Whether in ordinary industrial scenarios or under corrosive and high-pressure vibration conditions, high-quality hydraulic tube fittings are always the key support for transmitting power in hydraulic systems.
This post will comprehensively explain hydraulic tube fittings from aspects such as type, material, selection, and installation. We hope this will help you make the most appropriate choice.
What is a Hydraulic Tube Fitting?
A hydraulic tube fitting is a key connecting component in hydraulic systems. It can connect tubes or join hydraulic components, such as hydraulic pumps, valves, and hydraulic actuators together.
The Function of Hydraulic Tube Fittings
The hydraulic tube fittings can construct a sealed and stable fluid transmission channel, which allows hydraulic media to flow without leakage. At the same time, it can maintain stable system pressure and resist the effects of vibrations and temperature fluctuations in the working conditions.
Types and Applications of Hydraulic Tube Fittings
Threaded Hydraulic Tube Fittings
The threaded hydraulic tube fitting is connected through a combination of internal and external threads. It is widely used in low-pressure tubes and ports for connecting pumps, valves, and other components. It is suitable for situations that require frequent disassembly.
According to different thread standards, it is mainly divided into the following types.
NPT and NPTF
This is a hydraulic tube fitting that complies with American standards. The NPT hydraulic tube fitting is a 60° tapered tube thread. It cannot achieve complete sealing on its own and requires the use of Teflon tape or sealant during installation.
The NPTF hydraulic tube fitting is an upgraded version of NPT. It is a dry-sealed tapered tube thread, which can provide better sealing performance without the need for sealing materials.
BSPP and BSPT
This is a hydraulic tube fitting that complies with British standards. The BSPT hydraulic pipe joint is a 55° sealed conical tube thread. It can achieve preliminary sealing through deformation during thread tightening. In practical applications, you need to use sealant to further enhance the sealing reliability.
The BSPP hydraulic tube fitting has parallel threads. It does not have the ability to seal independently. You need to use sealing gaskets or O-rings to achieve sealing.
Metric Hydraulic Tube Fittings
The metric hydraulic tube fittings use standard thread dimensions measured in millimeters. It complies with international standard practices. The metric hydraulic tube fittings achieve reliable sealing by using different sealing gaskets or O-rings.
Flared Hydraulic Tube Fittings
The flared hydraulic tube fitting is to first expand the tube opening into a specified cone angle. Then it is tightly combined with the conical surface of the joint to form a metal-to-metal sealing structure.
The flared hydraulic tube fitting usually does not require seals. It has high connection strength and is convenient for disassembly and assembly. It is suitable for applications where strong vibrations and large pressure fluctuations may occur, such as engineering machinery, shipbuilding, and industrial hydraulic systems.
JIC 37°
The JIC 37° flared hydraulic tube fitting is the most widely used flared hydraulic tube fitting in global hydraulic systems. It follows SAE J514 and ISO 8434-2 standards. The 37 ° cone angle structure achieves a good balance between sealing and vibration resistance.
SAE 45°
The SAE 45° flared hydraulic tube fitting complies with the SAE J512 standard and adopts a 45° cone angle. Its design is simpler and more commonly used in low-pressure fluid transport scenarios, such as low-pressure tubes in refrigeration equipment.
Hydraulic Tube Compression Fittings
The hydraulic tube compression fitting is also known as the bite-type hydraulic tube fitting. It is composed of three parts: the fitting body, the ferrule and the nut.
When tightening the compression nut, the sleeve will be pushed forward and deformed. The ferrule will bite into the outer wall of the tube and adhere tightly to the fitting body. This will create a double-sealed structure.
DIN 2353 and ISO 8434-1 are the most widely used and standardized specifications for hydraulic tube compression fittings in worldwide. It usually has excellent high and low temperature resistance, corrosion resistance, and can be used for transporting oil, gas, and general corrosive media.
The hydraulic tube compression fittings are commonly used in industrial hydraulic systems, marine hydraulic systems, and aerospace hydraulic instrument tubes. Under high pressure and strong vibration conditions, it can maintain a stable sealing effect.
O-Ring Sealed Hydraulic Tube Fittings
The O-ring sealed hydraulic tube fitting is an elastic seal. It blocks the leakage channel by compressing the O-ring to produce deformation. The sealing performance of the O-ring sealed hydraulic tube fitting is better than that of the ordinary threaded seal, and it also has certain fault tolerance. It can compensate for the minor flaws of the sealing surface and is suitable for medium and high-pressure hydraulic systems.
ORB
The ORB hydraulic tube fitting adopts a straight thread structure. The O-ring is installed in the cylindrical groove inside the threaded part. When the thread is tightened, the end face of the fitting presses the O-ring to achieve sealing.
The ORB hydraulic tube fitting has a compact structure and is suitable for installation scenarios with limited space. You can use it to connect the processing oil ports of hydraulic pumps, hydraulic valves, hydraulic cylinders and other components.
