O-Ring Groove Design
Designing for Reliable Compression
Correct groove geometry is as important as selecting the right elastomer. A properly dimensioned groove delivers consistent squeeze, limits extrusion, and maintains seal force over temperature cycles and wear. Use this guide alongside the O-Ring Size Chart and Material Selection Guide when developing new hardware or reviewing field failures.
Garlast engineers routinely review customer groove drawings for AS568 and metric housings. Share your groove ID, groove width, depth, and tolerance stack-up for a fit check before prototyping or production release.
Core Groove Parameters
- Groove inside diameter (ID): Controls O-ring stretch during installation and retained seal stress.
- Groove outside diameter (OD): Defines compression for face seals and gland volume for radial seals.
- Groove width: Must accommodate cross-section swell, thermal expansion, and tolerance variation.
- Groove depth: Sets squeeze percentage relative to the O-ring cross-section (CS).
- Surface finish: Target Ra 16–32 µin (0.4–0.8 µm) on sealing surfaces; break sharp edges.
- Lead-in chamfers: Ease assembly without cutting or twisting the seal.
Recommended Squeeze & Stretch Ranges
| Application | Squeeze (%) | Stretch (%) | Notes |
|---|---|---|---|
| Static — face seal | 18–30 | 0–3 | Higher squeeze acceptable; verify compression set of elastomer. |
| Static — radial (rod) | 15–25 | 0–5 | Limit stretch on small cross-sections to avoid stress concentration. |
| Static — radial (piston) | 15–25 | 2–5 | Ensure groove fill stays below ~85% after media swell. |
| Dynamic — reciprocating | 10–18 | 2–5 | Lower squeeze reduces friction and heat build-up. |
| Dynamic — rotary (limited) | 8–13 | 2–5 | Requires excellent surface finish and compatible lubrication. |
| Low-temperature service | +2–4% vs standard | Minimize | Compensate for elastomer stiffening and shrinkage at cold start. |
Common Design Considerations
Gland Volume & Swell
Reserve 10–15% void volume in the groove for thermal expansion and fluid swell, especially with NBR in oil or FFKM in aggressive solvents.
Extrusion Gaps
At pressures above ~1,500 psi (10 MPa), reduce extrusion gap or add backup rings. Soft compounds extrude before harder FFKM grades.
Pressure Direction
Orient the seal so system pressure energizes the seal against the low-clearance side of the groove whenever possible.
Tolerance Stack-Up
Evaluate worst-case squeeze using minimum CS tolerance and maximum groove depth. Confirm sealability at both extremes.
