（人工）橡膠密封圈。一般完好使用壽命2-3年吧。之後渣化破損，但還能拖用幾年。
19780年代以前多是用美國（杜邦）的製造的橡膠密封圈。受命比較長。90年代開始黑心渣化用便宜的全球（中國）橡膠密封圈。使用壽命大大縮短。黑心渣會流入飲用水，有可能被飲用，還可能堵塞水龍頭口的過濾網水流膩膩歪歪的（可以打開清理）。
水龍頭開關的金屬配件部分的壽命很久，可達幾十年，所謂Life time。但金屬和金屬無法密封水漏，因為開關擰轉部件配合必須有一定的容納輕鬆活動的間隙。否則太緊壓，無法開關，和或拆裝。機械製造上有個正負DELTA
例如 配合直徑15毫米+-0.05 之類的。如果不加橡膠密封圈的話，這會滲漏水的。
橡膠密封圈會逐漸分解黑渣化。而且開關擰動也會壓力磨損之間的密封圈。這是最弱壽命命部件。幾年後滲漏水很糟心。成本也就是幾分錢。但是你很難買到尺寸材料正好配合的密封圈。所以DIY自己修理時一般是換新一套水閥芯（cartridge），2-30刀。或花錢雇人換新一整套水龍頭，幾百刀；或連台櫃一起換新一整套，順便按裝一套石板麵，幾千刀；或換新整個浴室或廚房，可達幾萬刀。無論你咋換新一套，花多少萬，幾分錢O-ring 還裝在其內，幾年後滲漏水重新糟心。到目前為止，這是個可解的無解問題。
1984年 美國航天機挑戰號因為O-ring泄露導致爆炸的慘劇
Google AI 材料化工信息：
For household plumbing, the most common O-ring materials are EPDM（人工橡膠）, Silicone, and Nitrile (Buna-N). EPDM is generally the ideal choice for most water systems, particularly hot water and steam, while Nitrile is better for applications involving oils or fuels.
Here is a comparison of common household plumbing O-ring materials:
| Material | Temperature Range (approx.) | Primary Resistance To | Weak Against | Key Household Plumbing Use |
|---|---|---|---|---|
| EPDM | -60°F to 300°F (-50°C to 150°C) | Hot/cold water, steam, ozone, UV, weathering, many acids/bases | Petroleum-based oils, fuels, grease, mineral oils | Most common for general plumbing (faucets, shower valves, pipe fittings) |
| Silicone | -75°F to 450°F (-60°C to 230°C) | Extreme high/low temperatures, dry heat, ozone, sunlight, odorless, non-toxic | Abrasion, tear resistance, fuels, mineral oils, concentrated acids | Specialized use in high-temperature applications (e.g., UV disinfection systems) or where flexibility in cold is needed |
| Nitrile (Buna-N) | -40°F to 250°F (-40°C to 120°C) | Oils, fuels, greases, hydraulic fluids, water, good abrasion resistance | Ozone, UV light, steam, brake fluids, strong acids | Applications where contact with oils/greases is expected (e.g., certain valve parts, specific water treatment components) |
Key Considerations for Household Use
- Potable Water Safety: For O-rings used in drinking water systems, materials (especially EPDM and Silicone) must be certified to standards such as NSF/ANSI 61 or WRAS BS6920 to ensure they do not leach contaminants into the water.
- Temperature: EPDM is excellent for the temperature ranges found in standard hot water heaters and supply lines. Silicone can handle higher temperatures (e.g., specific water heating ports) but is less physically durable.
- Chemical Exposure: The main differentiator is resistance to oils/grease vs. water/steam/acids. EPDM will degrade if exposed to petroleum products, while Nitrile will degrade with ozone and certain acids.
- Durability: Nitrile has good abrasion resistance, making it suitable for dynamic seals, while silicone is best suited for static seals due to poor tear strength.
These articles compare the temperature resistance and chemical compatibility of EPDM, Nitrile, and Silicone O-ring materials for plumbing applications.
For most general household plumbing needs (faucets, shower valves, toilet fittings), EPDM is the standard, reliable, and cost-effective choice. Ensure any O-ring you purchase is certified for use with potable water if it will be in contact with drinking water.
EPDM stands for Ethylene Propylene Diene Monomer. It is a type of highly durable synthetic rubber (elastomer) renowned for its exceptional resistance to environmental factors, which makes it a common material for seals, gaskets, and membranes in automotive, construction, and plumbing applications.
Key Properties
- Excellent Weathering Resistance: EPDM has superior resistance to UV radiation, ozone, and general weathering, making it ideal for outdoor applications and long-lasting seals.
- Temperature Tolerance: It functions well across a broad temperature range, typically from approximately -60°F to 300°F (-50°C to 150°C).
- Water and Steam Resistance: It resists hot water and steam very well, which is why it is the go-to material for most household plumbing O-rings and gaskets.
- Chemical Resistance: EPDM offers good resistance to many polar substances, including dilute acids, alkalis, and brake fluids.
- Electrical Insulation: It has good electrical insulating properties, making it useful in electrical applications.
Primary Weakness
The main limitation of EPDM is its poor resistance to petroleum-based products, such as mineral oils, fuels, and greases. Contact with these substances will cause the material to degrade or swell. For applications involving oils, a material like Nitrile (Buna-N) is a better choice.
EPDM is a complex polymer (a large molecule made of repeating subunits), so it does not have a single fixed molecular formula or a simple, specific structural diagram like a small, simple molecule such as water (
H2O
). Its composition is a variable mix of three different monomers. 
Molecular Chemical Formula
The formula for EPDM is represented generally to show the repeating monomer units in a variable ratio:
(C2H4)????⋅(C3H6)????⋅(Diene)????
-
????represents the variable number of ethylene units (C2H4).
-
????represents the variable number of propylene units (C3H6).
-
????represents the small, variable number of diene units.
The ratio of
????
and
????
(ethylene and propylene content) can vary from 45% to 75%, and the diene content is usually low, around 2% to 12% by weight. This variability means EPDM refers to a class of rubber materials, not one specific compound. Structural Formula
EPDM's structure consists of a main saturated carbon backbone (like polyethylene or polypropylene), with a small side chain containing a double bond from the diene monomer. This saturated backbone is key to its excellent resistance to ozone and UV light.
The structural representation is complex and typically shown as a chain of repeating units. The diene monomer used can be one of several types, most commonly:
- Ethylidene norbornene (ENB)
- Dicyclopentadiene (DCPD)
- Vinyl norbornene (VNB)
A simplified representation of the polymer chain backbone (ignoring the specific diene structure) would show a random arrangement of ethylene and propylene units:
—[CH2—CH2]????—[CH2—CH(CH3)]????—[Diene Unit]—
The double bonds on the side chains (from the diene units) are what allow the polymer chains to be cross-linked (vulcanized) with sulfur to form the final elastic rubber material.
