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Flareless compression fittings are used to terminate hydraulic tubing ends or allow them to connect to other hydraulic tubing. They come in straights, 90 degree elbows, 45 degree elbows, tees, branch tees, run tees and crosses.

Dual Ferrule versus Single Ferrule

Most compression tube manufacturers will use dual or single ferrule configuration to lock tubing to the fittings. Swagelok, Parker, SSP, and Weatherhead flareless compression fittings will use a dual ferrule combination whereas Tylok and Tompkins will use a single ferrule combination.
  • Dual Ferrule Compression Tube Fittings


    Photo of Stainless Steel Dual Ferrule Fitting on white background
    Leaks in hydraulic hoses can be expensive and dangerous. Slow leaks cause slippery surfaces and compromise the efficiency of equipment, while large leaks can shut down an entire job site. Many leaks and equipment failures occur at the fitting site. This is why it is important to always use the proper fittings with each hose type. The fittings should be installed correctly and checked regularly.


    A dual ferrule tube fitting is often preferred over a single ferrule. A dual-ferrule fitting has 4 parts that, when combined with the tube itself, create a 5-part joint that is more likely to remain leak-free.

    These four pieces are the nut, a front and back ferrule, and the body of the fitting. The ferrules attach to the outside of the tube, creating a firm grip when the nut is tightened without collapsing the inner tube. This allows the installer to tighten the nut fully, ensuring a tight seal.

    Some fittings are constructed to eliminate torque as the fitting is installed. This lessens potential damage to the hose itself. The ferrule configuration also helps to overcome some variance in tube thicknesses, although care should still be taken to match hydraulic hoses as closely as possible.


    High-quality dual-ferrule tube fittings will be reliable in all of the same environmental and work-site conditions as the hoses themselves.


    Dual-ferrule tube fittings should be able to resist fluctuations in temperatures caused by environmental variance as well as from heat created by machinery. The seal should hold steadily at whatever temperatures the hoses are rated for. As the temperature cycles, the seal should remain steady.


    Many hydraulic hoses are used under fluctuating pressures, with occasional bursts of high pressure. Failure of a fitting at this stage can be catastrophic. Dual-ferrule tube fittings should outlast the hoses themselves, resisting any pressure. The tube should burst before the fitting does. They should not be compromised no matter how many times they are pressurized and then released.


    Despite your best efforts, there will be some differences in the hoses joined by fittings. A good fitting will be able to seal properly regardless of minor variables in tube construction and materials. It should also be able to seal properly without crushing the tube or compromising the flow of fluids.

  • Single Ferrule Compression Tube Fittings


    Single ferrule compression tube fittings are used in hydraulics and instrumentation. The design of the single ferrule fitting should result in a leak-proof seal that resists wide fluctuations in temperature and pressure and can resist vibration and torque. Single ferrule fittings are available in a variety of materials, and should be matched properly with the hydraulic hoses to which they will be joined.


    The single ferrule compression tube fitting can be used in many industries, including:
    • Petro-chemical
    • Pulp and paper
    • Chemical
    • Power
    • Nuclear


    The single ferrule compression tube fitting is easily installed and creates a leak-proof seal. The single ferrule has almost a spring-like function that keeps tension between the body of the fitting and the compression nut. These fittings should be able to withstand the same demands as the hydraulic hoses to which they are attached. They should also outlast the hoses when installed correctly.


    Temperature fluctuations on the job site can cause wear and tear on equipment. Environmental factors, along with heat generated by hydraulic fluids and machinery, can cause hydraulic hoses to harden and become more brittle over time. This can affect the seal at fittings.

    Single ferrule compression tube fittings will last until you have to replace the hose, and usually can be installed on the new hoses. As temperatures at the job site fluctuate, the fitting should remain effective.


    Pressure within the hydraulic hose will fluctuate with temperatures and because of pressure from machinery. Single ferrule fittings will maintain a firm seal without compromising the hose. At this point, it is important to note that the correct fitting must be selected for each hose so that a proper seal can be established and maintained. Fittings that are too big or too small for a particular hose will not withstand the rigor of a job site, and can contribute to catastrophic failure.


    If a single ferrule fitting is approved for two different hoses, then it will be adaptable to both hoses. This will work even if one hose is fractionally a different size than the other hose, or has a different structure within approved variances. The fitting should be able to provide a tight seal without crushing the hose or impeding flow.

  • Stainless Steel Compression Tube Fittings


    Stainless steel compression tube fittings are chosen in many different industry settings, due to their durability and quality service.

    There are many other materials available for compression tube fittings. However, stainless steel is one of the least expensive yet durable materials used in any sector. It withstands corrosion from various chemicals, is impervious to temperature fluctuations, and maintains proper seals under pressure.


    Stainless steel fittings are so durable that they are often used over and over again, through several sets of hoses. If a fitting is damaged in some way, it should, of course, be discarded. However, stainless steel is used for such a wide variety of processes because it will ensure there is no leakage, regardless of pressure or temperature.

    In addition, when properly cleaned stainless steel fittings can be used for different hydraulic materials without fear of failure. As long as the fitting is functioning properly, it can be reused for any approved mechanical, chemical, or industrial use.


    Corrosion can be a serious issue in some applications. Various chemicals are often present and can corrode joints and the interior of non-approved fittings. Stainless steel fittings are more resistant to corrosion due to passivation; a vital process enhancing their corrosion resistance. This involves treating the steel with an acid solution, creating a thin protective oxide layer ensuring durability that often outlasts even the hydraulic hoses.


    Hydraulic hoses are manufactured within certain parameters relating to the type of fluids or gasses they will be transported. They are also manufactured to withstand pressure from pumps, compressors, and other machinery that propel the fluid or gas.

    Stainless steel fittings are ideal for handling the ranges of pressure delivered by tools and machinery. Whether the pressure is steady or fluctuating, the fitting will probably last longer than the hose under various pressure conditions.

    Burst pressure may be a problem for some brands of hoses, but stainless steel fittings should be just fine under burst conditions and vacuums as well.

    Vibration while under pressure may cause the failure of some materials, but the stainless steel fitting will remain dependable when installed properly.


    You can order most stainless steel compression tube fittings according to the desired gauge. You will need to refer to guides to make sure you select an approved gauge for the tube and processes you use. Most of the fittings are high-quality enough that the threads will work properly without galling. The fittings usually install easily and provide a good seal.