Posted on February 06, 2019

Common Hydraulic Fitting Types & Applications: Part II

Kelly Forrest
Written by

Kelly Forrest

Posted in
Fittings, Tube Fittings

hydraulic fitting types and applicationsThis post is a continuation of our blog "Common Fitting Types & Applications: Part I"

Some additional common hydraulic fitting types include:

SAE J1453 O-RING FACE SEAL FITTINGS: The metal-to-metal seals of flare and flareless fittings are the best choices for many applications, yet they are not as reliable as O-ring seal fittings when it comes to maximum sealing in many lower pressure applications. 

O-rings are very popular among equipment designers because of their leak-tight connections, typically using a 90 durometer, Buna-N (Nitrile) O-ring.

SAE J1453 O-RING FACE SEAL: O-ring face seal J1453 fittings comprise of a body, nut, O-ri

ng and sleeve, and are used in assemblies for nominal tube or hose diameters of 0.25 inches (6.35 mm) to 1.5 inches (38.1 mm). They are most widely used in hydraulic systems and general applications where O-ring seals are acceptable to prevent leakage on industrial equipment and commercial products.

SAE J1453 also covers hose tail (hose barb) fittings and formed tube connections that incorporate O-rings. As with all connection designs, it is important to note that these connections do not exceed the rated working pressure of the lowest-rated component. For instance, if the required system working pressure for a ½ inch hose assembly needs to be 2,000 PSI, then:

• The hose could be ½ inch rated to 3,000 PSI
• The compatible hose tail fitting components may be rated at 2,000 PSI

Therefore the maximum working pressure for the assembly is the least of the two components; i.e. 2,000 PSI. 

SAE J1926-1 (ISO 11296-1) STRAIGHT-THREAD O-RING BOSS FITTINGS: These 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. The male connection is a straight thread with an O-ring. The female port has a straight thread and a machined face to provide a smooth, flat, accurately located surface (minimum spotface), along with a chamfer where the O-ring seats. It seals when the O-ring is compressed into the chamfer when mating the male connection. The O-ring in an O-ring boss fitting seats between the threads and wrench flats, and is positioned around the OD of the male end of the fitting. This allows for a leak-tight seal that is seated against the female port. O-ring boss fittings are either adjustable or non-adjustable. Adjustable O-ring boss fittings are typically elbows or tees that are installed in a fixed direction. Non-adjustable O-ring boss fittings are usually plugs and basic connectors that are fitted into a port without the need for alignment.

FACE SEAL OR FLAT-FACE O-RING (FFOR) FITTINGS: Face seal and flat-face O-ring connections are considered the best for leak control. The male connector has a straight thread and an O-ring in the face. The female has a straight thread and a machined flat face. The seal takes place by compressing the O-ring onto the flat face of the female, similar to a split flange type fitting. The threads maintain the connection mechanically. Choosing O-ring boss or FFOR fittings often depends on the location for wrench clearance. However, flange fittings are mostly used with applications calling for ≥ 7/8” OD tubing or extremely high pressures.

FITTING ADAPTERS: Fitting adapters are used to modify the connection in a hydraulic system to achieve functions such as:

Thread conversion for changing from one port thread type to another, typically for hose or tube fitting connections (i.e. JIC to NPT thread adaptors).
• Stainless-steel O-ring face seal and flange adapters.
• Hose end adaptors to connect hose-to-hose or hose-to-port (port being a female threaded hole in a component).
• Thread size adaptors are used to reduce or increase the existing thread connection.

There are many styles of fittings that serve as adaptors, including:

• Hose barb to male or female pipe, which can be straight, tees, elbows, MAORB (Male Adjustable O-ring Boss) and more.

The system should be designed with consideration of using complementary hoses, couplings, fittings and adaptors to ensure safety, reliability and long service life.

WELD-ON FITTINGS: Hydraulic weld-on fittings (also known as socket weld fittings) have a pipe inserted into the open ID and joined to pipe or other hydraulic fitting types by arc welding fillet-type seals around the perimeter where the fitting flange extends over the pipe. Unlike butt weld fittings which are used for pipe connections up to 10 inches, weld-on fittings are typically used in smaller pipe diameters of up to 2 inches. In addition, performing butt welds has a higher installation cost than using weld-on fittings due to the labor cost and having to use a skilled welder. Weld-on fittings are the best choice for smaller hydraulic system pipe welds where structural strength is important and/or to minimize the chance of leaks.

Common applications for weld-on fittings include:
• All ASME pipe applications
• Hydraulic piping systems that are required to be permanent
• Hydraulic system lines transferring toxic, flammable or sensitive materials where the chance of leaking is prohibited
• Steam lines experiencing up to 600 PSI

The importance of selecting the right hydraulic fitting type cannot be understated. If the hose is capable of handling high pressure, then the weakest link in the system is the connection points. In order to maintain the integrity of the line to ensure it can reach its full capacity, the correct fitting must be selected. Otherwise, a leaking hydraulic line can cause a gradual decline in strength or a catastrophic failure of the system. It is also very important to remember that not all fittings, hoses and other components are necessarily compatible or universal. Though interchangeability with components from different manufacturers is common, and when matched correctly is often safe, there can be differences in designs or specifications. Therefore, each component in the system must be properly selected to ensure a tight seal and system integrity.

This blog is an excerpt from our latest whitepaper, The What, Where & Why of Tube Fittings & Adapters. Click here or below to get your copy!

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