Key Takeaways

• O-rings compress between mating surfaces to prevent fluid escape and contamination across industrial, automotive, and hydraulic applications.

• Material selection determines performance: Buna-N suits general hydraulic use, while Viton, Ethylene Propylene Diene Monomer (EPDM), Kalrez, and silicone serve higher-demand environments.

• O-Ring Boss (ORB), flange, O-Ring Face Seal (ORFS), and flared fitting seal types each address specific connection and pressure requirements.

• Specialty materials such as Kalrez (perfluoroelastomer, FFKM) and Viton provide extended service life under extreme temperatures and aggressive chemical exposure.

• Matching seal type and material to the fitting standard, fluid type, and operating conditions is the key to long-term sealing reliability.

O-rings are circular elastomeric rings designed to seal gaps between two or more mating parts. When compressed between surfaces, they form a barrier that prevents fluid escape and contaminant ingress, making them a reliable sealing solution across manufacturing, automotive, aerospace, pharmaceutical, and hydraulic applications. 

What Are O-Rings and How Do They Work?

O-rings are circular, loop-shaped elastomeric rings primarily used to seal gaps between two or more parts. When compressed between mating surfaces, they form a reliable barrier that prevents the escape of fluids and the entrance of contaminants. This makes them useful across manufacturing, automotive, aerospace, pharmaceutical, and hydraulic applications. 

What Role Do Flare-O O-Rings Play in Hydraulic Fittings? 

Flare-O O-rings, typically composed of Buna-N or Viton, are designed for use in hydraulic fittings. These O-rings provide an effective seal that eliminates hydraulic leaks when correctly installed. They are particularly well-suited for Society of Automotive Engineers (SAE) 37-degree flared tube fittings, serving as leak-proof replacements that maintain the integrity of hydraulic systems. Shop Flare-O O-rings. 

How Do Bonded Seal O-Rings Bolster Hydraulic Equipment? 

Bonded Seal O-rings, also referred to as Dowty Seals or Dowty Washers, are commonly used in hydraulic equipment as bolt seals. These seals consist of a metal outer ring and a rubber elastomer inner ring, forming a gasket that provides reliable sealing action. Their versatility extends beyond hydraulic systems, making them useful wherever rubber-to-metal or plastic bonding is required. 

What Are O-Ring Boss (ORB) Seals and Where Are They Used? 

O-Ring Boss (ORB) seals connect two fluid-carrying components such as pipes, hoses, or tubing. In an ORB system, a male-threaded part is inserted into a female-threaded part to create a mechanical seal. An additional nut is tightened over an O-ring seated in a chamfered area, creating a fluid-tight connection. ORB seals are effective in hydraulic systems, compressed air systems, and vacuum pumps. Shop O-ring boss seals. 

What Are Flange Seals and How Do They Provide Static Sealing? 

Flange seals provide front-face static sealing in flange connections and are suitable for both internal and external pressure applications. They are commonly used in tubing applications with larger outer diameters or those subjected to high pressures. An O-ring seats within a groove on the flange and mates with a flat surface on the port, while mounting bolts secure the flange onto the clamp halves for a leak-free connection. Shop flange seals. 

Why Is Buna-N a Common O-Ring Choice for Quick Couplings? 

Buna-N, also known as Nitrile, is a widely used O-ring material in quick couplings. It resists solvents, oils, and water, and operates across temperatures from -40 degrees F to 250 degrees F (-40 degrees C to 121 degrees C). Buna-N is used in engines, gearboxes, aircraft components, and household items. Its flexibility supports both rotary and linear movement, making it suitable for face-to-face gasket-style seals and shaft seal applications. 

When Should You Use Peroxide Cured EPDM O-Rings? 

Peroxide Cured Ethylene Propylene Diene Monomer (EPDM) O-rings offer broad chemical resistance, making them the preferred choice for medical-grade polypropylene couplings, automotive manufacturing, and wastewater systems. EPDM's chemical durability also makes it suitable for household appliance applications. This material is the right choice when chemical exposure would degrade standard elastomers. 

Why Are Viton O-Rings Preferred for Extreme Temperatures and Chemicals? 

Viton O-rings offer exceptional resistance to extreme temperatures and a wide range of chemicals, including ozone, oxygen, mineral oil, synthetic hydraulic fluids, fuels, aromatics, and solvents. Their low gas permeability and compression set resistance make them well-suited for fuel line sealing. Additional fluorocarbon compounds in the Viton family provide enhanced resistance to acids, fuels, water, and steam. Shop Viton O-rings. 

What Makes Kalrez® O-Rings Resistant to Harsh Conditions? 

Kalrez® O-rings are crafted from perfluoroelastomer (FFKM), a material that combines high chemical resistance with the ability to withstand extreme temperatures and pressures. Used across demanding industries, Kalrez® O-rings provide an extended service life and maintain superior chemical resistance under conditions that would degrade standard fluorocarbon elastomers. 

When Should You Choose Silicone O-Rings? 

Silicone O-rings perform best in dry heat environments. With a safe operating temperature range from -70 degrees F to 400 degrees F (-57 degrees C to 204 degrees C), they are used in medical devices, food storage products, electronics, automotive manufacturing, and home repair hardware. 

Which O-Ring Seals Are Used for Flared Fittings? 

Two primary O-ring seal types are used in flared fittings that incorporate O-Ring Face Seal (ORFS) technology: 

ORFS Fittings 

ORFS fittings incorporate a replaceable elastomeric O-ring seated in a groove on the fitting face. A Buna-N, 90 Durometer O-ring compresses against a flat face sleeve brazed onto the end of the tube, creating a metal-to-metal seal. This design minimizes tube twisting and provides structural support during assembly, making it effective in high-pressure hydraulic systems. 

Flare AN Seals 

Flare AN seals, also known as Flare-O O-rings, are designed for 37-degree flare fittings that comply with SAE J514 and ISO 8434-2 standards. Made primarily from Buna-N or Viton, these seals are used at tube end connections where a nut affixed to the flared tube is threaded into a flare fitting. Flare-O seals are most common in aerospace, marine, and older applications that have not transitioned to flareless tube fittings. 

What Are Conical Seals and When Are They Used? 

Conical seals, available in aluminum, copper, nickel, and stainless steel, provide reliable sealing on the end of 37-degree flared fittings of matching dash numbers. These seals address minor nicks or surface defects in the fitting that could compromise sealing performance. Soft annealed 37-degree conical seals function as crush washers on a male Army-Navy (AN) flare, protecting tubing and AN fittings from damage during assembly. 

O-rings are available in a range of types and materials, each suited to specific sealing demands. From general-purpose Buna-N rings used in quick couplings to Kalrez® perfluoroelastomer rings used in high-temperature chemical environments, matching seal type and material to the application is the foundation of long-term reliability. 

Need Help Selecting the Right O-Ring Type?

Royal Brass and Hose provides several resources to support O-ring selection. Learn more in Selecting the Right Type of O-Ring for Your Application, and review performance standards in O-Ring Industry Standards and Certifications. Contact Royal Brass and Hose or call 800-669-9650 to speak with a customer service team member at any of our 11 locations.

Royal Brass and Hose serves customers at 11 locations across the United States: Knoxville, TN; Marietta, GA; Orlando, FL; Charlotte, NC; Little Rock, AR; Fort Worth, TX; Benton, IL; Madisonville, KY; Princeton, WV; Birmingham, AL; and Calvert City, KY. Contact the nearest location to learn more about the O-ring types and materials available.