1. Introduction
Mechanical seals are used in pumps, compressors, and other rotating equipment to prevent process fluids from leaking along the shaft and to keep contaminants out. Even after maintenance, leaks can still occur. Identifying the real causes is critical for effective repair.
2. Basic Structure and Operating Principle
Basic Components
A mechanical seal includes a rotating ring, a stationary ring, springs or other elastic elements, secondary seals such as O-rings, and a drive mechanism. The rotating ring moves with the shaft, while the stationary ring is fixed to the seal housing. Springs press the two rings together, and secondary seals block leakage along the shaft.
How It Works
The sealing faces stay in close contact under spring force. During operation, a thin fluid film forms between them, providing lubrication and helping maintain a tight seal. Combined with secondary seals, this system effectively contains the process medium.
3. Common Causes of Leakage After Maintenance
Installation Errors
Incorrect ring positioning or height leads to uneven contact and poor sealing. Assembling parts in the wrong order can damage O-rings or reduce spring preload. Scratches or dents on sealing faces from rough handling also cause leaks.
Worn or Defective Parts
Using worn rings without proper reconditioning or accepting poor surface finish after repair-weakens the seal. Aged, cracked, or swollen O-rings lose sealing ability. Weak or broken springs fail to maintain the needed contact force.
Changed Operating Conditions
Higher temperature, pressure, or more aggressive media can exceed the seal's design limits. Excessive vibration misaligns the sealing faces. Frequent pressure swings disrupt the fluid film and cause intermittent leakage.
Poor Maintenance Practices
Inadequate lapping leaves surfaces too rough or uneven. Residual dirt, oil, or particles left after cleaning can get trapped between faces, preventing full contact.
4. Practical Solutions
Install Correctly
Check dimensions before assembly. Follow the manufacturer's sequence. Handle sealing faces carefully-use protective covers when possible.
Replace What's Worn
Always inspect rings and replace them if worn. Ensure repaired surfaces meet flatness and roughness standards. Use compatible, high-quality O-rings. Test spring force and replace if weak.
Match Seals to Service Conditions
If process conditions change, verify that seal materials are still suitable. Fix vibration issues like misalignment or imbalance. Add dampeners if pressure fluctuates often.
Improve Repair Quality
Use proper lapping methods with fine abrasives. Clean all parts thoroughly with approved solvents and dry them completely before reassembly.
5. Conclusion
Leaks after maintenance usually result from multiple factors-installation mistakes, degraded parts, harsher operating conditions, or sloppy repair work. Addressing all these areas systematically ensures reliable sealing and longer equipment life.
