The different types of leakage

The leak rate is changing – It gets better or worse.

  • This type of leak is usually associated with seal face leakage because the seal face is a wearable surface.
  • The carbon seal face is not flat.
  • The seal face was damaged at the time of assembly.
  • Dirt or solids are imbedded into one of the faces
  • Coke (over heated oil) or some other solid has formed on the seal faces causing them to separate.
  • The rotating face is hung up on the shaft.
  • Outside seal springs have been painted during routine maintenance.
  • The hard stationary face has been installed backwards. These faces are usually lapped on only one side

The faces spit liquid or vapor.

  • The product is vaporizing at the faces. Check the fluid vapor point. When using balanced seals the stuffing box pressure must be at least one atmosphere higher than the product vapor point. Unbalanced seals require a much higher differential pressure.
  • The rotating face is running off of the stationary face.
  • The stationary seal face was not centered to the shaft.
    • The seal is not concentric with the shaft.
    • The rotating assembly is out of balance.
    • The shaft is bent

Fire hose type leakage. The leak is following shaft rotation.

  • Product has solidified on the seal face and a piece has broken off. A high temperature between the faces often initiates this.
  • The rotating face is cracked.
  • The hard surfacing, or coating, is lifting off of the rotating face.

Intermittent leakage.

  • Temperature changes or pressure surges are altering the face flatness within the elastic range of the material.
  • The stuffing box is alternating between vacuum and pressure
  • The movable face is sluggish and not able to follow run out.
    • The product is viscous.
    • The product has started to solidify.
    • The shaft/ sleeve is too large in diameter and it is restricting movement of the seal. Spring loaded dynamic elastomers such as Teflon® wedges, U- cups, chevrons and spring loaded O-ring designs are very sensitive to this problem
    • Dirt or solids are clogging the seal and preventing it from following shaft run out. Designs that use multiple springs in the fluid are prone to this problem.
    • In a non O-Ring version, the spring load is too high causing the elastomer or Teflon® to stick to the shaft. Some designs use spring loaded O-rings that experience the same problem.
  • The product is occasionally vaporizing between the faces.
  • There is a leak between the face and the holder that becomes visible only when the unit comes up to operating temperature.
  • A bending or bent shaft is causing the seal outside diameter to contact the inside diameter of the stuffing box, or some other stationary object.
  • The pump is running with too high or too low a head. This causes a shaft deflection that may be excessive. Check the pump curve against actual operating conditions.
  • The application is cycling between ambient and cryogenic temperatures causing the elastomer to harden on the cold cycle and the faces to go out of flat.

The seal area is damp. There is no visible leakage.

  • There is a leaking flange or fitting above the seal that is dripping close to the seal location.
  • The product is vaporizing. Hold a clean piece of white paper over the running seal, and check for leakage. The paper will become damp.
  • Any condition that could cause intermittent leakage will cause this problem.

Constant dripping. It gets neither better nor worse. This leak cannot be caused by a damaged carbon seal face because carbon seal faces are a wearable surface and the leak rate would have to change.

  • The elastomer (rubber part) is cut or nicked.
  • The shaft/sleeve is damaged at the elastomer location.
  • There is damage in the O-ring groove. Maybe the O-ring was removed with a sharp metal instrument and this has caused a scratch in the O-ring groove.
  • There is a leak path between the carbon and the carbon face holder.
  • Leaking between the cartridge sleeve and the shaft.
  • Leaking between the shaft sleeve and the shaft.
  • Leaking between the gland and the stuffing box. This leak path is very visible in most applications
  • Leaking between the stationary face and the seal gland.
  • The seal faces are stuck open.
  • You are using two hard faces. Either one or both are not flat
  • The elastomer has swollen up due to chemical attack by either the product, the flush, what ever is being used to clean the lines, or by the lubricant that was put on the elastomer to help the installation. This attack usually takes place within one week of exposure to the non-compatible lubricating fluid.


  • On February 18, 2018