The O-Ring: More Than Meets the Eye

Most of us benefit from o-rings in our everyday lives without even realizing it. The o-ring is a simple product but is fundamental in the functioning of so many processes and devices. Because of its importance to many devices and processes, when an o-ring fails, production or use of a product has to be halted. Having some basic knowledge about o-rings, and where to buy quality replacements, can help you avoid o-ring failure or at least allow you to get back online quickly when one does reach the end of its life.

History of the O-Ring

Like all things, the o-ring had to start somewhere. While the o-ring is a simple product, it is one with a rather interesting history. The o-ring was invented by Niels Christensen in 1936 just before the war. The o-ring quickly became a fundamental product, with many violating the patent rights of Christensen’s design. Interestingly, to fulfill needs and get around patent violations, the United States Government bought the patient from Christensen for just $72,000. While that was a great sum of money in those days, the idea that something so fundamental even today was purchased for relatively little is remarkable.

Because the o-ring is relatively simple, the general design has stayed the same. While it was a relatively new invention when purchased by the government, today it is used in a wide variety of applications and available in many different materials.

O-Ring Offerings Today

While the overall design of the o-ring has stayed much the same since Christensen invented it, today it is offered in a variety of different materials. The most common materials include but may not be limited to:

• Nitrile (Buna-N)

• Fluoroelastomer

• Chloroprene

• Silicone

• Highly saturated nitrile

• Ethylene Propylene (EPM, EPDM, EPR)

• PTFE

• Aflas

Why so many different material offerings? With o-rings being used in an increasing number of applications, the same material wasn’t effective for all operating temperatures or exposure to different liquids or weather. Manufacturing o-rings out of a variety of different materials allows for every application to use a material that best suits operating temperature and other operating elements. Each of these materials features its own temperature range, operating pressure, surface finish, and stretch. With so many options, users find that their o-rings can function more reliably and without premature failure.

Material Selection

If you’re buying o-rings for the first time you may be shocked by the material offerings. Knowing what materials offer in terms of shore hardness and temperature tolerance can help you get started:

Aflas offers high temperature, chemical, and electrical resistance properties. It offers a shore hardness of 70 to 90 durometer and a temperature range of +25° - +450°F. Aflas is compatible with a wide variety of substances such as oils, lubricants, transmission fluid, hydraulic fluids, power steering fluid, sour oil and gas, steam, acids, bases, alcohols, ozone, and more.

Chloroprene offers a temperature range of -65°- +250°F with a durometer of 25-90. It offers moderate resistance to petroleum and offers good weather and ozone resistance. This material an excellent option for sealing refrigeration fluids such as Freon.

Ethylene Propylene(EPM, EPDM) (EPR)offers an excellent resistance to Skydrol fluids used in commercial aircraft hydraulic systems. This elastomer offers a shore hardness ranging from 70-90 durometer and is recommended for use with hot water, steam, and phosphate ester-type hydraulic fluids as well as resistance to some acids, bases, and ozone with a temperature range of 65° - +300°F.

Fluoroelastomer is a material that offers good resistance to petroleum products and a temperature range of -15° to +400°F. This material offers a shore hardness of 60 to 90 durometer and is ideal for vacuum service and low gas permeability.

Highly saturated nitrile offers better resistance to high temperature and improved chemical resistance over traditional nitrile compounds. This material has a temperature range of -40°- +325°Fand a shore hardness of 70 to 90 durometer.

Nitrile (Buna-N) is the most used material for o-rings with hardness offerings ranging from 40-90 durometer. This material offers excellent resistance to petroleum products as well as excellent compression set, tear, and abrasion resistance. The temperature range for this material is -40° to +250°F.

PTFE is a white thermoplastic fluoroethylene resin that offers a temperature range of -65°- +500°F. This material offers heat resistance, dielectric strength, weatherability, low friction, toughness, no water absorption, and flexibility.

Silicone is an elastomer that is ideal for weather and ozone with a shore hardness of 30 to 90 durometer. This material offers limited resistance to oil and is not recommended for dynamic sealing applications because of poor tensile and tear strength and low abrasion resistance. The temperature range for this material is -80° - +450°F.

As you can see, there are a variety of different materials that you can choose from to ensure that you purchase an o-ring that is perfect for your application.

O-Ring Sizing

Not sure what size o-ring to purchase? It can be difficult to determine what size you need if you are not all that familiar with o-rings and how to measure them. Luckily, once you learn the different measurements and how to find them, it is not all that difficult to ascertain what size you need.

Figure 1: Measuring O-Rings

If you are in doubt, you can always give our customer service department here at APG a call and we can help you determine what size o-ring you need for your specific application. Unsure of the shore hardness of the o-ring you need? We can help with that, too! All things o-rings, even helping our customers understand sizing and standards is our expertise!

Installing an O-Ring

Have you recently purchased an o-ring and now it’s time to put it to work? Installing an o-ring may sound intimidating, but when you have the right lubricants, the right size oring, and the right tools on hand you’ll find that it is generally very easy to do.

It is important before you begin the installation process that you double-check the size one more time. Then, you’ll want to lubricate the ring well. Before you choose any lubrication, be sure that it is compatible with the specific material you have chosen. The lubrication will help you simply slip the o-ring into place.

Vulcanized O-Rings

Can’t find the size o-rings you need for an odd-sized application or is the size you need often sold out? This is when vulcanized o-rings can come in handy. While this type of o-ring is not the best option for every application, it is a great option in many industries including but not limited to manufacturing, food and beverage, construction, agriculture, semiconductor, and energy.

APG has vast experience creating vulcanized o-rings for a variety of industries and applications big and small. Not sure your application is compatible with vulcanization? We can help!

APG is Ready to Assist with All of Your O-Ring Needs

At APG we have been providing our customers with the o-rings they need since 1943. In that time, we have learned a lot about manufacturing the best quality o-rings on the market, as well as how to assist our customers in purchasing the products that are best suited for their specific applications. We invite you to shop our selection any time and if you need assistance we are always here to help!