ORFS
The O-ring of the ORFS hydraulic tube fitting is installed in the flat end face groove. When the two mating planes are fastened together, the O-ring is uniformly flattened within the sealing cavity.
The ORFS hydraulic tube fitting has extremely strong resistance to vibration and pressure pulses. If you are looking for a leak free hydraulic system, then it will be your preferred type of fitting. ORFS hydraulic tube fittings are widely used in high-pressure and high-vibration hydraulic circuits of heavy construction machinery and construction equipment.
Flanged Hydraulic Tube Fittings
The flanged hydraulic tube fitting achieves pipe connection by fastening the separate flange plates with bolts. There is a sealing gasket in the middle. The flanged hydraulic tube fitting has a large sealing area and can withstand extremely high system pressure and large flow rate fluid transportation requirements.
You can use it in large diameter hydraulic tubes, such as main hydraulic tubes in large hydraulic presses, mining machinery, ship deck machinery, and steel metallurgy equipment.
The Materials of the Hydraulic Tube Fittings
Carbon Steel
Carbon steel is the most commonly used material in hydraulic tube fittings. It has high strength and good mechanical processing performance, and can withstand high-pressure working conditions in hydraulic systems.
Carbon steel has weak corrosion resistance and is prone to rusting in humid, dusty, or chemical environments. It is more suitable for dry indoor industrial environments, such as the hydraulic systems of ordinary machine tools and the hydraulic tubes of general machinery.
We usually perform surface treatments such as galvanizing and painting on carbon steel hydraulic tube fittings to enhance their rust prevention ability.
Stainless Steel
The stainless steel hydraulic tube fitting is corrosion-resistant and has good mechanical strength and processing performance. It can maintain stable performance in various complex environments.
304 Stainless Steel
304 stainless steel is a basic chromium-nickel alloy with excellent corrosion resistance. And it is non-magnetic, has good hygiene, and will not contaminate the fluid.
304 stainless steel hydraulic tube fittings have a moderate cost and are commonly used in scenarios such as food processing equipment and light industry hydraulic tubes that require certain cleanliness and corrosion resistance.
316 stainless steel adds the molybdenum element on the basis of 304. Its corrosion resistance and high-temperature resistance are even better. It can adapt to a wide temperature range of -270℃ to 450℃.
316 Stainless Steel
The 316 stainless steel hydraulic tube fittings are commonly used in marine engineering hydraulic systems, hydraulic tubes of chemical equipment, hydraulic devices of ships, and tubes for transporting highly corrosive media.
Although the cost of 316 stainless steel hydraulic pipe joints is relatively high, it can prevent fitting failure caused by corrosion and reduce long-term use risks.
Brass
The brass hydraulic tube fitting has good corrosion resistance and conductivity. It is easy to machine and shape, with a high degree of sealing surface adhesion. Its cost is between carbon steel and stainless steel.
The mechanical strength of brass is usually lower than that of steel. Therefore, brass hydraulic tube fittings are more commonly used in hydraulic systems with medium and low pressure, lubrication tubes, or instrument pneumatic systems.
Aluminium Alloy
The aluminum alloy hydraulic tube fitting is lightweight while also having sufficient strength and corrosion resistance. It can reduce the overall weight of your device and lower energy consumption.
Aluminum alloy hydraulic tube fittings are particularly suitable for hydraulic systems that are sensitive to weight, such as mobile construction machinery, aerospace hydraulic equipment, and small hydraulic tools.
Factors to Consider when Choosing Hydraulic Tube Fittings
Working Pressure
When selecting hydraulic pipe fittings, you need to first confirm the maximum working pressure of the hydraulic system. The rated working pressure of the hydraulic tube fitting must be higher than the maximum working pressure of the system and should also leave a sufficient safety margin.
For working conditions with frequent pressure fluctuations or impacts, you should choose a structure with stronger shock resistance, such as the hydraulic tube compression fittings or flanged hydraulic tube fittings.
Working Medium
The characteristics of the fluid medium determine the material selection of hydraulic tube fittings and seals.
For example, if you are using ordinary hydraulic oil as the medium, fittings made of carbon steel or 304 stainless steel can be adapted. If the medium is an acid, alkali or other highly corrosive fluid, then 316 stainless steel hydraulic tube fittings must be selected.
For the sealing material, if you are dealing with petroleum-based media, you can choose nitrile rubber seals. You can choose fluororubber seals when exposed to high temperatures or chemical media.
Connection Method and Interface Standards
The size and connection method of the hydraulic tube fitting must be fully compatible with the interface types of your tubes and hydraulic components. You need to clarify the standards and connection methods used in your system.
Environmental Factor
Your working environment will influence the selection of the material and structure of the hydraulic tube fittings. If you want to use it in humid, dusty or outdoor conditions, you can choose carbon steel connectors that have undergone anti-corrosion treatments such as galvanization or painting. Or you can directly choose stainless steel connectors.
