BIZOMAT MAKEOS · Engineering
O-Ring Squeeze, Stretch and Gland Fill
Will this O-ring have the right squeeze, stretch and gland fill in this groove?
Squeeze, stretch (or circumferential compression), reduced cross-section and gland fill of an O-ring in a piston (male) or rod/bore (female) groove, compared with typical design ranges.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Groove location | choice | Piston (male) grooves stretch the ring; rod (female) grooves compress it circumferentially. |
| Duty | choice | Static seals tolerate more squeeze than dynamic seals. |
| O-ring inside diameter | mm | Inside diameter of the O-ring from the size standard (e.g. AS 568 or ISO 3601). |
| O-ring cross-section | mm | Cross-section diameter of the O-ring. |
| Groove diameter (bottom for piston, outer for rod) | mm | Piston groove bottom diameter, or rod/bore groove outer diameter. |
| Gland depth (groove bottom to mating surface) | mm | Radial distance from the groove bottom to the mating surface, at nominal clearance. |
| Groove width | mm | Axial width of the groove. |
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: Groove location
- What it is
- Where the groove is: in a piston or male part, so the ring is stretched onto the groove bottom, or in a bore for a rod, so the ring is compressed around its circumference.
- Units and format
- Choose one of 2 options from the list: Piston or male groove (ring stretched onto groove bottom); Rod or female groove (ring fits in a bore groove).
- Example
- The form opens with “Piston or male groove (ring stretched onto groove bottom)” selected as a worked example. Choose the option that matches your case.
- Get it right
- The groove diameter input changes meaning with this choice.
What this means: Duty
- What it is
- Whether the seal is static or moves (reciprocating). It changes only the squeeze range the result is checked against.
- Units and format
- Choose one of 2 options from the list: Static; Dynamic (reciprocating).
- Example
- The form opens with “Static” selected as a worked example. Choose the option that matches your case.
- Get it right
- Choose dynamic for any seal that slides in service.
What this means: O-ring inside diameter
- What it is
- The inside diameter of the O-ring as made, from the size standard or the supplier’s size list.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 10000 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.
- Effect on the result
- For a piston groove, a smaller ring diameter means more stretch and a thinner cross-section.
- Get it right
- Use the ring inside diameter, not the groove or shaft diameter.
What this means: O-ring cross-section
- What it is
- The cross-section diameter of the O-ring cord, from the size standard.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100 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 thicker cross-section raises squeeze and gland fill.
- Get it right
- Measure the cord thickness, not the radial width of the fitted ring in its groove.
What this means: Groove diameter (bottom for piston, outer for r…
- What it is
- The groove diameter: the groove bottom diameter for a piston groove, or the groove outer diameter for a rod (bore) groove.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 10000 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
- Measure the diameter that matches the groove location selected above.
What this means: Gland depth (groove bottom to mating surface)
- What it is
- The radial distance from the groove bottom to the mating surface at nominal clearance; the space the ring cross-section is squeezed into.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100 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 shallower gland raises squeeze and gland fill.
- Get it right
- Include the radial clearance gap to the mating part, not just the machined groove depth.
What this means: Groove width
- What it is
- The axial width of the groove, which with the depth sets the space available for the ring.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100 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 lowers gland fill; squeeze does not change.
- Get it right
- Allow room for fluid swell; a narrow groove raises fill.
Method and formulas
- Piston: stretch = (groove diameter − ring ID) ÷ ring ID. Rod: compression = (ring OD − groove diameter) ÷ ring OD.
- Stretched cross-section ≈ CS ÷ √(1 + stretch) (constant volume).
- Squeeze = (CS′ − depth) ÷ CS′; fill = (π CS′² ÷ 4) ÷ (depth × width).
- Example: a 47.22 × 2.62 ring in the default piston groove has 1.6518% stretch, 19.188% squeeze and 70.154% fill.
Limitations
- Nominal dimensions; repeat at tolerance extremes and with swell in the working fluid.
- Typical ranges used for the checks vary by seal maker and application; confirm with the seal supplier.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check a groove design before release
- Choose an O-ring size for an existing groove
- Investigate a leaking or extruding seal
Who it is for
- Design engineers
- Maintenance engineers
What you get
- Stretch or circumferential compression
- Cross-section after stretch
- Squeeze
- Gland fill
Interpreting the result
- Typical guidance: static squeeze about 15–30%, dynamic about 10–20%, fill below about 85%, stretch up to about 5%.
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
Learn the Concepts Behind This Tool
These BIZOMAT Library readings explain the method this tool uses, with worked examples.
Method explained here · Library collection
O-rings and static seals: gland design, materials, gaskets and why seals fail
In Machine Elements and Mechanical Design
What it covers: How O-rings seal, how to size the groove for squeeze and fill, choosing elastomers for fluids and temperatures, back-up rings, gaskets and sealants, and how to read seal failures.
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