Firebrick43 said:
as far as o rings go, the best is buna N,,,,,,IF,,,,,, you dont have special needs. certain oils(PAG oil comes to mind require hnbr) or very high heat (viton). Viton is good up to 400 degrees but only down to 0-5 degrees F. Most mobile or even industrial application never see that high heat.
Buna N is good up to 250 but down to -22F. So almost all mobile applications are buna N. Also long term I have noticed that long term(as in decades) viton tends to actually erode a grove more so than Buna N. I know most of you wont ever see that but the machines and engines I work on have 20,000 hour plus overahaul intervals and do have issues with erosion of sealing surfaces.
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HNBR is used for high heat. It is basically a more heat (but not chemical) resistant form of buna N. HNBR is used in air conditioning systems, because the compressor fittings and condensor inlet fitting will get too hot for buna N. It has nothing to do with oil resistance.
Viton does have a higher breakdown temperature, but really, Viton is used where organic solvents may damage buna N. Viton is also a little less abrasion/wear resistant than buna N. As such, it does not make a good substitute in most cases.
Skin said:
...Real Viton is brown and sometimes black, not red. Anything really red is probably silicone...
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Bright red is usually silicone. Most Viton I've seen is a purpley cast of brown. Kind of earthworm is how I'd describe it.
Qualitytools said:
Don't forget Teflon for petroleum applications also as it is considered better than the Viton
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Teflon is not very compressible, so it cannot be substituted for another type of o-ring, since it will not fit in the same dimensions. Plus teflon o-rings don't tend to fail unless they're damaged when you remove them. For these reasons, it makes absolutely no sense to stock a selection of teflon o-rings.
If you want to throw all options out there, there is also polyurethane (these are often clear). I've used them for CO2 seals in air guns, but I haven't seen them elsewhere.
HNBR is used for high heat. It is basically a more heat (but not chemical) resistant form of buna N. HNBR is used in air conditioning systems, because the compressor fittings and condensor inlet fitting will get too hot for buna N. It has nothing to do with oil resistance.Viton does have a higher breakdown temperature, but really, Viton is used where organic solvents may damage buna N. Viton is also a little less abrasion/wear resistant than buna N. As such, it does not make a good substitute in most cases.Bright red is usually silicone. Most Viton I've seen is a purpley cast of brown. Kind of earthworm is how I'd describe it.Teflon is not very compressible, so it cannot be substituted for another type of o-ring, since it will not fit in the same dimensions. Plus teflon o-rings don't tend to fail unless they're damaged when you remove them. For these reasons, it makes absolutely no sense to stock a selection of teflon o-rings.If you want to throw all options out there, there is also polyurethane (these are often clear). I've used them for CO2 seals in air guns, but I haven't seen them elsewhere.
When looking for an O-ring, there are many different materials out there. Viton® and nitrile are two of the most common materials used to create O-rings, and for a good reason. Both have excellent properties, a good compression set, and varied chemical resistances. So which material is suitable for your application?
Nitrile O-rings
Nitrile O-rings, commonly called NBR or Buna-N, are the most frequently used O-ring in the market. These O-rings are also usually the cheapest option out there. However, there are many chemical and environmental limitations to nitrile O-rings.
Nitrile is a synthetic copolymer of acrylonitrile and butadiene, but the percentage of acrylonitrile can change the properties. With a change in the acrylonitrile percentage, the temperature range can be increased but will cause a lower resistance to oil and fuel, and vice versa. Whether increased or decreased, this change in acrylonitrile percentage will increase the cost of the nitrile O-ring.
Additionally, nitrile O-rings can be hydrogenated, also known as HNBR, to increase the temperature range and resist oils, fuels, ozone, and some harsh chemicals. However, this will also increase the cost of the material. For this comparison, let&#;s assume a standard acrylonitrile content is used, and the material is not hydrogenated.
Viton® O-rings
Simply put, Viton® is the name-brand for FKM or FPM material. However, the material is equivalent, whether called Viton®, FKM, or FPM. Viton® O-rings are another extremely common O-ring used due to their high-temperature range and durability.
There are many types of Viton® material used to make O-rings: Viton® A, Viton® B, and Viton® F, as well as many others. The main difference between Viton® A, Viton® B, and Viton® F is the fluorine content, with Viton® A having 66%, Viton® B having 68%, and Viton® F having 70%. Viton® A is the most commonly used version, but Viton® B and Viton® F are also used frequently when the application requires. For this comparison, let&#;s assume Viton® A is used.
Viton® vs Nitrile &#; What is the Difference?
When comparing nitrile and Viton®, the next step is to decide which one is right for your application. But, we still need to better understand the differences between nitrile and Viton® O-rings. So, what is the difference between Viton® vs. nitrile O-rings?
Temperature
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Nitrile O-rings have a temperature range of -35°C (-30°F) to 120°C (250°F).
Viton® O-rings have a temperature range of -20°C (-5°F) to 210°C (-410°F).
Benefits
Viton® O-rings are resistant to more chemicals than nitrile, extreme conditions, and mold. Both Viton® and nitrile O-rings have good abrasion and tear resistance, but nitrile will have higher resistance.
Limitations
Nitrile O-rings perform poorly in harsh chemicals or outdoor applications. Additionally, the resistance to different liquids is reduced when a particular formulation is required for higher or lower temperature ranges. Furthermore, Viton® O-rings should not be used in brake fluid, ketones, hot water, or with low temperatures.
Common Applications & Uses
Viton® and nitrile O-rings are used in various applications. Nitrile O-rings are commonly found in hydraulics, pneumatics, and fuel applications. This is especially true in automotive equipment, off-road equipment, some military applications, marine devices, and aircraft fuel systems. Viton® O-rings can usually be found in automobiles, aircraft, and other mechanical devices, especially those requiring harsher chemicals.
Cost
Nitrile is generally significantly cheaper than Viton®. However, special formulations of nitrile will increase the price.
Which Material Is Right for Your Application?
The suitable material depends heavily on the application. While there are positives and negatives for both nitrile and Viton®, either material may be ideal for your needs. For example, suppose the standard operating temperature is between 0°C (32°F) and 100°C (212°F). In this case, the application is internal, a standard hydraulic oil is used for lubrication, and no harsh chemicals are present; nitrile would be the better option based on the cost.
But, if the temperature were to increase, the applications were to be outside in the elements or in UV, or a harsher chemical would be used, Viton® would be the better option. But, again, a full review of all aspects of your application will help you decide which O-ring is most suitable.
If you need help navigating this process to find the right seal for your project, talk to a seal expert at Wyatt Seal. We&#;ve spent 50 years building relationships with seal manufacturers worldwide to offer you access to thousands of seals, gaskets, O-rings, and other specialty items for any application.
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