Seal Failure: Common Causes and Cures

In the world of machinery, repair and maintenance is a simple fact of life. So, it should come as no surprise that when it comes to sealing products being used for hydraulic and pneumatic applications, wear and tear is inevitable

Even when you have diligently installed the most robust product, in the best kind of material, certain factors will always lead to seals eventually having to be replaced.

Thankfully in most cases, problems can be identified early, before any serious operational damage can occur, and seals are easily reinstated.

Here we take a look at typical seal failure, the likely causes, and what can be done to rectify the problem.


Hardening of the dynamic face has caused glazing and cracks.

Cause: Heat generated by high speed.

Cure: Slow stoke speed or use an alternative seal device.

The whole seal has gone hard and elasticity is lost.

Cause: High fluid temperature, deterioration of fluid or problem with the compatibility of the seal to the fluid.

Cure: Lower the oil temperature, renew fluid or change to a different seal compound.


The dynamic face of the seal is worn to a glossy mirror-like finish.

Cause: Insufficient lubrication

Cure: Check oil viscosity or use an alternative seal device.

Wear on dynamic lip of seal is egg-shaped.

Cause: Rod or piston bore is not concentric

Cure: Hone to within seal specifications or replace the worn rod or cylinder tube.

Signs of abnormal wear on one side of the dynamic lip.

Cause: Worn bearing or wear ring. Excessive lateral load.

Cure: Replace bearings. Increase bearing area.


Cut or dent on the lip.

Cause: Storage on a nail or peg. Improper installation tool

Cure: Store flat in a plastic bag in a closed cardboard box. Installation tools should not have sharp edges.

Scratched on the dynamic side.

Cause: Scars on the rod or bore or foreign material in fluid

Cure: Hone, polish and deburr metal parts or flush the system.


Material is soft and misshaped.

Cause: Absorption of fluid. Fluid and seal are incompatible or the there is water in the system.

Cure: Change the seal compound or system fluid. Or flush the system.


Cracks and loss of elasticity. The material easily crumbles.

Cause: High fluid temperature. Exposure to ozone or sunlight.

Cure: Lower oil temperature. Store seals away from sunlight and arc welding area.


Axial cuts on the dynamic side.

Cause: Metal chips or other foreign material in system. Imploding air bubbles.

Cure: Flush System. Bleed air from the system.


Extruded material on the dynamic side of heel

Cause: Gap between mating surfaces is too wide, worn bearings or extreme pressure.

Cure: Employ a back ring, replace the bearings or use an alternative seal.

Extruded material on the static side of the seal.

Cause: Uneven support surface or undersized back-up ring.

Cure: Machine surface. Correct back up size.


Chunks of material torn from the dynamic side.

Cause: Excessive back pressure.

Cure: Check relief valves.

Pressure side of seal burned and broken.

Cause: Explosion of residual air at high pressure. ‘Dieseling’

Cure: Bleed air from the system.

Long cracks in the “V” portion of the seal.

Cause: Frequent high pressure shocks or spikes. Low temperature start-up.

Cure: Use alternative style seal. Warm system before applying pressure.

Breaking off of entire dynamic side.

Cause: Deterioration of material and/or fluid.

Cure: Use alternative material or seal. Flush system.

Replacement seals and seals kits, for most applications can be found off the shelf and despatched to you quickly.

If you require any further advice regarding seals and their application, the team of experts at FPE Seals can help you source what you need.

Can’t find what you’re looking for? We can also custom-manufacture a full range of seals, in a full range of materials to meet your exact requirements.

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