All You Need To Know About O-Ring Fittings

All You Need To Know About O-Ring Fittings

Hydraulic fuel efficiency, power losses and higher costs of operations are some of the most common problems of using pneumatics and hydraulic-power based machinery. O-ring fittings are a commonly used component to plug these leaks and prevent leaks in the future. It’s a simple tool, but any amount of attention given to O-rings will fall short of the ideal emphasis we should put on them.

For perspective, the space shuttle Challenger’s engine exploded because of faulty O-ring fittings that couldn’t bear the heat from propellant gases—the disaster cost $3.2 billion and the lives of 7 astronauts. At best, a small hydraulic leak will cost you $1000 in repairs and clean-up—assuming you’re not using the best O-Ring fittings in your systems. Additionally, hydraulic oil leaks cost $250 million in oil replacement alone and efficiency losses as high as 50%.

Based on these statistics, there’s nothing more important than knowing how O-Ring fittings work and the standard shelf lives for each O-Ring fitting made with different materials.

Types and Functions of O-Ring Fittings

O-ring fittings are used in fluid power connections to minimize the risk of leaks in valves, pipes, and cylinders. Used in both pneumatic and hydraulic machinery as well as static and dynamic systems, O-ring fittings are fundamental components of your tools and machinery. They are made from various materials including polymers and metals—depending on where an O-ring is needed.


When we describe O-ring fittings, it’s simpler to speak of them in terms of the types of fittings and the types of O-rings used in specific fittings. The types of O-ring fittings include:

  • O-ring Boss Connections—You fit a male-threaded part into a female threaded part to create a mechanical seal. An additional nut is tightened over the seal into a chamfered area to create a fluid-tight seal. Used commonly in vacuums, hydraulic and compressed air systems.
  • Flange Connections—Used for tubing having outside diameters of over 7/8 inches.

The types of O-rings include:

  • Flare O-rings— When used on hydraulics, these are usually leakproof and serve as replacements for SAE 37° flared tube fittings.
  • Bonded Seal O-rings—Used as bolt seals on hydraulic equipment and in places where a combination of rubber-metal sealing is needed.
  • Conical Seals—Designed to overcome defects in existing systems that don’t let you plug leaks.

 The Standards for Shelf Life


Fortunately, the SAE has specified the ideal conditions that maximize the shelf life of O-rings.  The SAE International Standard ARP2316D specified the following conditions:

  • Humidity Considerations—O-rings and O-ring fittings should be kept in moisture-proof bags with humidity rates below 75%. Polyurethane fittings should be kept in surroundings with humidity below 65%.
  • Light—All light exposure must be avoided.
  • Ozone—You shouldn’t expose your O-rings and fittings to ozone, equipment using ozone and combustible gases/vapors.
  • Radiation—O-rings shouldn’t be exposed to any ionizing radiation.
  • Temperatures—All O-rings and O-ring fittings should be kept in temperatures beneath 100°F.

Assuming you follow these rules, the shelf lives of O-rings should follow these rules:

  • Polyurethane, polyisoprene and natural rubber O-rings and fittings will last 5 years.
  • Butyl, polyacrylate and HNBR rings and fittings will last 15 years.
  • Aflas, ethylene propylene, silicon and fluorocarbon fittings, and rings will last you forever.

Looking For Quality Pneumatic Fittings?

Utah Pneumatic is a one-stop-shop for state-of-the-art pneumatic fittings including push to connect air fittings, quick connect fittings, and nylon air hose fittings sourced from top-tier vendors in the industry. We also provide air filter regulators at affordable prices!

Browse through our catalog or get in touch with us for more information.

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