There are various ways compression fittings are used. Compression fittings are required in both plumbing and electrical conduit systems to join pipework or tubing together. They are also used in toilet stop valves and hot and cold water taps in domestic and industrial settings. As well as being used in the construction industry, compression couplings are common in oil and gas, biotech, and chemical industries.
What is a compression fitting?
Generally, a compression fitting consists of an inner ring and outer nut, made either of brass and copper. The inner ring is known as a ferrule. This fitted over pipes to be joined and the outer nut slipped over it. The piping is then clamped together by tightening the nut so it presses against the ring creating a tight fitting that should be air tight and water tight seal. When larger compression fittings are required, there is usually a flange, rather than a single nut, with a ring of bolts each of which must be tightened evenly to ensure a proper and effective seal. In all cases, the nut should not be too loose or over tightened as this can compromise the fitting and cause leakage.
Types of compression fitting
There are two different types of compression fittings - standard and flared. The standard compression fitting is used mainly in plumbing and compressed air applications. They are used to connect a pipe to a valve, unite pipes, make connections to pumps and filters and make connections to tank fittings.
Advantages of standard compression fittings
Though the simplest of compression couplings, the standard fitting does its job perfectly well. When all that is required is the joining of tow lengths of pipe, a standard compression fitting is totally suitable. There is no advantage in making the connection more complicated than it needs to be.
The biggest advantage standard couplings have over flared compressions is thanks to their simplicity and the requirement of one ring and one nut, fitting is straightforward and can be installed with the minimal of tools and fuss to achieve a satisfactory result. Most standard compression fittings can be completed with standard tools, such as a wrench to tighten the nut. They do not require soldering and can be completed by non-professionals. This also means that a standard fitting is much faster to complete than a flared fitting.
Another advantage is that when making a standard coupling, there is no need to alter pipework. When a flared fitting is required, the pipe/tube needs to be altered to match the flare of the fitting. This requires a special tool. The resulting flared joint offers a tighter, more reliable seal preferred in chemical and electrical piping and high-pressure systems such as oil and gas pipelines. As these industries have more and higher danger risks when a pipe leaks, they require the most robust fitting against dangerous and costly leaks.
On the issue of cost, standard compressions are the lowest priced option, requiring just the ring or nut and minimal labour. Another advantage is that the simplicity makes them as easy to disassemble as assemble.
Standard compression couplings vs soldered joints
Although not specifically a disadvantage because a well fitted coupling provides a reliable seal in the majority of cases, there are instances when a soldered joint provides greater durability and reliance. In conditions where a joint is prone to flexing, this can affect the integrity of a standard and/or flared compression joint; a soldered joint is preferable. A soldered joint is more difficult to install and takes longer, requiring specific tools.
It should be noted however, that soldered joints are not suitable where the heat required for installation poses a danger, such as a gas or oil pipe.
Standard compression couplings vs threaded joints
Threaded fittings (i.e. a screw-form type fitting) work well on malleable materials such as aluminium, copper, brass, iron and polymers and can provide a leak-tight joint. However, there is often a minute opening at the root of the thread. Trying to compensate for this can cause overtightening, reducing the integrity of the joint. Further tightening deforms the metal and increases the risks of leaks. Standard and flared compressions overcome the issue of metal deformation. Standard and flared compression couplings are also more suited to harder materials such as stainless steel than a threaded joint.
The point, like most things, is to choose the best joint for the job. Don’t overtighten and periodically check the integrity of the joints.
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