A compression fitting is a fitting used in plumbing and electrical conduit systems to join two tubes or thin-walled pipes together. In instances where two pipes made of dissimilar materials are to be joined (most commonly PVC and copper), the fittings will be made of one or more compatible materials appropriate for the connection. Compression fittings for attaching tubing (piping) commonly have compression rings, called ferrules (American English) or olives (British English), in them, and are sometimes referred to as flareless fittings. There are also flare fittings that do not require ferrules/olives.
Compression fittings are used extensively in hydraulic, gas, and water systems to enable the connection of tubing to threaded components like valves and tools.[1] Compression fittings are suited to a variety of applications, such as plumbing systems in confined spaces where copper pipe would be difficult to solder without creating a fire hazard, and extensively in hydraulic industrial applications. A major benefit is that the fittings allow easy disconnection and reconnection.
Operation principle
In small sizes, the compression fitting is composed of an outer compression nut and an inner compression ring (ferrule) that is typically made of brass, copper, or steel. Ferrules vary in shape and material but are most commonly in the shape of a ring with beveled edges. To work properly, the ferrule must be oriented correctly, in the case of copper olives they are normally barrel shaped and this means they cannot be fitted incorrectly, but where this is not so, particularly in Hydraulic and high pressure applications, the ferrule is fitted such that the longest sloping face of the ferrule faces away from the nut.
Fitok tube fittings
When the nut is tightened, the ferrule is compressed between the nut and the receiving fitting; causing both ends of barrel shaped copper olives to be clamped around the pipe when the middle of the ferrule bows away from the pipe, in the case of hydraulic style ferrules they currently have one end which is larger with a 45 degree chamfer which tapers away (from installation contact with the nut) and the small end generally has two internal biting edges, for applications demanding much higher pressure, that penetrate the outside diameter of the tube, the fittings must be tightened to guidelines as per DIN2353 as not to exceed the elastic limit of the steel ferrules, The result is that the ferrule seals the space between the pipe, nut, and receiving fitting, thereby forming a tight joint. The clamping support of the pipe by the force at the taper at both ends help prevent movement of the pipe in the fitting, but it is only the taper at the receiving fitting itself that needs to seal completely, since if it does seal (to both the pipe and the compression fitting) then no fluid can get to the nut threads or the taper at the nut end to result in any leaks. As a result some similar fittings can be made using an olive with only one taper (or a fixed cone sealed to the pipe) where the sealing at that taper prevents fluid from reaching the nut.
Larger sizes of compression fitting do not have a single nut to compress the ferrule but a flange with a ring of bolts that performs this task. The bolts have to be tightened evenly.
Thread sealants such as joint compound (pipe dope or thread seal tape such as PTFE tape) are unnecessary on compression fitting threads, as it is not the thread that seals the joint but rather the compression of the ferrule between the nut and pipe. However, a small amount of plumber's grease or light oil applied to the threads will provide lubrication to help ensure a smooth, consistent tightening of the compression nut.
It is critical to avoid over-tightening the nut or else the integrity of the compression fitting will be compromised by the excessive force. If the nut is overtightened the ferrule will deform improperly causing the joint to fail. Indeed, overtightening is the most common cause of leaks in compression fittings. A good rule of thumb is to tighten the nut first by hand until it is too difficult to continue and then tighten the nut one half-turn more with the aid of a wrench; the actual amount varies with the size of the fitting, as a larger one requires less tightening. The fitting is then tested: if slight weeping is observed, the fitting is gradually tightened until the weeping stops.
The integrity of the compression fitting is determined by the ferrule, which is easily prone to damage. Thus care should be taken when handling and tightening the fitting, although if the ferrule is damaged it is easily replaced.
Types of fittings
There are two types of compression fitting, standard (British type-A/non-manipulative) and flare fittings (British type-B/manipulative). Standard fittings require no modifications to the tubing. Flare fittings require modification of the tubing with a special tool. Standard fittings are typically used for water, hydraulic, and compressed air connections, whereas flare fittings are used for gas and high pressure lines.
A standard fitting can be installed using an ordinary wrench to tighten the surrounding nut. To remove it, a specialized puller is often used to slide the nut and ferrule off the tube. If the ferrule is difficult to remove it can be weakened with a cut, care being taken to not nick the pipe while cutting.
Advantages
Compression fittings are popular because they do not require soldering, so they are comparatively quick and easy to use. They require no special tools or skills to operate. They work at higher pressures and with toxic gases. Compression fittings are especially useful in installations that may require occasional disassembly or partial removal for maintenance etc., since these connections can be broken and remade without affecting the integrity of the joint. They are also used in situations where a heat source, in particular a soldering torch, is prohibited, or where it is difficult to remove remains of water from inside the pipe which prevent the pipe heating up to allow soldering.
