How do I select the right O-ring size?

Start by identifying the seal application (piston, rod, or face seal), the housing bore or shaft diameter, and the required cross-section. For piston seals, the O-ring OD should match the bore — so ID = bore − 2×CS. For rod seals, the O-ring ID should match the rod diameter. Then select the nearest standard ID from ISO 3601 tables. Target 15–25% squeeze for reliable sealing.

What is squeeze percentage and why does it matter?

Squeeze is the percentage by which the O-ring cross-section is compressed in the groove. Squeeze % = (CS − compressed height)/CS × 100. For dynamic seals (piston/rod), target 10–20%. For static seals (face/flange), 15–30%. Too little squeeze causes leakage; too much causes excessive friction, heat, and premature wear.

What is the effect of stretch on O-ring performance?

Stretch occurs when the O-ring is installed on a diameter larger than its free-state ID. Up to 5% stretch is acceptable for most applications. Stretch reduces the effective cross-section and increases stress in the elastomer. Excessive stretch (>5%) can cause premature failure, especially with hard compounds like FKM/Viton.

What materials are available for O-rings?

Common O-ring materials include NBR (Nitrile, −40 to +120°C, oil-resistant), FKM/Viton (−20 to +200°C, chemical-resistant), EPDM (−50 to +150°C, water/steam), Silicone (−60 to +200°C, food-grade), and FFKM/Kalrez (−25 to +325°C, universal chemical resistance). Material selection depends on temperature, media, and pressure.

When are backup rings needed?

Backup rings (anti-extrusion rings) are needed when the pressure exceeds the O-ring's extrusion resistance — typically above 3.5 MPa (500 psi) for static seals or 7 MPa (1000 psi) for dynamic seals, depending on hardness and gap. Use one backup ring on the low-pressure side, or two for bi-directional pressure. Material is typically PTFE or polyamide.

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O 型環尺寸選擇

依據 ISO 3601 為活塞、桿或端面密封應用找到合適的標準 O 型環尺寸。立即獲取溝槽尺寸、壓縮率與伸長率。

ISO 3601-1 AS568 CS 1.78 – 6.99 mm

應用

截面積 CS (mm)

孔徑 / 軸徑 (mm)

目標壓縮率 (%)

快速預設

結果

建議 O 型環

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溝槽深度

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溝槽寬度

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實際壓縮率

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伸長 / 壓縮

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O 型環內徑（標準）

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O 型環外徑（計算值）

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內徑公差（ISO 3601）

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ISO 3601 標準截面積

CS (mm)	AS568 系列	CS 公差	典型內徑範圍	溝槽深度（20% sq.）	溝槽寬度
1.78	-0XX	±0.08	1–25 mm	1.42	2.50
2.62	-1XX	±0.09	9–76 mm	2.10	3.60
3.53	-2XX	±0.10	15–133 mm	2.82	4.80
5.33	-3XX	±0.13	19–267 mm	4.26	7.15
6.99	-4XX	±0.15	50–292 mm	5.59	9.40

O 型環壓縮率

壓縮率是指 O 型環安裝於溝槽內時，其截徑向的壓縮量。它會產生初始的密封接觸應力。

動態密封 （活塞/桿）：建議壓縮率 10–20%
靜態密封 （端面/法蘭）：建議壓縮率 15–30%

溝槽尺寸

溝槽寬度必須允許 O 型環在受壓時向側向膨脹，並容納熱膨脹與溶脹。

伸長與壓縮

對於活塞密封，O 型環需套在活塞上伸長。對於桿密封，則需壓縮裝入孔溝槽中。

最大伸長率： 5%（標準彈性體），3%（PTFE、硬質化合物）
最大壓縮率： 內徑的 3%

範例 — 活塞密封，孔徑 Ø50 mm，截徑 3.53 mm

目標： O 型環外徑 ≈ 孔徑 = 50 mm

所需內徑 = 50 − 2 × 3.53 = 42.94 mm

最接近的標準內徑： 42.86 mm → 外徑 = 42.86 + 2 × 3.53 = 49.92 mm

溝槽深度（20% 壓縮率）= 3.53 × 0.80 = 2.82 mm

溝槽寬度 = 3.53 × 1.35 = 4.77 mm

溝槽底部直徑* = 50 − 2 × 2.82 = 44.36 mm

伸長率 = (44.36 − 42.86) / 42.86 × 100 ≈ 3.5% ✓（在 5% 限制內）

*假設活塞外徑 ≈ 孔徑；需從活塞外徑中減去活塞與孔的間隙，以獲得精確的溝槽底部直徑

⚠️ 注意： 務必驗證溝槽填充率（O 型環體積與溝槽體積之比）。O 型環應填充溝槽的 70–85%。填充不足會導致不穩定；填充過滿則會妨礙熱膨脹並導致擠出。

ℹ️ 提示： 當壓力高於 3.5 MPa（靜態）或 7 MPa（動態）時，請在低壓側添加備用環，以防止 O 型環擠入間隙。