Hydraulic fittings are widely used. You can usually find them in the hydraulic pipelines of excavators, the interface of agricultural tools on tractors, and other places. This article will provide you with all the information about hydraulic fittings.
What is a Hydraulic Fitting？
A hydraulic fitting is a component used to connect various parts of a hydraulic system. It can be connected to hydraulic cylinders, pipes and hydraulic hoses.
Its main function is to ensure the smooth flow of the liquid within the system. At the same time, it can achieve functions such as flow control, direction change, diversion or mixing.
Through an accurate sealing structure, the hydraulic fittings can maintain a tight seal under high-pressure conditions, preventing leakage and ensuring the safe operation of the system.
Types of Hydraulic Fittings
According to the Thread and Sealing Standards
O-Ring Face Seal Hydraulic Fittings（ORFS）
The O-ring face seal hydraulic fitting adopts a face O-ring sealing structure. The O-ring on the male half’s mating face is pressed against the flat sealing surface of the female half and forming a reliable seal. This structure can prevent leakage and is suitable for use in high-pressure and vibration environments.
Its direct-through structure can withstand a pressure of approximately 250 bar at 20°C, the three-way structure can reach 400 bar, and the cross structure can reach up to 630 bar. It can cover from the main pipeline to the complex distribution structure.
If your system involves interfaces of different standards or diameters, the ORFS fittings can also be flexibly combined with reducers or baffles. During long-term use, you need to pay attention to the material of the O-ring and the processing quality of the end face to ensure stable sealing performance.
Hydraulic Fittings JIC
The JIC fittings achieve sealing through 37° metal expansion. The structure is durable and easy to install. At 20°C, JIC fitting can withstand a pressure ranging from 75 to 450 bars, and is suitable for most high-pressure hydraulic systems. It can be compatible with various port standards, including NPT, BSPP, and external thread metric.
Its main body is usually made of steel or stainless steel. You can choose fluorine rubber or nitrile rubber for the sealing rings to meet the requirements of different oils and temperatures.
ISO Hydraulic Fittings
The ISO hydraulic fittings are designed in accordance with international standards. They can be used for quick couplings and high-pressure threaded connections.
ISO 7241 A series is mainly used in the European market and is widely applied to hydraulic fittings in agricultural and forestry equipment. The ISO 7241 B series is more widely used in the North American region and is commonly employed in industrial equipment, chemical fields, and hydraulic applications with higher requirements.
ISO 16028 specifies the dimensions, permissible working pressure, connection methods, and sealing requirements for flat face hydraulic fittings. ISO 14540 specifies the dimensions, structure and performance requirements for hydraulic threaded connection fittings with a working pressure up to 72 MPa.
The advantage of ISO hydraulic fittings lies in their standardisation and interchangeability, which makes it convenient for you to purchase and maintain them across different regions.
O-Ring Boss Hydraulic Fittings (ORB)
The ORB fitting is sealed by means of straight threads and an O-ring at the threaded root. It is easy to assemble and disassemble, and has nice sealing performance. It is commonly used for fixed pipelines such as hydraulic pump bodies, valve blocks and distributors.
The ORB fitting is suitable for medium and high-pressure oil circuits. Its sealing reliability depends on the material of the O-ring and the installation condition. You should choose the appropriate material when it is exposed to high temperatures or in contact with special oils.
NPT Thread Hydraulic Fittings
The NPT fitting achieves sealing through conical threads and sealant. The NPTF fitting undergoes slight deformation during the tightening of the threads to achieve a dry seal between the metals.
They have strong versatility and low cost, which makes them suitable for auxiliary oil circuits or low to medium pressure systems. However, threaded seals are sensitive to vibration and frequent disassembly. They are not suitable for applications requiring zero leakage.
According to the Connection Method
Flanged Hydraulic Fittings
The flange hydraulic fitting is fixed by the flange, bolts and sealing ring, and is suitable for large-diameter, high-flow and high-pressure pipelines.
