Maintenance of mechanical seals for pumps

### Common Leakage Points in Pump Mechanical Seals

Mechanical seals in pumps are prone to leakage at five critical points:

1. **Seal between the sleeve and the shaft**

2. **Seal between the dynamic ring and the sleeve**

3. **Seal between the dynamic and static rings**

4. **Seal between the static ring and the static ring seat**

5. **Seal between the sealing end cover and the pump body**

Leakage at the shaft or sealing end cover is easier to detect and resolve, especially with careful observation. However, leaks in other areas, such as between the dynamic and static rings, are harder to identify visually. Diagnosing these issues requires analyzing leakage symptoms and understanding the pump's structure.

### Causes of Leakage and Troubleshooting

1. **Leakage During Static Testing**

- After installation, a static test is performed to check for leaks.

- **Small leaks** often indicate issues with the dynamic or static seals.

- **Large leaks** suggest problems with the friction pair (dynamic and static rings).

- **Manual cranking** can help identify the source:

- If leakage doesn’t change, the issue lies in the static or dynamic seal.

- If leakage varies, the friction pair is likely at fault.

- **Axial spray** indicates a dynamic seal failure, while **spray in all directions** points to a static ring seal issue.

2. **Leakage During Test Runs**

- High-speed rotation during operation suppresses leakage due to centrifugal force.

- If leakage persists, it is likely due to damage to the friction pair caused by:

- **Axial forces** from vacuum, cavitation, or pressure buildup.

- **Excessive compression** during installation, leading to wear or scratches.

- **Improper seal tightness**, causing dynamic or static ring misalignment.

- **Granular substances** in the medium damaging the seal faces.

- **Incorrect design or material selection**, resulting in poor sealing under operating conditions.

3. **Sudden Leakage During Normal Operation**

- Sudden leaks are often caused by:

- **Changes in operating conditions**, such as vacuum or cavitation.

- **Heat buildup** from low pump output or high recirculation.

- **Sediment accumulation** in the pump.

- **Adhesion of friction pairs** after prolonged inactivity.

- **Increased impurities or polymerization** in the medium.

- **Environmental or operational changes**, such as rapid temperature shifts or frequent adjustments.

- **Sudden shutdowns** without proper restart procedures.

### Common Misconceptions in Seal Maintenance

1. **"Tighter is better" for springs, seals, or locknuts.**

- Excessive compression causes rapid wear, deformation, or stress damage. Proper tension ensures elasticity and adjustability.

2. **"New is always better than old."**

- While new seals are generally preferred, improper material selection or dimensional errors in new seals can lead to failures. In some cases, leaving an old seal in place may provide better adhesion and sealing.

3. **"Repair is always necessary."**

- Not all leaks require immediate repair. Adjusting operating conditions or seals can sometimes resolve issues without disassembly, saving time and resources.

Proper diagnosis, careful installation, and adherence to maintenance best practices are essential for minimizing pump seal failures and ensuring reliable operation.