What is the recommended squeeze percentage for static vs dynamic O-ring glands?

For static radial and axial face seals, nominal squeeze should be 15% to 25% (target ~20%) to guarantee seal integrity across manufacturing tolerances. For dynamic reciprocating seals, squeeze is reduced to 10% to 18% (target ~15%) to prevent excessive friction and wear. For dynamic rotary seals, squeeze is minimized to 2% to 5% with peripheral compression to counter the Gough-Joule elastomer contraction effect.

Why must O-ring gland volume fill remain below 85%?

Elastomers behave as virtually incompressible hydraulic fluids (Poisson ratio ν ≈ 0.499). If thermal expansion or fluid absorption increases O-ring volume beyond the available gland void volume (>85% to 100% fill), the elastomer hydrostatically exerts immense forces against the metal gland walls, causing joint separation, galling, or severe extrusion.

When are anti-extrusion backup rings (BUR) required?

Standard 70 Shore A O-rings begin extruding into diametral clearance gaps above 100 bar (1500 psi). Between 100 and 200 bar (1500–3000 psi), either 90 Shore A elastomer or one PTFE backup ring on the low-pressure side is recommended. Above 200 bar (3000 psi) or for reversing pressure cycles, two backup rings (or contoured hard thermoplastic rings) are required and the groove width must be widened accordingly.

How does installation stretch affect the O-ring cross-section?

When an O-ring is stretched over a piston or shaft during assembly (target 1.0% to 5.0%, maximum 8.0%), constant volume conservation reduces its effective cross-section according to W_reduced = W_nominal × sqrt(100 / (100 + Stretch%)). This reduced cross-section must be used when sizing groove depth to maintain correct squeeze.

What are the design rules for a 65° dovetail O-ring groove?

Dovetail glands retain the O-ring in overhead or vertical lid surfaces during disassembly using a 65° included angle undercut. Squeeze is typically maintained at 18% to 25%, with top throat opening 85% to 90% of free cross-section and total gland fill kept between 65% and 75% to accommodate corner entrapment without pinching.

Sealing & Fluid Power

SAE AS568 / ISO 3601-2

PRO Suite

O-Ring Gland & Groove Sizing PRO Calculator

Size standard SAE AS568 and ISO 3601-1 O-ring glands per ISO 3601-2 / Parker ORD 5700. Analyze squeeze percentage, gland fill volume, installation stretch, 65° dovetail retention geometry, and high-pressure anti-extrusion backup rings.

Input Parameters

Calculation Workflow Mode

Measurement System

Gland Configuration & Service

Pressure on outer diameter, groove turned in moving/static piston core.

O-Ring Standard Specification

AS568 Dash Number Size:

Operating Environment & Material

Applied Pressure (bar):50 bar

Operating Temp (°C):20 °C

Elastomer Compound:

Durometer Hardness:

Fluid Swell / Shrinkage (%):0%

Force Anti-Extrusion Backup Ring

O-Ring Squeeze, Fill & Extrusion Audit

Optimal Squeeze (20.0%)

Optimal Fill (70.9%)

Nominal Squeeze20.0 %Band: 15–25 % (Opt 20%)

Gland Fill70.9 %Opt 70–80% (Max 85%)

Installation Stretch-13.23 %Target 1.0–5.0% (Max 8%)

Radial Gap / Allowed2.860 / 0.185mm · Extrusion: Critical Hazard

Squeeze & TolerancesSAE AS568D / ISO 3601-1

O-Ring Size / Section (W):AS568 -214 (W = 3.530 mm)

Reduced Section (W_red):3.790 mm

Squeeze Range (Min / Max):16.1 % / 23.7 %

Groove Depth (L ± Tol):2.824 ± 0.050 mm

Groove Width (G ± Tol):5.648 ± 0.130 mm

Corner Radius (R) / Finish:R 0.21 mm · 1.6 µm Ra

Extrusion & Thermal CheckNBR (Nitrile / Buna-N)

Diametral Clearance (E):5.720 mm

Hardness (Current / Recom):70 ShA / 70 ShA

Backup Rings Required:1 ring (unidirectional)

Widened Width (G_eff):7.048 mm (+1.40)

Swell / Temp Squeeze:+0.0% swell → 25.5% squeeze

Temperature Margin:80.0% (Within Limits)

Engineering Design Alerts & Constraints:

ID stretch -13.2 % is below the 1.0 % minimum. A loose ring will not seal and can fret against the groove wall.
Radial gap 2.8600 mm exceeds the 0.1853 mm allowable for 70 Shore A at 50 bar. Fit 1 backup ring or raise hardness to 70 Shore A.

