Known for their versatility, compression tube fittings can be found in a variety of applications that require connections between metal and hard plastic tubing. Their ability to handle temperature and pressure extremes, along with their relatively easy assembly and long lifespan, make compression fittings a common choice for situations where leaking pipes are simply not an option—from medical devices to large-scale gas lines.
Compression tube fittings are typically made from brass or copper, but there are also stainless steel and heavy plastic models available. The design of compression fittings consists of:
- A compression nut or screw
- One or more metal or graphite rings or caps known as ferrules
- A compression fitting body
How They Work
When the tubing is inserted into the end of the fitting and the nut or screw is tightened, it pushes the ferrule into the body and compresses it around the pipe. This compression is what creates a tight seal.
While metal-to-metal seals are considered fundamentally prone to leaks due to the pressure build-up between tubing made from hard materials, compression fittings can effectively alleviate that concern.
Designed to provide an optimal seal against both the tubing and the fitting body, there are several factors that can dictate the ultimate reliability provided by compression tube fittings: from the shape of the ferrule ring and how it connects with the fitting body, to the number of ferrules contained in the design (one or two pieces), to the tubing that is being connected.
In general, compression fittings are not recommended with soft tubing such as PVC or vinyl because the walls can collapse due to the pressure that is generated.
Compression vs. Solder Fittings: Pros and Cons of Each
When copper pipes are connected by soldering, it uses a process also known as “sweating.” Sweat fittings feature a non-threaded joint and a diameter slightly larger than the adjoining pipe. When placed onto the pipe, the application of hot solder seeps into the gap and joins the fitting onto the pipe.
Sweat fittings are typically used to do things such as form angles and junctions between pipes and change the pipe diameter. While compression fittings can be utilized for those types of functions, their ability to handle high pressure makes them more commonly used for connecting valves and water supply lines. They can usually be found at the pipe’s end point.
Compression fittings can often be used at pressures in excess of 10,000 PSIG (pound-force per square inch) and can even become more leak-proof with higher pressures, which further expand the tube against the ferrule ring. Hence, you often see water supply lines—and all gas supply lines—with compression fitting ends.
Both compression and solder fittings are considered permanent. But for the non-professional plumber, the compression fitting can generally be disassembled and reassembled as needed. DIYers who aren’t proficient at working with soldering devices to heat and connect fittings may be less inclined to re-solder a mistake. And because water lines must be completely dry when soldering (any water will impede the warming of the pipe to the point it can melt the solder), working with sweat pipe fittings requires more planning time.
Quicker-connecting compression fittings are also often used in situations where the use of a heat source such as a soldering iron is not permitted or possible, such as near a gas line or in enclosed spaces.
However, compression fittings are certainly bulkier and less streamlined than soldered joints. Especially when dealing with exposed piping, a soldered fitting may be considered because it is more aesthetically pleasing.
Causes and Prevention of Leaks
When installed properly, compression fittings are generally secure against leaks. However, that does not mean that leaks can never occur.
For example, while generally considered more reliable than soldered fittings, compression fittings can lose their seal when subjected to constant vibrations. And compression fittings that are repeatedly bent can cause the ferrule ring to lose its grip on the tube. Additionally, they are prone to leaks if the pipe inserts are not installed completely straight.
The good news is, in many cases, leaks in compression fittings can be repaired by simply tightening the nut more firmly. In fact, many plumbing experts recommend not over-tightening a compression fitting and instead leaving at least one additional thread in case of a potential leak down the road.
In general, copper compression fittings can be reused as long as they haven’t been tightened and re-tightened several times. Simply clean both mating faces and stay away from tape or plumber’s putty, which can compromise the threading. In contrast, many experts don’t recommend re-using the ferrule rings themselves after they have been compressed.
The final decision
Consider the pros and cons of compression tubing before deciding if it is the right choice for your job. But if you are looking for a quick fix that can handle high pressure and stay reliably leak-free, compression fittings are usually the preferred method over soldered fittings.
Product Compliance and Suitability
The product statements contained in this guide are intended for general informational purposes only. Such product statements do not constitute a product recommendation or representation as to the appropriateness, accuracy, completeness, correctness or currentness of the information provided. Information provided in this guide does not replace the use by you of any manufacturer instructions, technical product manual, or other professional resource or adviser available to you. Always read, understand and follow all manufacturer instructions.