Sealing System Leakage Analysis - Seal Lip

 

 

Lack of Wear

Probable Causes	Actions or Countermeasures
No interference with the shaft.	Check seal ID for missing garter spring. Check shaft diameter. Observe shaft for evidence of contact. Look for concave distortion on outside face of seal.
Very light interference with the shaft.	Check seal ID for low radial load. Look for concave distortion on outside face of seal.
Seal installed backwards.	Check installation method and teardown report.
Heavy continuous leakage from startup, possibly from another source.	Check fluid consumption reports-look for excessive media outside the seal area. Check shaft size and seal interference. Leakage may be occurring through a defect; check seal ID and shaft for defects.
Dynamic lift-off from centrifugal force, flutter or stick slip action.	Check for low radial load and spring presence. Check lip opening pressure on shaft size mandrel.
Reverse hydrodynamic pumping.	Check shaft rotation direction with helix direction. Check for spiral lead or axial scratches on the shaft.

 

---

Excessive Wear

Probable Causes	Actions or Countermeasures
Excessive interference - wide wear path.	Check seal ID and shaft size (interference).
Excessive radial force - wide wear path	Check for high radial load. Look for small ID garter spring.
Excessive pressure on lip - concave wear path.	Check system pressure at operation conditions.
Rough shaft finish.	Inspect shafts for defects. Measure surface finish.
Insufficient lubrication at seal lip.	Provide lubrication on air side of seal or between lips

 

---

Eccentric Wear

Probable Causes	Actions or Countermeasures
Seal cocked in assembly.	Check shaft for wide wear path. Check installation procedure and equipment.
Excessive radial wall variation of lip.	Measure seal radial wall variation and relate to wear pattern.
Excessive shaft to bore misalignment.	Check shaft to bore offset.
Angled or cocked shaft.	Check shaft alignment, excessive run-out or bent shaft.
Side load applied to shaft.	Check possible side deflection or lose bearings.

 

Below is an example of eccentric wear. As you can see, the wear path is wider on one side.

 

 

---

Nicks, Scratches or Cuts at Lip Contact Area

Probable Causes	Actions or Countermeasures
Sharp edge or burrs on end of shaft.	Inspect shaft for burrs or sharpness.
Sharp edge or burrs on installation tool.	Check installation device for sharp edges or burrs.
Seal installed over keyway or splines.	Provide installation sleeve for splines or keyways
Trimming knife cuts.	Check suppliers knife trimming methods.
Nibbled appearance at sealing edge.	Defects may be caused by bulk finishing or handling by supplier.
Cuts from packing methods.	Check suppliers packaging and shipping methods.

 

Below is an example of a cut seal lip.

 

---

 

 

Tears or Separations in Lip Area

Probable Causes	Actions or Countermeasures
Stress fatigue in flex section.	Check system pressure. Seal may be deformed in ID flex section.
Bond separation at ID of metal case.	Check seal for bond, burrs, and blisters.
Migration of low temperature crack.	Check lip contact area of minor cold cracks. Suspect severe side load at lot temperatures.
Circumferential tear behind lip.	Look behind lip at base for circumferential tear caused by pressure or fatigue.
Caused during assembly or removal.	Review teardown and seal removal methods and check tools used.

 

Below is an example of poor bond. You will know if you have a bond problem when the separation between the rubber and metal component is "Clean" and there are no rubber particles attached to the metal component .

 

 

---

 

Hardening or Cracking of Rubber

Probable Causes	Actions or Countermeasures
Prolonged or excessive high temperature exposure.	Check rubber spec. versus system temperature profile.
Flexing of lip at low temperatures below rubber capability.	Check rubber spec. versus system temperature profile. Check offset, runout, and sideplay.
Extended dry running causing localized high temperature under the lip.	Check fluid level. Check for shaft that is too smooth.
Cracking from disassembly or observation techniques.	Review procedures and look for other damage.
Ozone exposure.	Check other dry areas of rubber. Consider excessive solar or electrical exposure.

 

Below is an example of a seal that has signs of heat cracking.

 

 

 

---

 

Measure ID and Radial Load

Probable Causes	Actions or Countermeasures
Measure ID using non contact device.	Use optical comparator or linear scope. Record min/max readings and relate to leak.
Measure wear pattern width and variation.	Use optical means, photographic, or cross section in comparator.
Compare profile with profile of unused seal.	Section seal and mount on glass slide for magnified comparator viewing.
Measure radial ID force.	Use electronic split mandrel type radial load device.

 

---

 

Cocked Oil on Lip

Probable Causes	Actions or Countermeasures
Hard and glazed deposit in ID.	Possibly decomposed fluid. Scrape off and analyze.
Insufficient hydrodynamic pumping action.	Helices ineffective.
Excessive under lip temperature.	Check specification of fluid versus operating parameters.

 

---

 

Softening or Swelling

Probable Causes	Actions or Countermeasures
Volume change of material very high.	Refer to elastomer physical data and check fluid.
Reversion.	Check elastomer/fluid compatibility specification.
Exposure to solvent used during teardown.	Review teardown procedure and elastomer compatibility with solvents.
Operational contamination of fluid being sealed.	Check for possible exposure to unspecified media coming in contact with seal.

 

Below is an example of a seal with fluid compatibility problems.

 

 

---

 

Inverted Lip Due to Poor Installation

Probable Causes	Actions or Countermeasures
Oil to air side shaft assembly.	Provide installation aid such as a bullet nose for shaft.
Lack of proper concentricity assembly.	Provide centering aide for assembly such as locating pins.

 

---

 

 

Go back to the top