O-Rings: Viton vs. Buna-N

We’re back with another dose of knowledge from the one and only Precision Pete. Last time we discussed how to prevent pump leaks and proper pump maintenance. Now that all your vacuum pumps are up and running as smoothly as ever, I’d like to take the opportunity to explore some useful information that can be utilized not only for pumps but in a variety of mechanics. Today I want to talk about o-rings, a common tool used in the manufacturing industry. You’ve heard of them, you’ve seen them at work, and most likely, used in everyday life. Despite what the common person may think, o-rings are one of the most simplistic, yet essential mechanical parts ever created for proper machine function and safety. Don’t believe me? What do you think caused the Challenger space shuttle disaster? I’ll wait until you’re back from Google. In this blog we’ll be debating the differences between Viton and Buna-N o-rings, champions of the gasket world and chosen standards used in vacuum pumps.

Let’s start with the basics. An o-ring, by definition, is a gasket in the form of a ring with a circular cross section, typically made of a pliable material used to seal connections in pipes, tubes, and so forth. In our everyday life we see o-rings used on common items like garden hoses, faucets, and showerheads; however, they are also heavily used in engines, pumps, automobiles, aircrafts, and even rockets. Because there is such a variety of materials used to manufacture o-rings, the uses for them can be just as diverse. Most are made from rubber that has been cured to make it stronger, durable, and more flexible. Depending on the material that is used, properties vary as far as strength, durability, and flexibility; on top of other qualities.

Buna-N, commonly known as Nitrile, is made by the reaction of monomers butadiene and acrylonitrile. These nitrile based seals come with a low cost and are the most commonly used o-ring in the seal industry. Buna-N is highly resistant to petroleum oils and greases, and can be compounded to be resistant to temperatures ranging from -65°F to 300°F; they are generally used as seals for machines that operate with petroleum oils, water, and hydraulic fluids. Some other highlighting features of Buna-N o-rings are:

  • Resistance to many standard lubricants, synthetic base lubricants, compression set, abrasion, alcohol, silicone and mineral grease/oil, and many more.
  • Exceptional mechanical properties, allowing both rotary and linear movement.
  • Varietal fluid compatibility
    • HFA (High Water Content)
    • HFB (Fire Resistant Fluids)
    • HFC (Water Glycol Fluids), more popularly used

The use of plasticizers with crystalline acid (pthalates) when compounding Nitrile rubber does however cause some limitations because of the potential of migrating out and causing problems with other plastics. The use of pthalates has also been limited because of newly made regulations. Other limitations include:

  • Ozone
  • Direct sunlight, UV
  • Weathering
  • Aromatic Fuels
  • Glycol based brake fluid
  • Polar solvents
  • HFD (Non-flammable Hydraulic Fluid)
  • Certain Hydrocarbons, aromatic/chlorinated
  • Strong acids
  • 15 year shelf life


Viton, also called Fluoroelastomers (FKM), is a high-performance rubber with superior resistance to a variety of elements such as high temperatures ranging from -15°F to 450°F and an assortment of chemicals. These chemicals include aliphatic compounds, mineral and vegetable oils/grease, organic solvents and chemicals, HFD’s, fuels, aromatic and chlorinated hydrocarbons, and acids. Other Viton features worth noting are its:

  • Low gas permeability and compression set
  • Resistance to ozone and aging
  • Ability to guard against seal failure and prolong maintenance intervals

Fluoroelastomer o-rings have initiated new standards in performance for advanced fuel and engine systems. They have also proved to be more reliable in system performance in extreme temperatures for transmission fluids, fuels, and oils.

Viton limitations include:

  • Hot water, steam
  • Organic compounds
  • Polar solvents
  • Organic solvents with low molecular weight
  • Ammonia gas
  • Glycol based brake fluids

O-ring manufacturing consists of such a variety of materials that one might find it hard to decide which type might work best for a project. In comparison, both Viton and Buna-N are susceptible to ethers, esters, ketones, amines, and glycol based brake fluids. Buna-N are favorable because of their low cost and versatility in the world of seals and can be used in a number of pump varieties, but are not effective against a list of harsher chemicals and age. Viton, in addition to its usable age length, gains appeal from its superior resistance ability when dealing with high temperatures and a broadened range of chemicals; but comes at a higher cost.

When working with potentially harmful chemicals, machines, and substances; your actions must always be precise. That’s why precision comes first when looking for your go to guide for your vacuum pump success, it’s in our name. Thank you again for choosing Precision Plus, the trusted choice for vacuum pump replacement parts . Check back with us every month for new blogs!

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