Disadvantages
Compression fittings are not as robust as soldered fittings. They are typically used in applications where the fitting will not be disturbed and not subjected to flexing or bending. A soldered joint is highly tolerant of flexing and bending (such as when pipes knock or shake from sudden pressure changes e.g. caused by water hammer). Compression fittings are much more sensitive to these type of dynamic stresses. They are also bulkier, and may be considered less aesthetically pleasing than a neatly soldered joint. Compression fittings work best when tightened once and not disturbed.[contradictory] Some compression connectors may never be reused, such as a ferrule ring type. It can never be reused once they have been compressed. This connector is directly placed over the pipe and the nut is tightened compressing the ferrule between the pipe and the body of the fitting. Compression of this ferrule also results in deformation of the copper tubing. If a compression type connection needs to be redone, more often than not the compressed copper/ferrule would need to be cut off and a new ferrule is to be used on a clean non-compressed piece of pipe end. This is to assure a leak proof sound connection.
Plumbing is any system that conveys fluids for a wide range of applications. Plumbing uses pipes, valves, plumbing fixtures, tanks, and other apparatuses to convey fluids. Heating and cooling (HVAC), waste removal, and potable water delivery are among the most common uses for plumbing, but it is not limited to these applications. The word derives from the Latin for lead, plumbum, as the first effective pipes used in the Roman era were lead pipes.
A ferrule is any of a number of types of objects, generally used for fastening, joining, sealing, or reinforcement. They are often narrow circular rings made from metal, or less commonly, plastic. Ferrules are also often referred to as eyelets or grommets within the manufacturing industry.
A gasket is a mechanical seal which fills the space between two or more mating surfaces, generally to prevent leakage from or into the joined objects while under compression. It is a deformable material that is used to create a static seal and maintain that seal under various operating conditions in a mechanical assembly.
American National Standard Pipe Thread standards, often called national pipe thread standards for short, are United States national technical standards for screw threads used on threaded pipes and pipe fittings. They include both tapered and straight thread series for various purposes, including rigidity, pressure-tight sealing, or both. The types are named with a full name and an abbreviation, such as NPT, NPS, NPTF, or NPSC.
Hydraulic machines use liquid fluid power to perform work. Heavy construction vehicles are a common example. In this type of machine, hydraulic fluid is pumped to various hydraulic motors and hydraulic cylinders throughout the machine and becomes pressurized according to the resistance present. The fluid is controlled directly or automatically by control valves and distributed through hoses, tubes, or pipes.
Swaging is a forging process in which the dimensions of an item are altered using dies into which the item is forced. Swaging is usually a cold working process, but also may be hot worked.
A hose clamp (hose clip,hose lock or Jubilee Clip (UK)) is a device used to attach and seal a hose onto a fitting such as a barb or nipple.
Cross-linked polyethylene, commonly abbreviated PEX, XPE or XLPE, is a form of polyethylene with cross-links. It is used predominantly in building services pipework systems, hydronic radiant heating and cooling systems, domestic water piping, insulation for high tension electrical cables, and baby play mats. It is also used for natural gas and offshore oil applications, chemical transportation, and transportation of sewage and slurries. PEX is an alternative to polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC) or copper tubing for use as residential water pipes.
A hose coupling is a connector on the end of a hose to connect it with another hose or with a tap or a hose appliance, such as an irrigation sprinkler. It is usually made of steel, brass, stainless steel, aluminium or plastic.
Flare fittings are a type of compression fitting used with metal tubing, usually soft steel, ductile (soft) copper and aluminum, though other materials are also used. In a flare fitting the tube itself is "flared" i.e. expanded and deformed at the end. The flare is then pressed against the fitting it connects to and is secured by a close-fitting nut that ensures that no leakage happens. Tube flaring is a type of forging operation, and is usually a cold working procedure. During assembly, a flare nut is used to secure the flared tubing's tapered end to the also tapered fitting, producing a pressure-resistant, leak-tight seal. Flared connections offer a high degree of long-term reliability and for this reason are often used in mission-critical and inaccessible locations.
A pipe is a tubular section or hollow cylinder, usually but not necessarily of circular cross-section, used mainly to convey substances which can flow — liquids and gases (fluids), slurries, powders and masses of small solids. It can also be used for structural applications; hollow pipe is far stiffer per unit weight than solid members.
