BIZOMAT MAKEOS · Engineering
O-Ring Groove Design (Depth, Width, Bore and Extrusion Gap)
What groove depth and width give my target squeeze and fill for this O-ring, what mating diameter does that set, and is the extrusion gap small enough?
Design of a radial O-ring gland (piston or rod): stretch of the ring on the groove diameter and the reduced cross-section, groove depth for your target squeeze, groove width for your target fill, the mating bore or rod diameter that results, and a check of the depth and width you actually choose for squeeze, fill and stretch against your limits (as the O-ring gland tool), with the extrusion gap against your allowable for the pressure.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Gland | choice | Whether the groove is on the moving inner part (piston) or in the housing (rod). |
| O-ring inside diameter | mm | Inside diameter of the O-ring. |
| O-ring cross-section | mm | Cross-section diameter of the O-ring. |
| Groove diameter (bottom for piston, outer for rod) | mm | For a piston, the diameter at the bottom of the groove; for a rod, the outer diameter of the groove. |
| Target squeeze | % | Squeeze you design to. |
| Target fill | % | Share of the groove area the ring fills, designed to. |
| Groove depth chosen (0 = use the design value) | mm | Groove depth on the drawing (0 to use the design value). |
| Groove width chosen (0 = use the design value) | mm | Groove width on the drawing (0 to use the design value). |
| Your limits | ||
| Smallest squeeze | % | Smallest squeeze you accept (for the duty; from the seal maker). |
| Largest squeeze | % | Largest squeeze you accept. |
| Largest fill | % | Largest fill you accept (room for swell and heat). |
| Largest stretch (piston) or compression (rod) | % | Largest stretch of the ring on a piston groove, or diametral compression in a rod groove. |
| Radial extrusion gap | mm | Radial clearance between the parts at the seal. |
| Largest gap for the pressure and hardness | mm | Largest clearance for the pressure and ring hardness (from the seal maker). |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Gland
- What it is
- Whether the O-ring sits in a groove on the inner part and seals against a bore (piston), or in a groove in the housing and seals against a rod (rod).
- Units and format
- Choose one of 2 options from the list: Piston (groove on the inner part, seals on a bore); Rod (groove in the housing, seals on a rod).
- Example
- The form opens with “Piston (groove on the inner part, seals on a bore)” selected as a worked example. Choose the option that matches your case.
- Get it right
- It changes the meaning of the groove diameter and whether the ring is stretched or compressed when fitted.
What this means: O-ring inside diameter
- What it is
- The inside diameter of the O-ring as made, from the size table or the seal maker’s data.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 2000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 47.22 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Use the nominal inside diameter, not the diameter of the groove it fits.
What this means: O-ring cross-section
- What it is
- The thickness of the O-ring cord, the diameter of its round cross-section.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 20 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2.62 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger cross-section needs a deeper and wider groove.
- Get it right
- Use the nominal cross-section from the size table, not a measured flattened ring.
What this means: Groove diameter (bottom for piston, outer for r…
- What it is
- For a piston gland, the diameter at the bottom of the groove; for a rod gland, the outer diameter of the groove in the housing.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 2000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 48 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Check the gland choice first: this is the groove bottom for a piston and the groove outside for a rod.
What this means: Target squeeze
- What it is
- The squeeze you design to: how much the groove depth compresses the ring cross-section, as a share of the cross-section.
- Units and format
- Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 5% to 40%. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 20% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- More squeeze gives a shallower design groove.
- Get it right
- Type the percentage itself. Choose it within the seal maker’s range for your duty.
What this means: Target fill
- What it is
- The share of the groove cross-section area the ring is designed to fill, leaving room for swelling and heat.
- Units and format
- Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 40% to 95%. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 75% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A higher fill target gives a narrower design groove.
- Get it right
- Type the percentage itself.
What this means: Groove depth chosen (0 = use the design value)
- What it is
- The groove depth on your drawing, from the groove bottom to the sealing surface it faces.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 20 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2.1 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A deeper groove gives less squeeze and less fill.
- Get it right
- Use 0 to check the design depth the tool works out; enter your drawing value to check it instead.
What this means: Groove width chosen (0 = use the design value)
- What it is
- The groove width on your drawing, measured along the axis between the groove side walls.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 40 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 3.6 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A wider groove gives less fill.
- Get it right
- Use 0 to check the design width; enter your drawing value to check it instead.
Your limits
What this means: Smallest squeeze
- What it is
- The smallest squeeze you accept for a reliable seal, from the seal maker for the duty.
- Units and format
- Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 0% to 40%. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 15% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Type the percentage itself; it must be below the largest squeeze.
What this means: Largest squeeze
- What it is
- The largest squeeze you accept before the ring is overcompressed, from the seal maker for the duty.
- Units and format
- Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 1% to 50%. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 30% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Dynamic seals usually allow less squeeze than static seals.
What this means: Largest fill
- What it is
- The largest share of the groove area the ring may fill, leaving room for swell and thermal expansion.
- Units and format
- Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 40% to 100%. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 85% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Allow for the swell of the ring material in your fluid.
What this means: Largest stretch (piston) or compression (rod)
- What it is
- The largest change you accept in the ring size when fitted: stretch over the groove bottom for a piston, or diametral compression in the housing for a rod.
- Units and format
- Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 0% to 20%. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 5% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Type the percentage itself; take the limit from the seal maker.
What this means: Radial extrusion gap
- What it is
- The radial clearance between the two parts at the seal, the gap the ring could be pushed into under pressure.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 2 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.1 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Radial clearance is half the diametral clearance; use the largest value the part tolerances allow.
What this means: Largest gap for the pressure and hardness
- What it is
- The largest extrusion gap the ring can bridge at your pressure and ring hardness, from the seal maker’s chart.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 2 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.15 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Use the same radial basis as the gap you entered.
Method and formulas
- Piston stretch = (groove diameter − ring ID) ÷ ring ID; rod compression from the ring OD; stretched cross-section = cs ÷ √(1 + stretch) (as the O-ring gland tool).
- Depth = cs′ (1 − squeeze); width = π cs′² ÷ 4 ÷ (depth × fill).
- Mating bore (piston) = groove diameter + 2 × depth; mating rod (rod) = groove diameter − 2 × depth.
- At the chosen groove: squeeze = (cs′ − depth) ÷ cs′; fill = π cs′² ÷ 4 ÷ (depth × width).
- Example: the ring stretches 1.6518%; 2.0789 × 3.4016 mm gives the target, and the chosen groove gives 19.188% squeeze and 70.154% fill.
Limitations
- Nominal dimensions; check squeeze and fill at the tolerance extremes too.
- Static or slow dynamic seals; high-speed and rotary seals need different glands.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Design a gland for a standard O-ring
- Check a drawn gland before machining
- Find the clearance a pressure allows
Who it is for
- Design engineers
- Hydraulic engineers
- Sealing engineers
What you get
- Stretch and stretched cross-section
- Design depth, width and mating diameter
- Squeeze, fill, stretch and gap checks at the chosen groove
Interpreting the result
- If the extrusion gap is too large for the pressure, fit a back-up ring rather than tightening the fit.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2591–2610. Topic reference; no source tables or recommended settings are reproduced.
- ISO 3601-2 Fluid power systems — O-rings — Housing dimensions for general applications
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Open the O-Ring Groove Design (Depth, Width, Bore and Extrusion Gap) calculator