5 Things to Consider When Choosing O-Rings

Spring-energized seals by Monroe Engineering

Choosing the right O-rings is important. Also known as toric joints, they are used in sealing applications. O-rings live up to their namesake by featuring a circular, o-shaped design with a round cross-section. You can secure them around the mating surfaces of fluid- or gas-carrying passages. While all O-rings share a similar design, though, they are available in different types. Here are five things to consider when choosing O-rings.

#1) PSI Rating

The pounds-per-square (PSI) rating of an O-ring refers to how much pressure can withstand without leaking. All O-rings are used in sealing applications. They are used to seal the mating surfaces of pipes, hoses and other passages that carry pressurized substances. When choosing O-rings, you’ll need to make sure that it has a high enough PSI rating to protect against leaks.

#2) Internal Diameter

You should consider the internal diameter when choosing O-rings. Internal diameter is the distance between the two widest points of an O-ring. It essentially reflects the size of an O-ring. The internal diameter of an O-ring must accommodate the passages with which it’s used. If you plan on using an O-ring to seal a pipe, for instance, the internal diameter must be roughly the same size as the pipe. If it’s too big or too small, it won’t fit — at least not without leaking.

#3) Cross Section

In addition to internal diameter, you should check the cross section size when choosing O-rings. What is the cross section exactly? The cross section of an O-ring refers to its thickness. To measure the cross section of a O-ring, you can turn it on the side and measure the O-ring’s thickness. A larger cross section will typically offer greater protection against leaks. With that said, the cross section must still accommodate passages with which it’s used. You’ll need to consider the cross section when choosing O-rings to ensure they fit.

#4) Material

You can find O-rings made of different materials. Some of them are made of rubber. Other O-rings are made of more advanced materials like polyethylene or thermoplastic. Different materials, of course, have different properties. They can all protect fluids and gases from leaks. Nonetheless, their properties vary. When choosing O-rings, consider the material and whether it’s suitable for your sealing application.

#5) Hardness

Don’t forget to consider the hardness when choosing O-rings. Hardness is usually measured with a Shore A Durometer. A hardness rating of 40 indicates the O-ring is relatively soft, whereas a hardness rating of 90 indicates the O-ring is relatively hard.