A Beginner's Guide to O-ring Troubleshooting | DCW

A Beginner’s Guide to O-ring Troubleshooting

O-Rings, usually manufactured from PTFE, are highly useful sealing tools, but they are not perfect. When they fail, it’s generally a result of the negative effects of various environmental conditions acting together. The combinations of stress on the O-Ring can be complicated and difficult to assess. Therefore, it is essential to evaluate the O-Ring composition and size in the actual service environment.

This guide will help you identify common causes and models of O-ring failures, along with their maintenance techniques. 

Common O-ring Failure Causes

An O-ring is a donut-shaped tube that is intended to be seated in a groove and compressed between two or more elements, creating a seal at the interface. Although many fluid-power systems work quite well with this simple setup, successful working still necessitates detailed planning, selection, and installation techniques.

O-rings usually fail in their intended applications as a result of the negative effects of various environmental conditions working together. According to experts, these are the most common reasons for O-ring failure:

  • Weak gland design that permits excessive or insufficient compression
  • Insufficient O-ring lubrication
  • Insufficient space for displacement during compression
  • Faulty O-ring installation
  • No compatibility between the O-ring elastomer and the environment it must contact

Common O-ring Failure Models and How to Fix Them 

Several O-rings placed next to a paperclip
Source: Dechengwang

Here are some common types of o-ring failures, what cause those failures, and solutions to fix them.

Abrasion

Abrasion can be caused by the surface of the ring coming in excessive contact with its housing leading to unnecessary generation of friction. This is mostly noted in dynamic functions. Abrasion can be identified by grazing on one of the flat sides of the o-ring which lies parallel to the direction of movement. With time, these tiny cuts can develop into deeper lacerations which allow for even more abrasive material to come in contact with the ring. 

Causes

  • Poor surface finishing in dynamic contact with the O-Ring. The surface finish could be too smooth, which prevents proper lubrication since the surface cannot hold oil, or it may be excessively rough, functioning as an abrasive.
  • Extreme temperatures
  • Insufficient lubrication is provided by the system fluid. 
  • System fluid contamination by abrasive particles.

Solution

  • Using the proper system fluid to offer sufficient lubrication
  • Applying the right surface finish.
  • Employing internally lubricated O-Rings to minimize wear and friction.
  • Inspecting the fluid for contaminants, removing the source, and adding filters.
  • Changing to an O-Ring made of a more abrasion-resistant substance.
  • Out-gassing

Out-gassing

Usually, there are no indicators that show out-gassing. In most severe cases, you can see shrinkage of the seal. 

Causes

High vacuum conditions can cause the seal material or by-products of chemical degradation trapped in the system to be released causing this kind of failure. This is caused by improper curing or low hardness of the seal material. 

Solution

Materials that are made of pure polymers and free of volatile substances like thermoplastics and waxes, result in minimal outgassing. Using materials with the appropriate temperature rating for the application also contributes to minimizing outgassing.

Extrusion and Nibbling

Another primary cause for O-ring seal failure in dynamic applications is extrusion and nibbling. This type of failure is generally found in static applications that undergo high-pressure pulsing from time to time, which causes a clearance gap of the mating fringes to open and close. It will result in trapping the O-ring between mating surfaces. 

Causes

  • High-pressure outbursts and high-pressure levels that are above the system design. At extremely high pressure, o-rings can experience failure to function properly. 
  • Too many clearances.
  • Inconsistent clearance gaps brought on by electricity.
  • Material for O-Rings is overly flexible.
  • Corrosion of O-Ring material from the system fluid, including swelling, shrinking, bending, etc.
  • Increased clearance gaps as a result of high system pressure.
  • Improper O-Ring gland machining (sharp edges).
  • The installed O-ring is too large, resulting in excessive groove filling.

Solution

  • Use back-up devices to supplement the o-ring function.
  • Increase the rigidity of metal parts
  • Decrease clearance by reducing machining tolerance
  • Use the right material for o-rings and make sure that it is compatible with the system
  • Choose PTFE o-rings to prevent corrosion.
  • Reduce the sharp edges in glands and make sure it has an appropriate design.
  • Use an o-ring of the right size and employ a seal of a harder material.
  • Chemical Degradation

Chemical Degradation

If the ring material is incompatible with the thermal and/or chemical environment, it can develop cracks, lacerations, and blisters. In some circumstances, only physical property measurements can indicate the degradation.

Causes

Certain elastomers will react with specific substances. Most frequently, this causes a rise in cross-link density, which leads to a hard, brittle material with a diminished ability to generate a response force.

It is also possible for chains to split, which would weaken them. It is common for cross-link density to occasionally decrease, resulting in a softer, chunkier material that loses its original shape and integrity.

Solution

You need the proper material for chemical resistance in the application. Chemical deterioration happens more quickly when the O-ring is subjected to extreme pressure and temperatures. Most manufacturers prefer PTFE seals because they can endure high temperatures and pressures. 

Compression Set

An efficiently functioning o-ring needs an uninterrupted “seal line” between the sealed surfaces. This sets up the accurate amount of compression that the seal can take. Doing so ensures seal integrity. However, when the compression between the seal lines is not proper, it will cause the ring to lose its O shape and deform. This deformation does not go away when the o-ring is removed

Causes

A compression set is typically brought on by one or more of the following situations:

  • Choosing an O-Ring material having weak compression set qualities by nature.
  • The system fluid causes the O-Ring to increase in volume.
  • Excessive compression brought on by overly tightened adjustable glands.
  • Incorrect gland design.
  • At an extremely high-temperature O-rings can harden and lose their elastic characteristics. 