The SAE code 61 flange fitting is suitable for low-pressure applications with a maximum pressure of no more than 3000 psi. The SAE code 62 flange fitting is suitable for high-pressure applications with a maximum pressure of no more than 6000 psi.
The flange connection makes it convenient for you to disassemble and maintain the system. It is commonly used in large hydraulic stations, main circuits and heavy construction machinery. However, it has a large size and a high cost. You need to control the torque and alignment during installation strictly.
Hydraulic Crimp Fittings
The hydraulic crimping fitting fixes the metal sleeve onto the end of the hose using a dedicated crimping machine to achieve a long-term and reliable connection. It has excellent pressure resistance performance and is suitable for mass production or long-term use.
It requires a crimping device during installation. When you need repairs, it is not as convenient as reusable components.
Reusable Hydraulic Fittings / Hydraulic Quick Connect Fittings.
The reusable hydraulic fittings are also known as hydraulic quick connect fittings. It does not require a special crimping machine. It can be installed or disassembled using a wrench or a vice. It is convenient for quick maintenance and temporary adjustments. The pressure-bearing capacity is limited. You can use it for on-site maintenance, emergency replacement or testing in the system.
According to the Distinction of Structure and Function
Straight Hydraulic Fitting
The straight hydraulic fitting is used for connecting pipes without changing the flow direction. It can be combined with various types of sealing methods. It enables the straightening of hydraulic pipelines or the transition of standardised interfaces.
Elbow Hydraulic Fitting (45°、90°)
The elbow fitting is used to change the flow direction of the fluid and can reduce the space occupied by the piping. The bending radius of the elbow will affect the change in fluid velocity and pressure drop. In high-flow or pulsating pressure situations, you should choose large-radius elbows to reduce energy loss.
The bend section is a stress concentration point. When installing, you must ensure that the position of the pipe clamp is appropriate and that the force on the pipeline is evenly distributed.
Tee Fittings
The tee hydraulic fittings can be used for branching and merging of pipelines. The local flow resistance at the branch point will increase. When using it, you need to consider the allowable pressure drop of the system and the proportion of flow distribution.
Cross Fittings
The cross fitting provides interfaces in four directions and is commonly used in control systems or low-pressure diversion scenarios. For example, the multiple branch circuits around the control valve group. Because it has four connection points, the installation and sealing requirements are quite high.
Reducer Fittings
The reducer fitting is used to connect pipes or hoses of different diameters and enables a smooth connection between the larger and smaller-sized interfaces. When you need to add new components or connect different specifications of hoses in the system, the reducer fitting can quickly achieve size matching and avoid the need to re-route the pipes.
The reducer fitting generally has two structures: concentric and eccentric. It can meet the requirements of smooth transition or reducing fluid turbulence, and is a very commonly used adapter in on-site modifications.
Bulkhead Fittings
The bulkhead fitting is mainly used to allow the pipeline to pass through the tank, box or partition. And it keeps a firm and sealed connection at the perforated area. It can fix the pipeline and also prevent the hose from coming into contact with sharp edges to avoid any damage.
The outer side of the bulkhead fitting is equipped with a locking nut and a sealing gasket, which can prevent liquid from leaking at the plate wall. You can usually use them in places such as the hydraulic power unit, the fuel tank, and the equipment casing.
In addition to hydraulic connectors, many fluid handling systems require compatible brass valves and fittings for water distribution, filtration, and mechanical plumbing applications.
The Materials of the Hydraulic Fittings
Carbon Steel Hydraulic Fittings
Carbon steel is one of the most common materials for hydraulic fittings. It is economical in price and has moderate strength. It is suitable for most conventional hydraulic systems. You can use the carbon steel fittings within the temperature range of -53°C to 260°C.
Its pressure-bearing capacity can meet the requirements of medium and high pressure working conditions. It is a common choice for systems with limited budgets and low corrosion requirements.
Stainless Steel Hydraulic Fittings
The stainless steel hydraulic fittings can operate stably within an extremely wide temperature range of -253°C to 648°C, and can withstand a maximum pressure of approximately 10,000 psi.