British Standard Pipe (BSP) is a set of technical standards for screw threads that has been adopted internationally for interconnecting and sealing pipes and fittings by mating an external (male) thread with an internal (female) thread. It has been adopted as standard in plumbing and pipe fitting, except in North America, where NPT and related threads are used.
A threaded pipe is a pipe with screw-threaded ends for assembly.
Thread seal tape is a polytetrafluoroethylene (PTFE) film tape commonly used in plumbing for sealing pipe threads. The tape is sold cut to specific widths and wound on a spool, making it easy to wind around pipe threads. Thread seal tape lubricates, allowing for a deeper seating of the threads, and it helps prevent the threads from seizing when being unscrewed. The tape also works as a deformable filler and thread lubricant, helping to seal the joint without hardening or making it more difficult to tighten, and instead making it easier to tighten. It also protects the threads of both pieces from direct contact with each other and physical wear and helps seal and prevent leaks from the connection.
An o-ring boss seal is a technique for joining two fluid-carrying pipes, hoses, or tubing. In an o-ring boss system, a male-threaded part is inserted into a female-threaded part, providing a mechanical seal. This system differs from others in that a nut is tightened over an o-ring in a chamfered area, creating a fluid-tight seal.
A fitting or adapter is used in pipe systems to connect sections of pipe or tube, adapt to different sizes or shapes, and for other purposes such as regulating fluid flow. These fittings are used in plumbing to manipulate the conveyance of fluids such as water for potatory, irrigational, sanitary, and refrigerative purposes, gas, petroleum, liquid waste, or any other liquid or gaseous substances required in domestic or commercial environments, within a system of pipes or tubes, connected by various methods, as dictated by the material of which these are made, the material being conveyed, and the particular environmental context in which they will be used, such as soldering, mortaring, caulking, Plastic welding, welding, friction fittings, threaded fittings, and compression fittings.
Pipe dope is any thread lubricant, thread sealing compound, or anaerobic chemical sealant that is used to make a pipe thread joint leakproof and pressure tight. It is also referred to as "thread compound" or "pipe thread sealant." Although common pipe threads are tapered and therefore will achieve an interference fit during proper assembly, machining and finishing variances usually result in a fit that does not result in 100 percent contact between the mating components. The application of pipe dope prior to assembly will fill the minute voids between the threads, thus making the joint pressure tight. Pipe dope also acts as a lubricant and helps prevent seizing of the mating parts, which can later cause difficulty during disassembly.
JIC fittings, defined by the SAE J514 and MIL-DTL-18866 standards, are a type of flare fitting machined with a 37-degree flare seating surface. JIC fittings are widely used in fuel delivery and fluid power applications, especially where high pressure is involved. The SAE J514 standard replaces the MS16142 US military specification, although some tooling is still listed under MS16142. JIC fittings are dimensionally identical to AN (Army-Navy) fittings, but are produced to less exacting tolerances and are generally less costly. SAE 45-degree flare fittings are similar in appearance, but are not interchangeable, though dash sizes 2, 3, 4, 5, 8, and 10 share the same thread size. Some couplings may have dual machined seats for both 37-degree and 45-degree flare seats. Komatsu and JIS fittings have flare ends similar to JIC fittings. Komatsu and JIS both use a 30-degree flare seating surface. The only difference is Komatsu uses millimeter thread sizes while JIS use a BSP thread. JIC fitting systems have three components that make a tubing assembly: fitting, flare nut, and sleeve. As with other flared connection systems, the seal is achieved through metal-to-metal contact between the finished surface of the fitting nose and the inside diameter of the flared tubing. The sleeve is used to evenly distribute the compressive forces of the flare nut to the flared end of the tube. Materials commonly used to fabricate JIC fittings include forged carbon steel, forged stainless steel, forged brass, machined brass, Monel and nickel-copper alloys.
Push-to-pull, push-to-connect, push-in, push-fit, or instant fittings are a type of easily removed compression fitting or quick connect fitting that allows an air line to be attached, nominally without the use of tools. These fittings act similar to the way regular compression fittings work, but use a resilient O-ring for sealing, and a grip ring to hold the tube in place.
Copper tubing is available in two basic types of tube—plumbing tube and air conditioning/refrigeration (ACR) tube, and in both drawn (hard) and annealed (soft) tempers. Because of its high level of corrosion resistance, it is used for water distribution systems, oil fuel transfer lines, non-flammable medical-gas systems, and as a refrigerant line in HVAC systems. Copper tubing is joined using flare connection, compression connection, pressed connection, or solder.
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