Author: Site Editor Publish Time: 2026-10-22 Origin: Site
An O-ring is only as good as the groove it sits in. Get the gland geometry wrong and even the best compound will leak, extrude, or twist. This guide covers the four numbers that matter: squeeze, stretch, gland fill, and backup rings.
Squeeze is how much the O-ring is compressed in the groove, usually 15-30% for static seals and 10-20% for dynamic. Too little and it leaks; too much and it damages the ring or needs excessive closing force.
The O-ring should stretch slightly onto the male member – typically up to 5% for static and less for dynamic. Over-stretch thins the cross-section and reduces service life.
With no pressure, the O-ring should fill about 60-90% of the gland volume so it has room to expand when pressurized. Overfill causes pinch; underfill lets it wander.
Above roughly 1500 psi (static) or 600 psi (dynamic), the ring extrudes into the clearance gap. A backup ring (often PTFE or nylon) behind the O-ring prevents extrusion.
| Parameter | Static | Dynamic |
|---|---|---|
| Squeeze | 15-30% | 10-20% |
| Surface finish | 32-63 RA | 8-16 RA |
| Lubrication | Optional | Required |
Start from the standard that matches your drawing. Our tools cover the common ones:
Start at 20-25% for static and 15% for dynamic, then adjust for hardness and pressure.
Whenever system pressure exceeds about 1500 psi static or 600 psi dynamic, or the clearance gap is large.
No. The groove is sized to a specific cross-section; mixing sizes changes squeeze and fill.
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