What is a radial lip seal?

A radial lip seal (oil seal) is a sealing element that prevents leakage of lubricant from a bearing housing along a rotating shaft. It consists of a flexible lip pressed against the shaft by a garter spring, a metal case for press-fitting into the housing bore.

How do I select the right seal size?

Seal size is determined by three dimensions: shaft diameter (d), bore/housing diameter (D), and width (b). Standard sizes per ISO 6194 follow preferred number series. The shaft must have appropriate surface finish (Ra 0.2–0.8 μm) and hardness (≥45 HRC).

What is the maximum speed for a standard lip seal?

Standard NBR lip seals work up to a peripheral speed of about 12–15 m/s. FKM (Viton) seals can handle slightly higher speeds. PTFE seals can reach 20+ m/s. The peripheral speed v = π × d × n / 60000 (m/s).

What seal material should I choose?

NBR (Nitrile): -40 to +100°C, mineral oil, general purpose. FKM (Viton): -25 to +200°C, synthetic oils, fuels, chemicals. PTFE: -60 to +200°C, aggressive chemicals, high speed. EPDM: water, steam, brake fluid (not oil-compatible).

Can lip seals handle pressure?

Standard lip seals are designed for near-zero pressure (splash lubrication). For pressures up to 0.05 MPa (0.5 bar), a standard seal may work. Above 0.03–0.05 MPa, use a pressure-rated seal with backup ring or consider a mechanical seal.

Free Engineering Tool

Shaft Seal Selection — ISO 6194

Select radial lip seals per ISO 6194. Enter shaft diameter, speed, and medium to get recommended seal type, dimensions, and material.

ISO 6194Radial Lip Sealsd × D × b

Recommendation

Recommended Seal (d × D × b)

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Material

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Peripheral Speed

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Speed Check

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Seal Type

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Peripheral Speed

Standard NBR lip seals: max ~12 m/s. FKM: ~14 m/s. PTFE: ~20 m/s.

Material Selection Guide

NBR (Nitrile): -40 to +100°C. Mineral oil, grease. General purpose. Most common.

FKM (Viton): -25 to +200°C. Synthetic oil, fuels, high temp. Premium choice.

PTFE: -60 to +200°C. Aggressive chemicals, high speed, dry running.

EPDM: -50 to +150°C. Water, steam, brake fluid. NOT compatible with mineral oil.

Shaft Seal Selection — ISO 6194 | Free Online Tool

Published by Nikolai Shelkovenko on February 15, 2026 February 15, 2026

Recommendation

Peripheral Speed

Material Selection Guide