Compression fittings use a nut and ferrule or O-ring to create a seal in plumbing applications. They are easily installed and can be reused by replacing the ferrule or O-ring. They are not as durable as welded connections but are preferred for occasional removal or disassembly.
Compression fittings use a nut slipped over a length of tubing followed by a ferrule or O-ring. This nut is tightened against another line or fitting, which in turn compresses the ferrule or O-ring, thus creating a seal. Compression fittings are most commonly found in plumbing applications where quick and easy sealing is required. Fittings are typically a disposable product, but many types of compression fittings can be reused by replacing the ferrule or O-ring and re-tightening the nut.
Found under many home and commercial sinks, compression fittings provide watertight seals in drains, as well as water lines and faucet fixtures or fittings. Fittings rarely require more than hand tightening to achieve a seal and can also be used when mixing plumbing types such as stainless steel with copper or plastic. Compression fittings rarely require pipe sealant or Teflon thread tape to achieve a tight seal. On rare occasions, a fitting will require a slight twist with a wrench to complete the seal.
Often used in confined spaces that would make welding a fire hazard, compression fittings are easily installed. These fittings are also used in high risk applications such as oil and gas lines where the application of flame or heat would be too dangerous. The most common cause of compression fitting failure is overtightening during installation. Overtightening the ferrule becomes out of round and fails to provide a complete seal. When the fitting is sealed, a leak test is performed. If there is a leak in the fitting, the nut is slowly tightened until the leak disappears.
While extremely useful for sealing plumbing lines, compression fittings aren’t as durable or as visually impressive as sweaty, welded connections. In applications subject to overtightening or rigorous use such as an outdoor water faucet, a welded connection may be a better option than compression fittings. Additionally, in areas and applications prone to vibration and waterline vibration, the welded connection may prove to be more durable.
In applications that require occasional removal or disassembly for meter maintenance or replacement, compression fittings are preferred for ease of reassembly. Requiring little or no tools to complete assembly, the compression fitting is easy to install in an emergency and is often installed as a temporary fix to a problem that will eventually be resolved by applying a welded connection.
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