Fittings 101: ORB

Connection Types: ORB (O-Ring Boss)

What are ORB Fittings?

ORB, or (SAE Straight Thread O-ring Boss) fittings, incorporate a port connection as recommended by the National Fire Protection Association (N.F.P.A.) for leak prevention in medium and high pressure hydraulic systems. ORB connections are commonly manufactured in carbon, nickel plated carbon & stainless steel and typically use Buna-N or Viton, 90 Durometer O-rings. The male connection is a straight UNF thread with an O-ring. The female port has a straight thread and a machined surface to provide a smooth, flat, accurately located surface (minimum spotface), along with a chamfer where the O-ring seats. The seal is created when the O-ring is compressed into the chamfer when mating the male and female connection providing a leak-tight seal. 

Disadvantages of ORB Fittings

  • The relevant temperature rating is limited by the o-ring seal material making these fittings ineffective in high temperature applications
  • The O-ring can be improperly installed resulting in a cut or pinch
  • The fitting could be improperly torqued
  • The threaded portion of the fitting may be longer than SAE specification resulting in the fitting bottoming out in a port before the o-ring can be fully compressed

Advantages of ORB Fittings

  • They’re readily available and offer a large variety of sizes, shapes, combinations and materials
  • Provide optimal sealing performance in medium to high pressure systems
  • The nature of ORB fittings resists complications associated with over-assembly
  • The straight thread connection design coupled with the replaceability of the o-ring makes these fittings reusable and easily maintainable
  • Are either adjustable or non-adjustable 

Adjustable o-ring fittings are typically elbows or tees that are installed in a fixed direction. Non-adjustable o-ring fittings are usually plugs and straight connectors that are fitted into a port without the need for alignment. Options like these make ORB fitting orientation easier than some other fittings because the o-ring is the sealing factor and not the threads. 

ORB fittings can be confused with other connection systems, such as NPT or even JICFor example, this straight thread connection uses the same threads as the JIC 37° fitting. However, the 37° flare has been removed and an o-ring has been added. So, while threads of different connectors sometimes fit, ORB connections should never be used with any other type of connectors as leaks are likely. For these reasons care needs to be taken to properly identify the right connection to create a safe and leak resistant seal.  

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