A static seal uses an O-ring with a 3.55 mm cord diameter at 20% squeeze. Does the ring fit the groove?
Depth and width each do a different job
Groove depth follows from the squeeze: depth = cord diameter × (1 − squeeze%). Static seals typically use 15-30% (default 20%); dynamic seals use less, 10-16% (default 12%), to limit friction and wear. Groove width, across the squeeze direction, gives room for the displaced volume and thermal expansion: width = cord diameter × width factor, typically 1.3-1.4×.
Worked example: 3.55 mm cord, 20% squeeze
With a width factor of 1.4, this gives a depth of 3.55 × 0.8 = 2.84 mm and a width of 3.55 × 1.4 = 4.97 mm. The O-ring's cross-section is π·3.55²/4 ≈ 9.90 mm²; the groove's cross-section is 2.84 × 4.97 ≈ 14.11 mm². The fill comes out to about 70% — a nominal estimate, not proof of adequate swelling or tolerance margin. Check worst-case gland fill with dimensional tolerances, swelling and thermal expansion.
When the ring doesn't fit
Take the same cord diameter with 30% squeeze and a tight 1.1 width factor: depth 2.485 mm, width 3.905 mm, fill ≈ 102%. That isn't a tight margin — it's a physically invalid geometry: the O-ring's nominal cross-section doesn't fit in the groove, before swelling, tolerances or thermal expansion are even factored in. Mechify's `overfilled` flag catches exactly this case; checking only whether the squeeze percentage fell in the recommended range wasn't enough to catch it.
Assumptions and applicability limits
ISO 3601-2 publishes detailed gland tables per application and cord diameter; this tool calculates from the underlying design rule instead. That's indicative for a first design. Check the final groove dimensions against ISO 3601-2 or a manufacturer design guide (Parker, Trelleborg) before production, especially for dynamic seals. Also check fluid compatibility, extrusion gap, pressure and temperature.