In high corrosion environments such as the ocean, you can choose 316 stainless steel material. If there is continuous vibration in the system, it is necessary to select ORFS hydraulic tube fittings with strong vibration resistance or fittings with vibration damping structures.
How to Install the Hydraulic Tube Fittings?
Preparation before Installation
- Cleaning and Inspection:You should thoroughly clean all joint components, threads, and pipe ends to remove burrs, metal debris, oil stains, or rust proof coatings. Meanwhile, check whether the joints, seals and tubes have any deformation or wear.
- Tube handling:Then, you can use a dedicated tube cutting tool to cut the tube to the desired length. The cut must be smooth and perpendicular to the centerline of the tube. After cutting, don’t forget to remove the burrs on the inner and outer edges of the tube end.
General Installation Steps
- Step 1:Align the tube and the joint interface accurately to avoid tube distortion or deviation.
- Step 2:Use your hands to tighten the fitting until the sealing surfaces are in contact. Make sure that the fittings fit smoothly without any jamming.
- Step 3:Use a torque wrench to complete the final tightening according to the torque values specified by the manufacturer. It is strictly prohibited to over-tighten by hand. This may cause thread slippage, sealing surface deformation, or pipeline overload damage.
Key Installation Points for Different Types of Hydraulic Tube Fittings
- Threaded hydraulic tube fittings:For NPT, BSPT and other tapered hydraulic tube fittings, you should evenly apply an appropriate amount of thread sealant or wrap PTFE sealing tape around the threads. The winding direction of the tape is the same as the tightening direction of the screw.
- Flared Hydraulic Tube Fittings:You need to use a special expansion tool to enlarge the end of the tube to a smooth expansion surface that matches the taper of the fitting. Make sure there are no cracks or burrs.
- Hydraulic tube compression fittings:You should insert the nuts and ferrules into the tube in sequence. Make sure that the blade of the ferrule is facing towards the direction of the fitting body.
- O-ring sealed hydraulic tube fittings:You can apply a small amount of clean hydraulic oil lubrication on the surface of the O-ring to facilitate installation and improve the sealing effect.
- Flanged hydraulic tube fittings:First, secure the flange to the tube, and then insert the O-ring or sealing gasket into the flange groove. Next, align the bolt holes of the two flanges, insert the bolts, and then evenly tighten the nuts using an alternating diagonal tightening method. This operation is to keep even force distribution on the flange surface and prevent leakage caused by local gaps.
Check
After the installation of the fitting is completed, you can observe whether the fitting is connected to the tube straight and without distortion. Then, you can conduct a system pressure test to observe whether there is any leakage at the connection point.
At the same time, check whether the tubes and hydraulic tube fittings have any abnormal deformation or noise. After confirming that there are no issues, this hydraulic tube fitting can be used normally.
FAQs
What are the Differences between Hydraulic Tube Fittings, Hydraulic Pipe Fittings and Hydraulic Hose Fittings?
Hydraulic tube fittings are used to connect rigid metal pipes to system components. They are suitable for high-pressure applications and require precise fluid transmission.
Hydraulic pipe fittings are used to connect larger diameter or fixed pipelines. It is commonly found in long-distance or fixed installation pipelines.
Hydraulic hose fittings are used to connect flexible hoses. It can absorb vibrations and compensate for displacements. It is commonly found in mobile devices.
Can Hydraulic Tube Fittings of Different Standards be Interchanged?
No. There are significant differences in the thread form, sealing method, and joint angle of hydraulic tube fittings of different standards. Using incompatible standards of hydraulic tube fittings haphazardly will result in poor sealing or damage to the threads.
If you have to connect different standard fittings, you should use a standard conversion adapter to connect the two incompatible interfaces.
What are the Possible Reasons for the Leakage of Hydraulic Tube Fittings after Installation?
Common causes include aging or damage of the seals, and the failure to tighten the joint threads to the specified torque. During installation, the sealing surfaces are not aligned properly, which leads to uneven force distribution and subsequently causes leakage.
If your hydraulic tube fitting does not match the tube or component interface, it will also cause leakage.
How to Solve the Looseness of Hydraulic Tube Fittings during Use?
First, you need to check whether the installation torque meets the standard. If the torque is insufficient, it is necessary to use a torque wrench to re-tighten it to the specified value.
If the loosening is caused by system vibration, you can install anti-loosening devices or replace the vibration-resistant connectors. Fitting wear can also lead to looseness. You need to replace it in time.
Final Thoughts
An appropriate hydraulic tube fitting is not only related to the sealing and safety of the tube, but also affects the operating efficiency and maintenance cost of the equipment. If you are making decisions regarding selection or procurement, please feel free to contact us. We can provide you with various standard customized hydraulic tube fittings to help your hydraulic system achieve optimal performance.
