the right seal based on operating parameters — pressure, temperature, RPM, and fluid characteristics — ensuring long service life and reliable operation.
🌐 Website: https://cosmosseals.com