Its strength and durability are superior to those of other metal materials. It is very suitable for chemical industries, marine equipment or high-performance industrial hydraulic systems.
If your system is exposed to high temperatures, high pressures or corrosive media, stainless steel joints would be a good choice.
Brazed Hydraulic Fittings
The brass fittings have excellent corrosion resistance and durability, and are commonly chosen for many light and medium-pressure hydraulic systems. Its applicable temperature range is from -53°C to 204°C, and it can withstand a maximum pressure of approximately 3000 psi.
Bronze itself has excellent machinability and rust resistance, and it is also very convenient in equipment maintenance and modification. It is an ideal choice for balancing cost and performance.
Plastic Hydraulic Fittings
The corrosion resistance of plastic fittings is superior to that of metal connectors, but their physical strength and durability are lower. You can use it in low-pressure, low-temperature or in systems with strict weight requirements, such as in the transportation of chemical media or in lightweight equipment.
Although plastic connectors are not suitable for high-pressure or heavy-load conditions, they can extend the service life of the system in corrosive liquid environments.
Aluminium Hydraulic Fittings
Aluminium fittings are relatively rare and are mostly used in specific fields. It is lighter than steel joints and has nice corrosion resistance. It is commonly used in hydraulic applications such as in automobiles and transportation systems where weight reduction is required.
Aluminium material performs stably in medium and low pressure environments. You can use it in scenarios where weight sensitivity and corrosion resistance are high requirements. But its strength and pressure-bearing capacity are inferior to steel or stainless steel fittings.
What Factors need to be Considered when Choosing a Hydraulic Fitting?
Connection Dimension
When you are choosing a hydraulic fitting, size compatibility is the primary factor to consider. The nominal size of the fitting and the inner diameter of the fluid passage will affect the flow rate and pressure drop of the system.
If the inner diameter is too small, the flow of your hydraulic oil will be restricted. This will result in energy loss and a decrease in system efficiency. A large inner diameter may lead to installation difficulties or poor sealing.
You need to select the appropriate hydraulic fittings based on the specifications of the pipe or hose, and also take into account the size limitations imposed by different types of hydraulic fittings.
Preassure
When choosing a hydraulic fitting, you should consider the rated pressure and also leave a margin for safety factors. Your hydraulic fitting should be capable of withstanding the maximum working pressure of the system as well as any sudden pressure surges.
A lack of pressure in the hydraulic fitting may cause leakage in the pipeline. We suggest that you assess the pressure-bearing capacity of the connector based on the actual system load to ensure long-term stable operation.
Operating Environment
In hydraulic systems, the working environment has a significant impact on the lifespan of the fittings. If your operating environment is in high temperatures, low temperatures, corrosive media or frequent vibrations, the selection of hydraulic fitting materials and seals becomes particularly important.
You should select the hydraulic fittings that can withstand the actual temperature range and have anti-corrosion properties. This is to ensure that your system remains stable and reliable in various environments.
Connection Mode
You need to consider whether the hydraulic fitting needs to be frequently disassembled and reassembled. If your system requires frequent connections and disconnections, the hydraulic quick connect fittings can significantly save your time and maintenance costs.
For long-term fixed installation, you can choose the hydraulic crimp fitting. It also offers a higher pressure-bearing capacity.
In addition, you also need to consider whether to choose metric hydraulic fittings or inch hydraulic fittings.
The Advantages of Hydraulic Fittings
High Efficiency
The design of hydraulic fittings can improve the efficiency of pipe connections in hydraulic equipment. Especially for the hydraulic quick connect fittings, you can complete the connection and disconnection of the pipelines without using complex professional tools. For instance, when you are replacing the hydraulic hammer in an excavator or the hydraulic moulds in a production line, the hydraulic quick connect fitting can save you a lot of time.
Furthermore, many hydraulic fittings have a 360° rotation function, which solves the problem of aligning the threads during installation. This simplifies the operation process and avoids damage to the hose caused by forced alignment. It provides a guarantee for the long-term stable operation of the system.
