When it comes to O-Rings, it’s a common misconception that tighter always means better. After all, a tighter seal must mean fewer leaks, right?
Not exactly.
O-Rings are essential components in everything from hydraulic cylinders to medical devices, but their effectiveness hinges on precise compression—what’s known as O-Ring squeeze. Too much squeeze can actually cause seals to fail faster, while too little can leave gaps and lead to leaks.
Whether you're designing a new system or troubleshooting premature wear, understanding how O-Ring squeeze works—and why proper groove dimensions, application type, fluid compatibility, and material selection are critical—is the key to long-lasting, leak-free performance.
What Is O-Ring Squeeze?
O-Ring squeeze refers to the amount a ring is compressed in its groove once installed between two mating surfaces. When compressed, the O-Ring deforms to fill the space between these surfaces, creating a tight seal that blocks fluid or gas from escaping.
There are two primary types of squeeze:
- Radial Squeeze: This happens when the O-Ring is compressed between inner and outer diameters, as seen in dynamic applications like rotating shafts or hydraulic pistons.
- Axial Squeeze: Here, the O-Ring is compressed between two flat surfaces, as in static applications like flanged connections or lid seals.
The amount of squeeze is typically expressed as a percentage of the O-Ring's cross-sectional diameter. The key is to apply enough compression to form an effective seal—without distorting or overstressing the ring.
Why Too Much Squeeze Is a Problem
While some squeeze is necessary for sealing, too much of it can be harmful. Excessive squeeze can cause:
- Deformation: The O-Ring may bulge or extrude out of its groove, especially under pressure.
- Friction and Wear: Increased compression causes higher friction during dynamic movement, which leads to heat buildup and faster material degradation.
- Compression Set: Over-compressed O-Rings are more prone to permanent flattening, reducing their ability to rebound and reseal after deformation.
- Material Breakdown: Under excessive force, even chemically compatible materials can crack, tear, or degrade prematurely—especially in aggressive or high-temperature environments.
It’s also worth noting that over-compression can make installation much more difficult and increases the risk of nicking or tearing the O-Ring during assembly.
How to Get the Right Amount of Squeeze
Getting squeeze right starts with proper gland (groove) design. Each application—static or dynamic—has an ideal squeeze range to ensure performance without premature wear:
- Static Seals: Typically require 10% to 30% squeeze, depending on pressure and sealing surface quality.
- Dynamic Seals: Perform best with 8% to 15% squeeze to minimize friction and prolong service life.
Other factors to consider include:
- Thermal expansion: As materials heat up, they expand—potentially increasing squeeze beyond safe limits.
- Pressure fluctuations: Variable pressures can cause momentary extrusion or distortion if the groove isn't properly designed.
- Fluid swell: Some sealing materials can absorb system fluids, increasing volume and potentially leading to over-compression.
Designing grooves to the right depth and width ensures consistent squeeze and helps the O-Ring stay seated under all operating conditions.
What Is Gland Fill and Why Does It Matter?
Alongside squeeze, gland fill is a critical but often overlooked factor. Gland fill refers to the volume of the groove that is occupied by the O-Ring once compressed. It’s possible to have the correct squeeze percentage but still have too much gland fill, which can cause the O-Ring to extrude or deform.
As a general rule:
- Keep gland fill under 85% for dynamic applications.
- For static applications, up to 90% may be acceptable depending on temperature and pressure.
Too little fill, on the other hand, can lead to O-Ring instability, resulting in twisting, rolling, or failure under vacuum or fluctuating pressure.
The Role of Pressure and Vacuum in O-Ring Squeeze
Different operating environments demand different squeeze strategies.
- In high-pressure systems, excessive squeeze can combine with pressure loads to force the O-Ring into extrusion, especially without a backup ring. It may also amplify friction and wear in dynamic seals.
- In vacuum applications, more squeeze is often needed to ensure that no air is drawn in around the seal. However, materials must also withstand potential outgassing and environmental stressors.
Knowing the pressure conditions of your application helps determine not just squeeze, but material selection, groove geometry, and whether additional components like backup rings are needed.
Temperature Effects on Compression and Seal Performance
Temperature has a direct effect on how O-Rings behave:
- High temperatures can cause O-Rings to swell, increasing squeeze to potentially damaging levels.
- Low temperatures may cause the material to harden or become brittle, reducing squeeze effectiveness and preventing the O-Ring from conforming to its sealing surfaces.
Always choose a material with a thermal range suitable for your environment, and adjust groove and squeeze tolerances accordingly. Silicone, for example, performs well in extreme cold but has poor resistance to wear. Viton® holds up well under high heat and pressure.
How Fluid Compatibility Affects Squeeze Performance
It’s not just the shape and size of the O-Ring that matters—what it’s sealing against is equally important. Certain fluids, especially aggressive chemicals or oils, can cause materials to swell, shrink, or harden over time.
Even a well-designed seal with optimal squeeze can fail prematurely if the O-Ring material absorbs fluid and changes dimension or flexibility. This is especially common in fuel systems, refrigerants, or chemical process lines.
Refer to chemical compatibility charts during material selection to minimize unexpected performance issues and material degradation.
Compression Set: A Common (and Costly) Failure Mode
Compression set is one of the most frequent causes of long-term seal failure. It happens when an O-Ring becomes permanently deformed and fails to return to its original shape after being compressed. When this happens, the sealing force weakens, and the system becomes vulnerable to leaks.
Causes of compression set include:
- Excessive squeeze
- High temperatures
- Incompatible fluids
- Long-term static load without pressure cycling
To reduce the risk:
- Select materials with good compression set resistance (like Viton® or EPDM).
- Avoid over-compressing.
- Allow for proper relaxation time when possible.
Inspect O-Rings during maintenance cycles for signs of flattening or brittleness, and replace as needed.
Material Matters: Tolerance to Squeeze
Not all O-Ring materials respond to squeeze the same way. Material flexibility, thermal stability, and chemical resistance all play a role in how well a seal performs under pressure. Here's a quick guide:
Using the right material not only ensures chemical compatibility but also helps manage the stress that comes from long-term compression—especially in challenging environments.
Tips for Preventing Installation Damage
Even if you’ve selected the right size and material, poor installation can ruin a seal before it’s even put to use. Avoid these common mistakes:
✅ Do:
- Lubricate the O-Ring before installation to reduce friction and prevent tearing.
- Use proper installation tools like seal picks or tapered mandrels designed for soft seals.
- Check alignment of components to avoid rolling, twisting, or pinching the seal during closure.
❌ Don’t:
- Stretch the O-Ring too far, which can permanently deform it or weaken its structure.
- Install dry, especially in dynamic applications where motion or pressure is involved.
- Force seals with sharp tools, which can easily cause nicks or scratches that compromise integrity.
A little care during installation can dramatically improve performance and extend seal life.
The Bottom Line
More squeeze doesn’t mean more sealing power. In fact, too much compression can shorten seal life, cause leaks, and lead to expensive downtime.
Getting the most out of your O-Rings means understanding the right balance of squeeze, selecting the correct materials, and designing grooves that support long-term performance.
At Rocket Seals, we help customers do just that. Our experts can guide you to the right O-Ring for your system—whether it's standard, specialty, or custom.
Need Help Choosing the Right O-Ring?
We stock a wide range of materials and sizes and offer expert support to ensure you get the best seal for your application.
Contact Rocket Seals today to speak with our team or request a quote.