Gland depth, groove width and clearance for static face seals and moving seals.
An O-ring seals because the groove squeezes it. Too little squeeze leaks at low pressure. Too much raises friction and wear on a moving seal. The tables give gland depth, groove width and clearance for the five AS568 cross sections. They are based on the Parker O-Ring Handbook's design charts for industrial use.
For a groove cut in a flat face, sealing against a flat cover. Inches, with mm in brackets. L = gland depth, G = groove width.
| W | Gland depth L | Squeeze | G, liquids | G, vacuum and gases | Groove radius |
|---|---|---|---|---|---|
| .070 (1.78) | .050–.054 (1.27–1.37) | 19–32% | .101–.107 (2.57–2.72) | .084–.089 (2.13–2.26) | .005–.015 |
| .103 (2.62) | .074–.080 (1.88–2.03) | 20–30% | .136–.142 (3.45–3.61) | .120–.125 (3.05–3.17) | .005–.015 |
| .139 (3.53) | .101–.107 (2.57–2.72) | 20–30% | .177–.187 (4.50–4.75) | .158–.164 (4.01–4.17) | .010–.025 |
| .210 (5.33) | .152–.162 (3.86–4.11) | 21–30% | .270–.290 (6.86–7.37) | .239–.244 (6.07–6.20) | .020–.035 |
| .275 (6.99) | .201–.211 (5.11–5.36) | 21–29% | .342–.362 (8.69–9.19) | .309–.314 (7.85–7.98) | .020–.035 |
5 rows
No back-up ring. Inches, with mm in brackets. E = diametral clearance, the total gap between the moving parts.
| W | Gland depth L | Squeeze | E, clearance | G, no back-up | Groove radius |
|---|---|---|---|---|---|
| .070 (1.78) | .055–.057 (1.40–1.45) | 15–25% | .002–.005 (.05–.13) | .093–.098 (2.36–2.49) | .005–.015 |
| .103 (2.62) | .088–.090 (2.24–2.29) | 10–17% | .002–.005 (.05–.13) | .140–.145 (3.56–3.68) | .005–.015 |
| .139 (3.53) | .121–.123 (3.07–3.12) | 9–16% | .003–.006 (.08–.15) | .187–.192 (4.75–4.88) | .010–.025 |
| .210 (5.33) | .185–.188 (4.70–4.78) | 8–14% | .003–.006 (.08–.15) | .281–.286 (7.14–7.26) | .020–.035 |
| .275 (6.99) | .237–.240 (6.02–6.10) | 11–16% | .004–.007 (.10–.18) | .375–.380 (9.53–9.65) | .020–.035 |
5 rows
On a radial seal, the depth you cut is less than L by half the clearance: groove depth = L − E ÷ 2. Other charts swap these letters, so check the drawing's key.
Liquid grooves are wider because a seal can swell a little in the fluid. Vacuum grooves are narrower, to reduce trapped gas.
Pressure direction sets the groove diameter. With pressure from inside, the ring should rest on the groove's outer wall, so the groove OD is the key size. With pressure from outside, the groove ID is. On a rectangular groove, make the inside corner radii at least three times W.
Moving seals use less squeeze than static ones, to limit friction and the rolling that causes spiral failure. A back-up ring needs a wider groove, so take that width from the handbook. Rotary seals have a separate, stricter design and are not covered here.
The ring has W = 0.139 in (3.53 mm). A reciprocating piston with L = 0.122 in gives:
Squeeze = (0.139 − 0.122) ÷ 0.139 = 12%
The same ring in a face groove with L = 0.104 in gives 25%. That is the difference between a seal that slides and one that must not move. Ring sizes come from the O-ring size chart, and stretch on the piston reduces W, so more than a few percent needs correcting.
High pressure pushes rubber into the clearance gap. Keep the gap small, within the E column at full pressure. The bore can grow under load, so check the gap under pressure, not only at the bench. The hydraulic pressure calculator gives the working pressure.
Parker says to investigate back-up rings above 1,500 psi (103.5 bar) for all seal types. Pulsing pressure can call for them at lower pressure, because the gap opens and closes. The gap tolerance comes from the shaft and bore fits, so check them against the ISO fits and tolerances chart.
Parker's limits for static seals are 32 µin (0.8 µm) on the sealing surface and 16 µin (0.4 µm) for face-type gas seals. The dynamic chart shows 16 µin on the moving surface. Below about 5 µin a rod holds no oil and runs dry. The direction of tool marks matters as much as the number, so see what surface roughness measures.
For a seal that protects people or equipment, confirm the groove with your seal supplier and test it.
By O.E. — Partner, chairman of the board and CEO of a metal products manufacturer for 21 years; the company exports to 45 countries.
Drafted with AI assistance; calculations checked against primary sources and tested with the site's own code. About FlowUtil
Last reviewed
Classification: Maker design charts for industrial glands
Sources
Parker O-Ring Handbook ORD 5700 — Design Chart 4-3 and Design Chart 5-2
Parker Hannifin
AS568 — O-ring sizes; AS5857 and AS4716 — gland design
SAE International
The tables copy the Parker design charts, in inches with millimetres converted at 25.4. AS568 sets ring sizes only; groove design is in other documents. Metric-only cross sections are left out, because the handbook has no chart for them.
The gland must squeeze the O-ring by the right amount and leave room for it to deform without extruding. Gland depth sets the squeeze, groove width sets the fill, and the clearance gap limits extrusion.
Classification: Stable (mature standard)
Gland design principles are stable, but the exact dimensions depend on the application type, pressure and compound. Confirm with your seal supplier for critical seals.
Inches, with millimetres in brackets; squeeze in percent of the cross section.
Go deeper with FlowUtil guides that explain the concepts behind this reference table.
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