Solution

You can easily fix the compression set by:

  • Using low-set materials from PTFE components manufacturers whenever possible.
  • Lowering the temperature of the system.
  • Ensure that the material of the seal is compatible with the service conditions.
  • Make sure that the o-ring is not being squeezed excessively and reduce frictional heat build-up at the sealing surface.

Explosive Decompression

Explosive decompression causes the sealing surface to be entirely ruptured, marked by deep cuts, blisters, cracks or splits in the worst scenarios. 

Causes

High-pressure gas penetrates into the polymer compound when elastomer seals are exposed to it over an extended period of time at high temperatures. The gas that is dissolved in the substance escapes from the solution and forms microscopic bubbles when the pressure outside is lowered. The gas will seep out of the substance as it expands. 

The O-ring fails when the trapped gas inside the seal expands past the material’s capacity to confine the gas bubbles and the rate of decompression and expansion is significant.

Solution

The possibility of explosive decompression (ED) damage can often be decreased by increasing the decompression period, lowering the temperature, and selecting a material, like PTFE that is ED-resistant.

Installation Damage

Imprecise installation with inadequate lubrication and incompatible ring size can lead to the development of precise grooves on the outer surface of the O-ring. This is usually observed in systems with sharp metallic parts. 

Causes

The o-ring can be damaged during installation due to sharp gland edges or machine parts. Using a ring of the wrong size or made up of a material of low hardness can also cause grooves to form in the ring. Contamination of the ring surface or inadequate lubrication also contributes to installation damage. 

Solution

Make sure all the machine components are properly cleaned before installation. Choose rings made with higher hardness elastomers and remove or cover all sharp-edged parts before they are installed. Ensure proper lubrication at the time of installation as well. 

Plasma Degradation

Discoloration, even erosion, and material loss on the seal’s surface along with a powdery residue is a crucial indicator of plasma degradation

Causes

Plasmas are made up of highly energetic ionized gases and radicals that erode the organic base of the seal’s elastomer. Thus the chemical reactivity of the plasma eats away at the seal material. Ion bombardment and incompatible seal material are the primary reasons behind this o-ring failure.

Solution

Plasma degradation is inevitable but it can be slowed down with the use of proper seal material which is plasma-compatible. It is also advisable to minimize the area of the o-ring exposed to the chemical reactions that produce plasma.

Proper Working Conditions for O-Rings 

Fuel rail O-rings
Source: Pinterest

O-ring seals are made of elastomeric circular cross-sections that are placed into an o-ring groove, specifically constructed to provide initial compression.

The cross-section diameter and durometer reading of an o-ring determine the force needed to crush it. The O-ring stretch impacts seal compression and lowers the o-sealing ring’s capacity by decreasing the cross-section.

The seal is formed by the rubber compound’s inherent resilience at zero or extremely low pressure. The diametrical squeeze can be increased to improve seal function. In applications requiring dynamic sealing at greater pressures, this increase in squeezing might not be advantageous.

The O-ring is kept in its installed position by a frictional force created by the diametrical squeezing between it and the groove. Since the rubber compound is designed to deform, it flows to the extruded gap. It entirely seals it from leaking until enough pressure is exerted to overcome the frictional forces and change the shape of the O-ring into the tiny extrusion gap. 

Note: Any excessive increase in pressure above the pressure that the O-ring’s elastomer can stand will lead to deformation causing extrusion and nibbling. 

The groove is intended to apply a starting force of 7 to 30% across one axis to the seal. There is free volume in the groove on the other axis as a result of this compressive force, which is typically perpendicular to the force being applied.

O-Ring Maintenance Tips

Three o-rings of different diameters and thickness
Source: Dechengwang

Understanding how to properly maintain an O-ring is important if you plan to use one, to prevent failure. Here are some maintenance tips that will help you keep your O-ring in shape. 

  1. Routine Change: A major part of maintenance is routinely cleaning the rings. This is especially important for O-rings that seal machinery. To prevent abrasions, you should use a soft brush to clear any debris, grit, or contaminants.
  2. Proper Storage Requirements: O-ring application and storage are both equally important. They should be kept out of direct sunlight in an airtight bag. It is always preferable to be safe than sorry because using old O-rings might have serious consequences.
  3. Proper Lubrication: O-rings used in dynamic functions and ones that require opening and closing must be properly lubricated. Improper lubrication can lead to the development of cracks. 
  4. Proper Installation: O-ring installation must be done properly because negligence might cause serious harm. Abrasions, deterioration, and flattening are just a few of the negative consequences of stretching the O-ring. These O-ring failures might result in expensive repairs since they can harm other parts that you might need to change.

Conclusion

There are always clear indicators that show failures in your O-ring applications. Even though you have easy fixes for all of them, it is better to prevent the failures in the first place. It is best to use PTFE machined parts that can endure high pressure and temperatures and don’t react to chemicals easily. You should also be wary of choosing a reliable PTFE O-ring manufacturer, such as DCW. Contact them today to learn more on the subject. 

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