Why Does the Mechanical Seal Leak?

A mechanical seal is designed to prevent fluid leakage between rotating equipment components, such as pumps, mixers, and reactors. However, leakage can occur due to many different reasons, including improper installation, incorrect seal selection, operating conditions, or equipment problems.

Understanding the causes of mechanical seal leakage helps users improve equipment reliability and extend seal service life.

1. Dry Running of the Seal Faces

One of the most common causes of mechanical seal failure is dry running.

Mechanical seals rely on a thin lubricating film between the rotating face and stationary face. When the seal operates without sufficient liquid lubrication, the sealing faces generate excessive heat, causing:

* Seal face damage
* Cracking of carbon faces
* Overheating
* Rapid wear

To avoid dry running, always ensure proper fluid circulation before starting the equipment.

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2. Improper Installation

Incorrect installation is another major reason for seal leakage.

Common installation problems include:

* Damaged O-rings during assembly
* Incorrect installation dimensions
* Dirty sealing faces
* Improper spring installation
* Misalignment between shaft and seal

The sealing faces must be clean, flat, and correctly aligned during installation.

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3. Wrong Mechanical Seal Selection

A mechanical seal must be selected according to the actual operating conditions.

Important factors include:

* Temperature
* Pressure
* Rotational speed
* Medium characteristics
* Chemical compatibility

For example, a standard carbon/ceramic seal may not be suitable for high-temperature chemical applications. In such cases, materials like silicon carbide, tungsten carbide, or special elastomers may be required.

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4. Excessive Vibration and Shaft Movement

Equipment vibration can damage mechanical seals.

Possible causes include:

* Shaft misalignment
* Bearing wear
* Pump imbalance
* Excessive shaft runout

Continuous vibration can cause uneven wear of sealing faces and lead to leakage.

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5. Damaged or Incorrect Elastomers

O-rings and rubber components provide secondary sealing.

Leakage may occur when elastomers are:

* Chemically attacked
* Swollen or hardened
* Cracked due to high temperature
* Incorrectly selected

Choosing the correct elastomer material, such as FKM, EPDM, or PTFE, is critical.

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6. Contaminated Sealing Medium

Solid particles in the fluid can damage the sealing faces.

Examples:

* Sand
* Metal particles
* Crystallized materials
* Slurry particles

For abrasive media, special seal designs such as hard face combinations or double mechanical seals may be required.

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7. Incorrect Operating Conditions

Mechanical seals may leak when actual operating conditions exceed design limits.

Problems include:

* Pressure exceeding seal rating
* Temperature exceeding material limits
* Running below minimum flow
* Frequent start and stop cycles

Always check that the seal operating conditions match the original design requirements