Hydraulic hose fittings connect hydraulic hoses to valves, pumps, motors, cylinders and other components. Choosing the right fit is critical, as incorrect connections can lead to leaking hydraulic fluid and potentially costly equipment or safety issues.
When selecting hydraulic hose fittings, size, temperature, application and material/media are all important considerations. Flanges and fittings both provide an excellent connection, but deciding which type is best for your application depends on many factors.
All-Metal Fittings
Brass is a common fitting material that provides many benefits. It’s malleable and easier to shape than other metals, which reduces labor costs for trade professionals. It also resists corrosion well.
The all-metal construction of a push fit provides superior strength, making it ideal for high-pressure applications. The one piece ferrule is either asymmetrical or symmetrical to ensure it seals evenly around the tubing’s OD. Asymmetrical ferrules are cone shaped and can only be inserted into the body in one direction, while symmetrical ferrules look like two cones back-to-back.
These types of fittings require less torque to install, and the elastomeric seal absorbs small amounts of movement and vibration. This flexibility increases the lifetime of the fitting, while preventing leaks caused by rigidity and stress. Typical configurations include bushings, caps, couplings, elbows, and crosses. Each type of fitting works with a specific size of pipe or tube. It’s important that the tube is clean and free of imperfections, as these can cause leaking past the ferrule.
Flare Fittings
When used with ductile copper, aluminum or soft steel tubing, flare fittings can create a strong, leak-tight connection. They can also be connected to other types of fittings (elbows, union, tees and crosses). Flare connections require the tubing to be flared prior to assembly, which is done by inserting a tool into the tube end and applying pressure while the tube cools. The resulting cone-shaped surface makes an extremely tight seal that can be removed only by deforming the tube.
A wide variety of sizes are available. It is important to ensure that the tubing diameter and the flare fitting size are compatible. Over- or under-sized fittings are prone to leaks and failure. Like all fittings, they should be compatible with the hydraulic fluid and be rated for the operating temperature range. They should also be compatible with the maximum operating pressure for the system. Pressures above or below the design rating will cause them to fail, possibly resulting in system failure.
Flareless Fittings
Flareless fittings are a great alternative to flared fittings and are best used in high-pressure hydraulic designs. These fittings are composed of a nut, a single or twin ferrule and a fitting body. When the nut is tightened, it compresses the ferrule against the tube’s OD and creates a strong and leak-free seal. Flareless fittings can be used on thin-to medium-wall tubing and perform well in the presence of operating pressures of up to 3 ksi.
The advantage of using a flareless fitting is that its design eliminates the need to flaring the tubing, which reduces the chance for nicks and cuts that can damage the inner wall of the tube. In addition, the single bite of a flareless ferrule offers superior shock absorption and provides visual cues that allow users to inspect for a good fit prior to system pressurization. The only drawback to using these fittings is that they require a pre-set process to ensure correct function.
O-Ring Fittings
SAE straight thread O-ring boss fittings (ORB), also known as face seal hydraulic fittings, are a solution for eliminating leaks in medium to high pressure hydraulic applications. These fittings utilize an O-ring to provide a metal-to-metal seal at the interface between the male and female port connection.
O-ring face seal fittings are commonly used in hydraulic systems found on off-road construction and agricultural equipment such as tractors, combines and skid steers. These systems often experience higher operating pressures and harsh mechanical shocks than other hydraulic applications and are more prone to fluid leaks due to vibration and thermal cycling.
The O-ring in these fittings provides a more reliable seal than traditional metal hydraulic couplings, which can be subject to excessive torque, stripping and cracking components and causing leaks. To prevent leakage, these fittings should always be installed with the O-ring lubricated with the system’s hydraulic fluid. This reduces the coefficient of friction between the flange nut and the threaded portion of the male or female port and allows for tightening with a wrench.
