Common Failures of Sealing Rings

Sealing rings are the most fundamental yet critical "mission-critical components" across hydraulic, pneumatic, piping, valve, home appliance, and industrial equipment systems. Although they appear to be simple rubber rings, any issue with them can trigger a cascade of problems—such as oil, water, or air leaks, loss of pressure, abnormal equipment noise, and even system shutdowns.

A common misconception among many enterprises and equipment maintenance personnel is that a damaged sealing ring should simply be replaced with a new one. However, the cycle of repeated replacement and failure persists because the root cause of the malfunction has not been identified.

No. 1: Sealing ring hardens, crazes, and cracks due to heat

Symptom: After the equipment operates for a period, the sealing ring hardens and loses elasticity. Fine surface cracks (crazing) appear, followed by progressive cracking, material fragmentation, and media leakage; damage accelerates under thermal cycling conditions.

Root Causes:

1. Material temperature resistance is insufficient: Standard nitrile rubber undergoes rapid thermo-oxidative aging when operated above 100°C for extended periods; internal plasticizers volatilize, causing molecular chains to harden and become brittle.

2. High-temperature oxidative aging: The combined effect of high temperature and oxygen causes irreversible hardening and crazing of the rubber; this is the primary driver of natural aging.

3. Thermal cycling stress: Frequent equipment start-stop cycles cause repeated thermal expansion and contraction of the sealing ring, leading to fatigue cracking and eventual structural failure.

4. Long-term compression set: Rubber's resistance to compression drops significantly at high temperatures; after prolonged compression, it fails to recover its shape, leading to hardening and functional failure.

Solution:

Select the material precisely based on temperature (most effective approach)

1. Ambient temperature to 100°C: Use standard NBR (Nitrile Rubber); offers the best cost-performance ratio.

2. 100–180°C (steam or hot air applications): Switch to EPDM or VMQ (Silicone Rubber).

3. 180–250°C (high-temperature oil or industrial applications): Must switch to FKM (Fluoroelastomer).

4. Above 250°C (ultra-high-temperature chemical equipment): Select FFKM (Perfluoroelastomer) material.

No. 2: Minor or Persistent Micro-leakage at the Seal Ring

Symptom: No obvious physical damage to the equipment, yet persistent seepage (oil or water) or micro-leakage (gas) occurs at interfaces, shafts, or valve ports; system pressure cannot be maintained, and equipment efficiency drops.

Root Causes:

1. Insufficient compression or poor fit of the seal ring;

2. Wear on the seal groove or excessive clearance, preventing the O-ring from fully filling the gap;

3. Slight aging of the seal ring, resulting in reduced resilience;

4. Improper installation (e.g., lack of lubrication, incorrect seating, or slight twisting).

Solutions:

1. Check and control the compression level: The optimal compression range is 15%–30%; insufficient compression leads to leakage, while excessive compression causes damage;

2. When replacing the seal ring, use a lubricant compatible with the seal material; avoid dry or forced installation;

3. If the seal groove is worn or the clearance is excessive, install a PTFE back-up ring to help fill the gap;

4. Investigate system pressure fluctuations; frequent pressure pulses can destabilize the seal fit and cause micro-leakage.

No. 3: Sealing ring swelling, softening, deformation, and tackiness

Symptom: The sealing ring increases in volume, softens, and becomes sticky; it is difficult to install, extrudes out of the groove, and is prone to shearing damage.

Root Cause: Material incompatibility with the medium. Standard rubber lacks resistance to specific oils, solvents, cutting fluids, or chemical media; contact causes swelling or expansion—a classic case of failure due to chemical degradation. Many field failures stem from using the wrong material rather than temperature issues.

Solution:

1. Oil-based media: Prioritize the use of Nitrile rubber (NBR) or Fluororubber (FKM); do not use standard silicone rubber for long-term oil exposure.

2. Water vapor, steam, or acidic/alkaline environments: Use EPDM rubber.

3. Chemical solvents or corrosive liquids: Must use Fluororubber (FKM) or Perfluoroelastomer (FFKM).

4. Do not mix lubricants; use lubricants specifically suited to the sealing ring material to prevent chemical swelling.