Gland & O-Ring Cross-Section Visualizer

radial-piston

Elastomer (NBR (Nitrile / Buna-N))Metallic GlandAnti-Extrusion Backup Ring (1x)

Fill: 70.9% (Groove Area 15.9 mm²)

High-Pressure Extrusion Limits & Backup Rings

Risk: CRITICAL

Operating Point

50 bar

Gap E = 5.720 mm

Hardness Grade

70 ShA

Allowable Gap: 0.185 mm

Backup Rings

1 Ring (Unidirectional)

Groove: 7.05 mm (+1.30 ea)

Design Rules (Parker ORD 5700 & ISO 3601-2):

• Below 100 bar (1500 psi): 70 Shore A handles radial gaps up to 0.13 mm without backup rings.

• 100 to 200 bar (1500–3000 psi): Upgrade compound to 90 Shore A or install 1 PTFE backup ring on low-pressure side.

• Above 200 bar (3000 psi): 2 backup rings or contoured anti-extrusion rings required; groove axial width must be widened accordingly.

Calculation Summary

Input Parameters

O-Ring Specification	AS568 -214
Nominal Size	62.21 ID × 3.53 CSmm
Gland Application	radial-piston
Elastomer Compound	NBR (Nitrile / Buna-N) (70 ShA)
System Pressure	50bar
Operating Temperature	20°C

Calculated Results

Recommended Groove Depth (L)	2.824 ± 0.050mm KEY
Recommended Groove Width (G)	7.048 ± 0.130mm KEY
Nominal Squeeze	20.0% (Range 16.1–23.7%) KEY
Gland Volume Fill	70.9%(Optimal 70–80%)
Installation Stretch	-13.23%(Target 1–5%)
Extrusion Safety & Backup Rings	1 Backup Ring(s) Req KEY

Safety Notes

Gland design verified against SAE AS568D / ISO 3601-2 / Parker ORD 5700. Nominal squeeze is 20.0% with 70.9% gland fill and CRITICAL extrusion hazard at 50 bar.

Mathematical Models & Equations

Diameter Stretch on Installation (§2.1)

Stretch_{ID} = \frac{D_{groove} - ID}{ID} \times 100 \quad [\%], \qquad 1.0 \le S \le 5.0, \; S_{max} = 8.0

Cross-Section Reduction Under Stretch (§2.1)

W_{reduced} = W_{nominal} \sqrt{\frac{100}{100 + S_{ID}}}

Squeeze (§2.2)

S_{nom} = \frac{W_{reduced} - L}{W_{reduced}} \times 100, \quad S_{min} = \frac{W_{min} - L_{max}}{W_{min}} \times 100, \quad S_{max} = \frac{W_{max} - L_{min}}{W_{max}} \times 100

Recommended Groove Depth from the Target Squeeze (§2.2)

L = \sqrt{W_{nom}^2 \left(1 - \frac{S_{opt}}{100}\right)}

Gland Cross-Sectional Area (§2.3)

A_{groove} = (L \times G) - (4 - \pi) R^2, \qquad A_{oring} = \frac{\pi}{4} W_{reduced}^2

Gland Fill Percentage (§2.3)

Fill = \frac{A_{oring}}{A_{groove}} \times 100 \quad [70 \ldots 80 \text{ optimum}, \le 85 \text{ max}]

Thermal Expansion and Fluid Swell (§2.4)

A_{oring}(T) = A_{20} \left[1 + 2 \beta_{elast} \Delta T\right] \left[1 + \frac{S_{swell}}{100}\right], \quad \beta_{elast} \approx 1.5 \ldots 2.0 \times 10^{-4} \,/^\circ C

Diametral Clearance and Radial Gap (§2.5)

E = D_{bore} - D_{shaft}, \qquad g = \frac{E}{2}

Allowable Extrusion Gap (§2.5)

g_{allow} = 0.10 \, \frac{70}{Shore} \, \frac{100}{P} \, \frac{D_{ref}}{D} \, \left(1 - 0.1 \Delta T\right) \ [mm]

Backup Ring Groove Widening (§2.5)

G_{eff} = G_{standard} + n_{backup} \, t_{backup}, \qquad t_{backup} \approx 1.25 \ldots 1.4 \ [mm]

Dovetail Retainer Geometry (§4)