High Sealing Performance
The hydraulic fitting maintains excellent sealing performance under various working conditions. Its advanced sealing structure and high-quality sealing materials can withstand high-pressure impacts and continuous vibrations.
The hydraulic fitting can automatically seal the oil circuit when disconnected. This design prevents hydraulic fluid leakage and blocks external contaminants from entering the system.
Excellent Durability and Environmental Adaptability
Hydraulic fittings are made of high-strength materials and with special surface treatment processes. They can withstand harsh conditions such as moisture and corrosive media.
The optimised locking mechanism can effectively resist the high-frequency vibrations generated during the operation of the equipment. This ensures that the connection points remain stable for an extended period.
You can use it in heavy-load application scenarios such as construction machinery and mining equipment. It will provide a durable and reliable connection guarantee for the equipment.
Easy Maintenance
Many easily damaged components such as seals and clamps in hydraulic fittings are standard parts that can be replaced separately. When the sealing effect decreases, you don’t need to replace the entire hydraulic fitting; just replace the sealing. Even for hydraulic crimp fittings, their structure is usually easy to install and disassemble.
The Application of Hydraulic Fittings
Engineering Machinery
In excavators, bulldozers and loaders, hydraulic hose fittings are used to connect hydraulic cylinders, pumps and valves. It keeps the hydraulic oil flows stable under high pressure and controls the mechanical movements precisely.
Industrial Manufacturing
Hydraulic fittings are used in injection moulding machines, presses, machine tools and automated assembly lines. It helps the pipeline to achieve diversion, mixing, or directional adjustment and makes the hydraulic system operate efficiently and reliably.
Agricultural Machinery
Hydraulic fittings can be used in tractors, harvesters and sprinkler irrigation equipment. They can withstand vibrations and dust in the working environment. At the same time, they ensure the sealing and stability of the hydraulic system during operation.
Transportation
Hydraulic fittings are commonly used in the braking systems, steering systems and lifting mechanisms of vehicles. It ensures the safe transmission of fluids under high-frequency operation.
FAQ
How to Prevent Hydraulic Fittings from Loosening in a Vibrating Environment?
You can choose hydraulic fittings with locking nuts, double-thread locking or O-ring compression designs. When installing, you should make sure that the threads are tightened to the recommended torque. In high-vibration systems, you can also use lock washers or flexible piping to reduce the transmission of vibrations to the fittings.
Will Hydraulic Fittings Fail after Long-Term Standing?
If the system is not working for a long time, the seals may lose their sealing performance due to ageing, cracking or reacting with the oil. For equipment that has been out of service for a long time, you should regularly inspect the hydraulic fittings and seals. And conduct a pressure test before reactivating it.
Is it Necessary to Use Teflon Tape on Hydraulic Fittings?
In most cases, we do not recommend the use of Teflon tape on the high-pressure threaded connections of hydraulic fittings. The Teflon tape may peel off between the threads and forming debris that could clog the oil passage or damage the equipment. Its thickness will lead to uneven force distribution and reduce the reliability of sealing. It also affects torque control, which will cause over-tightening or over-relaxation.
How to Install Hydraulic Hose Fittings？
First of all, make sure your system is completely depressurised to avoid any danger caused by residual hydraulic pressure during the operation. Use specialised tools to cut the pipe smoothly and remove burrs and debris. Then you need to clean the area around the hose connection.
Next, you can apply an appropriate amount of hydraulic oil or lubricant to the hydraulic hose fitting and the pipe end to facilitate insertion. You can mark with a marker pen to confirm whether it is fully inserted.
For the hose crimping fittings, you need to use a dedicated crimping machine for the connection. After crimping, check whether the crimping ring meets the specifications.
Final Thoughts
Target Hydraulics has advanced CNC machining technology, which can achieve one-time moulding of hydraulic fittings. This can ensure the consistency and accuracy of hydraulic fittings and improve the durability and sealing performance of the product.
We can offer a wide range of standard hydraulic fittings to meet the requirements of general hydraulic systems. If you have any special requirements, we also offer customised services. Welcome to contact us!
