Ethylene-propylene diene (EPD) is usually compounded with a third monomer to produce what is most commonly referred to as EPDM rubber. EPDM o-rings are frequently used to seal brake systems and in many hot water and steam applications. Additionally, EPDM compounds have good resistances to; mild acids, detergents, alkalis, silicone oils and greases, ketones, and alcohols. EPDM has gained wide acceptance in the o-ring and rubber seal industry due to these excellent chemical resistance properties and its superior ozone resistance. In applications with petroleum oils, mineral oil, die-ester lubricants or fuel exposure EPDM is not recommended. EPDM is sometimes referred to by the following trade names; EP, EPT or EPR.
The NSF 61-Standard is used to establish minimum requirements for the control of potentially harmful contaminants leaching into drinking water as a result of water interacting with the faucet components. Rubber compounds submitted to the NSF go through rigorous testing to determine if these standards are met. For more information on this standard refer to the NSF web site.
The EPDM NSF 61 AS008-E70-8172 o-ring can be reference in one of four ways:
The final consideration for an o-ring after size and material type is the durometer. Durometer is an industry standard measurement for a material’s hardness. Most often for rubber seals, durometer is measured and listed in accordance with the “Shore A” scale. Typical durometers for standard rubber seals are 70, 75 and 90, depending on the material. A higher number indicates a harder material. Durometer is also generally stated and accepted with a “+/- 5” tolerance. For EPDM o-rings, the standard nominal durometer is 70.
O-Rings, rubber seals and custom molded rubber components for:
Low: | High: |
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-60`F / -51`C | 300`F / 149`C |
Properties | Excellent | Good | Fair | Poor |
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Petroleum Oils / Fuels | ![]() |
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Tear Strength | ![]() |
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Steam Up to 399`F | ![]() |
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Gas Impermeability | ![]() |
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Compression | ![]() |
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Abrasion Resistance | ![]() |
AS568-008 (Durometer 70) cross reference sizes