W_{top} = L \left(1 - \frac{S_{opt}}{100}\right) + 0.15\, W_{reduced}, \qquad W_{bot} = W_{top} + 2 L \tan\left(\frac{90^\circ - 65^\circ}{2}\right)

Verification Calculation Log

1O-Ring Selection — SAE AS568D / ISO 3601-1:
- •Size AS568 -214: ID = 62.21 mm, cross-section W = 3.530 mm
- •Tolerance band: W_min = 3.424 mm, W_max = 3.636 mm
2Installation Stretch and Cross-Section Reduction:
- •S_ID = (D_groove − ID) / ID × 100 = -13.23 % → UNDER-STRETCH (target 1.0–5.0 %, absolute max 8.0 %)
- •W_reduced = W_nominal × √(100 / (100 + S_ID)) = 3.7896 mm
- •The cross-section at installation is smaller than the free-state size — sizing squeeze on W_nominal alone overstates the squeeze in the groove.
3Gland Squeeze — Static Radial — Piston Seal:
- •Gland depth L = 2.824 mm (tolerance ±0.050 mm)
- •S_nom = (W_reduced − L) / W_reduced × 100 = 20.00 %
- •S_min = (W_min − L_max) / W_min × 100 = 16.07 %
- •S_max = (W_max − L_min) / W_max × 100 = 23.71 %
- •Target band 15–25 % (optimum 20 %) → OPTIMAL
4Gland Fill:
- •Groove width G = 5.648 mm, corner radius R = 0.212 mm
- •A_groove = (L × G) − (4 − π)R² = 15.91 mm²
- •A_oring = (π/4)·W_reduced² = 11.28 mm²
- •Fill = A_oring / A_groove × 100 = 70.89 % → OPTIMAL (70–80 % optimum, ≤ 85 % max)
5Extrusion Clearance and Backup Rings:
- •Diametral clearance E = D_bore − D_shaft = 5.720 mm → radial gap g = E/2 = 2.8600 mm
- •Allowable gap g_allow for 70 Shore A at 50 bar = 0.1853 mm
- •Extrusion risk: CRITICAL
- •Recommended: 1 backup ring, 70 Shore A, t_backup = 1.30 mm
- •Groove width widened to G_eff = 7.048 mm
6Thermal and Swell Check — NBR (Nitrile / Buna-N):
- •Service 20 °C (reference 20 °C), volumetric swell 0.0 %
- •A(T) = A₂₀ × [1 + 2βΔT] × [1 + S_swell/100] = 11.28 mm²
- •Effective section at service temperature = 3.7896 mm → squeeze 25.48 %
- •Temperature margin to compound limit: 80.0 % (WITHIN LIMITS)

Engineering DisclaimerEngineering calculations are provided for preliminary design and educational/reference purposes only. Users must verify all results according to applicable engineering standards, supplier data, manufacturing requirements, and professional engineering judgment.

Groove Depth (L):	2.824 ± 0.050 mm
Groove Width (G):	7.048 ± 0.130 mm
Corner Radius (R):	R 0.21 mm
Nominal Squeeze:	20.0% (optimal)
Gland Fill:	70.9% (optimal)
Installation Stretch:	-13.23%
Backup Rings:	1 ring(s)

Groove Depth (L):	2.824 ± 0.050 mm
Groove Width (G):	7.048 ± 0.130 mm
Corner Radius (R):	R 0.21 mm
Nominal Squeeze:	20.0% (optimal)
Gland Fill:	70.9% (optimal)
Installation Stretch:	-13.23%
Backup Rings:	1 ring(s)

O-Ring Gland & Groove Sizing PRO Calculator

O-Ring Squeeze, Fill & Extrusion Audit

Gland & O-Ring Cross-Section Visualizer

High-Pressure Extrusion Limits & Backup Rings

Calculation Summary

Mathematical Models & Equations

Verification Calculation Log

O-Ring Gland Sizing & Squeeze Verification Report — Calculation Report

O-Ring Gland Sizing & Squeeze Verification Report

Design Inputs

Calculated Results

O-Ring Squeeze, Fill & Extrusion Audit

Gland & O-Ring Cross-Section Visualizer

High-Pressure Extrusion Limits & Backup Rings

Calculation Summary

Mathematical Models & Equations

Verification Calculation Log

O-Ring Gland Sizing & Squeeze Verification Report — Calculation Report

O-Ring Gland Sizing & Squeeze Verification Report

Design Inputs

Calculated Results