Air leaks, jerky starts, and short seal life waste money. I fix many of these issues by switching one small part: the quad ring.
A quad ring—also called an X-ring—is a four-lobed elastomer seal that provides two sealing lines with lower squeeze than a round O-ring. It resists twisting, reduces friction, holds lubricant between its lobes, and improves sealing in static and dynamic applications.
I use quad rings in cylinders, valves, and rotary actuators when O-rings spiral, glaze, or need too much clamp force. The design looks simple, but the benefits are big.
How does a quad ring work?
The cross-section looks like an “X.” Each side forms a lobe. When you install it in a groove, the opposing lobes create two contact lines1 on each sealing surface. Those lines seal at lower squeeze than an O-ring, so friction drops. The valleys between the lobes hold lubricant2, which further cuts wear and stick-slip. The X shape also resists rolling and spiraling3 during reciprocating motion.
✅ Two sealing lines = tight seal at low squeeze
✅ Lube pockets = smoother starts and longer life
✅ Anti-twist geometry = fewer spiral failures
Quad ring vs. O-ring: what’s the difference?
| Feature | Quad ring (X-ring) | O-ring |
|---|---|---|
| Sealing contact | Two lines per surface | One line per surface |
| Required squeeze (dynamic) | Lower for same seal | Higher for same seal |
| Friction & breakaway | Lower; smoother motion | Higher; more stick-slip risk |
| Twist/spiral resistance | Very good due to X geometry | Can twist/spiral in dynamic duty |
| Lube retention | Built-in valleys | None |
| Groove compatibility | Often fits O-ring glands* | Standardized |
| Best use cases | Low-pressure air, high cycle, precision motion | Broad, general-purpose sealing |
* Many X-rings drop into standard O-ring glands, but I still verify squeeze, gland fill, and corner radii before sign-off.
Where should I use quad rings?
I reach for quad rings4 when the system needs low friction5, stable motion, and leak-free performance6 at modest pressures.
- Pneumatic cylinders: piston and rod seals to reduce stick-slip at start-up
- Spool valves & mini-actuators: low breakaway, high cycle life
- Vacuum tools: better sealing lines, less permeation risk
- Slow rotary or oscillating shafts: reduced drag vs. O-rings
- Static joints with limited clamp force: reliable seal without over-compression
I still use O-rings where standards, cost, or groove legacy drive the choice. For harsh extrusion gaps or high pressure spikes, I may add backup rings7 or choose a different lip profile.
Materials and hardness I recommend
The material choice follows media and temperature. Then I set hardness to balance squeeze and wear.
| Material | Typical Shore A8 | Temperature (°C) | Strengths | Avoid when |
|---|---|---|---|---|
| NBR (Nitrile) | 60–80 | −30 to +100 | Great for lubricated air; cost-effective | Heavy ozone/UV, high heat |
| HNBR | 70–85 | −30 to +140 | Better heat/ozone than NBR | Higher cost |
| EPDM | 60–80 | −40 to +130 | Steam/water, ozone, outdoor | Oils/fuels |
| VMQ (Silicone) | 50–70 | −60 to +200 | Very low μ, cold starts | Abrasion/tear |
| FKM | 70–80 | −20 to +200 | Hot air, chemicals/solvents | Very low ambient starts |
| PU (Polyurethane) | 85–95 | −30 to +110 | High wear & extrusion control | Hot water/steam (polyester grades) |
Tips I use daily:
- Pneumatic dynamic duty → 60–70A for low breakaway when hardware is tight.
- Dusty or side-loaded duty → 80–90A or PU for lip strength.
- Hot ovens or vapor exposure → FKM for shape retention.
Sizing and groove guidance (quick facts)
Quad rings are available in AS568 dash sizes, matching common O-ring IDs and cross-sections (e.g., 1.78, 2.62, 3.53, 5.33, 6.99 mm). Most of my projects reuse existing O-ring glands with small adjustments.
Targets I check before release (general pneumatic guidance):
- Dynamic squeeze9: typically 5–12% for X-rings (lower than O-rings)
- Static squeeze: typically 12–25%
- Gland fill: ≤85% at max swell for dynamic; ≤90% static
- Surface finish10: rods Ra 0.2–0.4 µm, bores Ra 0.4–0.8 µm
- Lead-in chamfers: 15–20°, polished, to avoid nicking
If the groove is wide, I add anti-extrusion backups or move to a harder compound. For very tight friction targets, I consider PTFE-filled elastomers11 or PTFE-lip + elastomer-energized designs.
Common failures—and how a quad ring helps
| Symptom | Typical cause with O-rings | Quad ring advantage12 | My extra fix if needed |
|---|---|---|---|
| Stick-slip at start | Too much squeeze, high μ | Lower squeeze for same seal | Softer durometer; micro-lube |
| Spiral failure | Ring rolls/twists in groove | X geometry resists twisting | Correct stretch; guided hardware |
| Glazing/heat | Friction from over-squeeze | Lower drag | Polish rod; align bushings |
| Micro-leaks | Low pressure, rough finish | Two seal lines improve contact | Improve finish; verify squeeze |
| Nibbling/extrusion | Large gaps, pulses | Better stability | Add backups; tighten clearances |
When is a quad ring not ideal?
- Very high-speed rotation: use dedicated rotary lip seals.
- Large extrusion gaps or high spikes: use backups or switch profile.
- Extreme vacuum with loose hardware: consider energized PTFE lips.
- Tight cost with huge volumes: O-rings may win if performance is acceptable.
Quick selection checklist
- Media and temperature confirmed?
- Dynamic or static duty? Required breakaway force target known?
- Hardware clearances and surface finish in spec?
- Choose material and Shore A for the environment.
- Verify squeeze and gland fill with the actual dash size.
- Consider X-ring first for low-pressure air and high cycle life.
- Pilot test for leak rate and friction before locking the BOM.
Need help picking the right quad ring?
Send me the groove drawing, media, and temperature. I will recommend compound, hardness, and dash size. I can supply samples and full inspection reports fast from my factory.
Contact: info@rubberandseal.com · Website: www.rubberandseal.com
Brand: Julong Rubber · Country: China · Products: Rubber seals & custom molded parts
Conclusion
A quad ring is an X-shaped upgrade to the O-ring. It seals better at lower squeeze, runs smoother, and resists twisting. That is why I use it in pneumatic cylinders, valves, and vacuum tools.
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Explore how two contact lines enhance sealing efficiency and reduce friction in various applications. ↩
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Learn how designs that retain lubricant can significantly reduce wear and enhance the lifespan of seals. ↩
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Discover the engineering behind seals that prevent rolling and spiraling, ensuring reliable performance. ↩
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Learn about quad rings, their unique features, and how they compare to traditional O-rings for sealing solutions. ↩
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Understand the importance of low friction in seals for smoother operation and reduced wear. ↩
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Explore the key factors that ensure seals maintain leak-free performance in various applications. ↩
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Find out when and why backup rings are essential for preventing seal failure in critical applications. ↩
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Discover how Shore A hardness ratings influence the performance and durability of sealing materials. ↩
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Understanding dynamic squeeze is crucial for optimal seal performance; explore this link for detailed guidelines. ↩
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Learn how surface finish impacts seal integrity and performance, ensuring long-lasting functionality. ↩
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Explore the unique properties of PTFE-filled elastomers and how they can improve sealing in challenging environments. ↩
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Discover the benefits of quad rings, which can enhance sealing performance and reduce common failures. ↩
