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Technical Information

Defects and Countermeasures

O-ring

A summary table of common defects that occur when using O-rings and their corresponding countermeasures is provided for reference.

Classification by failure Phenomenon Causes Countermeasures
Extrusion

The O-ring extrudes from the groove due to high fluid pressure.

 1. The pressure is too high
2. The clearance is too large.
3. No back-up ring is used. 		1. Narrow the clearance.
2. Increase the rubber hardness.
3. Use a back-up ring.
Compression set

The compressed section becomes permanently flattened.

1. The temperature is too high.
2. A material with poor compression set resistance is used.
3. The O-ring was insufficiently vulcanized. 		1. Replace with a material that has good resistance to compression set.
2. Cool the seal area.
Hardening due to oxidation and heat

The rubber hardens. Initially, it occurs on the surface and then progresses throughout the entire cross-section. A compression set accompanies it.

1. The temperature is too high.
2. Crosslinking of the rubber material and evaporation of plasticizers. 		1.Select materials with good high-temperature properties and heat resistance.
2.Lower the operating temperature.
3. Prevent the surface from exposure to oxygen.
Extraction of plasticize

The volume decreases.
The dimensions shrink.
The rubber hardens.

1. The temperature is too high.
2. Crosslinking of the rubber material and evaporation of the plasticizer.		 Use a rubber material with low plasticizer content or one that contains a plasticizer that is difficult to extract.
Wear

Linear wear occurs on the contact surface, parallel to the direction of motion.

1. The mating surface is too rough or too smooth.
2. Poor lubrication.
3. High temperature and excessive dust. 		1. Properly finish the surface.
2. Improve lubrication.
3. Select a suitable rubber material.
4. Prevent dust intrusion.
Ozone cracks

Numerous small cracks appear at right angles to the direction of the applied stress.

Ozone attacks the double bonds in the rubber, causing it to break. 1. eplace with ozone-resistant rubber material.
2. Protect the surface.
Blistering (bubbles)

Slightly cracked areas appear on the surface, and some parts may swell.

 High-pressure gas enters the rubber, and when it expands (as the pressure is released), it damages the rubber. 1. Allow sufficient time when releasing pressure.
2. Use hard rubber or high-modulus rubber.
3. Use a compound formulated to resist blistering.
Twisting

Damage caused by twisting can be observed on the O-ring cross-section.

1. One part of the O-ring is fixed, while another part bends and twists.
2. Uneven load.
3. Uneven lubrication 		1. Improve lubrication.
2. Narrow the clearance.
Twisting Damage due to improper installation

A portion of the seal is shaved off, or part of the seal protrudes from the groove and is tightly pinched.

1. Sharp edges or insufficient chamfering on the mating surface.
2. The seal is too small for the rod diameter.
3. The seal is too large for the piston diameter. 		1. Ensure proper chamfering and emove sharp edges.
2. Adjust the seal size to match the groove.
Abnormal wear on marked areas

Only the marked area shows significant wear.

 The mark acts as a kind of foreign substance, causing localized wear. 1. Do not apply marks.
2. Use a colored O-ring instead.