Damage to the springs


Broken or cracked.

  • The stationary face is not perpendicular to the shaft causing excessive spring flexing in the metal “plastic range”. The spring material has “work hardened” and fatigued.
  • Chloride stress corrosion problems with 300 series stainless steel spring material.


  • Stressed material corrodes much faster than unstressed material. The springs are under severe stress.


  • If the product solidifies or crystallizes, it can clog springs exposed to the pumped fluid.
  • Be sure to distinguish between “cause and effect”. If the springs are located outside the liquid it means that the clogging probably happened after the seal failure.
  • Dirt or solids in the fluid can clog exposed springs. Most raw product has enough solids to do this.
  • The springs in some outside and cartridge mechanical seal designs are sometimes painted by maintenance personnel.


  • Almost always an assembly problem. The seal face drive lugs were not engaged in their anti-rotation slots. This is a problem with many seal designs. Check to see if your seals can come apart easily or if the drive lugs can change position when the seal is not compressed.

The drive lugs or slots are worn on both sides.

  • Excessive vibration.
  • The single spring, rubber bellows seal was not vulcanized to the shaft.
  • The stationary is not perpendicular to the shaft, causing excessive spring and lug movement in some designs.

Broken metal bellows.

  • Fatigue caused by over flexing of the bellows in the plastic range of the metal
  • Harmonic vibration.
  • Slipstick.
  • The discharge recirculation line is aimed at the thin bellows plates.
  • Excessive wear from solids in the stuffing box.
  • Faces sticking together as the product solidifies.
  • Chloride stress corrosion with 300 series stainless steel.

Because some of these metal bellows seals do not have a dynamic elastomer to provide vibration damping, some other means must be provided, or vibration will always be a problem.