Can You Use Compression Fittings on PEX

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The increasing popularity of PEX pipes amongst DIY homeowners stems from its flexibility. You can easily bend it around structures, which usually require no connectors. 

However, extensive PEX piping systems will require installing connectors/ fittings for efficiency.

Compression fittings are the most convenient connectors you can use on PEX when dealing with multiple connection points. They are easy to install and disassemble, and you can easily connect them to metal and plastic tubing.

Despite their flexibility, the fittings create airtight seals across the piping system.

In this article, we will talk in-depth about compression fittings to enable you to determine which fittings you can use for your PEX piping.

Compression Fitting

Can You Use Compression Fittings On PEX

Before choosing the right compression fittings to use on PEX, you must first understand what these fittings are all about. A compression fitting enables you to connect PEX pipes or connect the PEX to a fixture, such as a water pump outlet.

A compression fitting comprises three parts; a compression nut, a compression ring, and a compression seat. The ring is also called a ferrule or a compression sleeve. The nut tightens the PEX onto the ferrule, creating a line seal between them. 

Since the PEX fits around the fitting, it reduces the internal diameter slightly. This is why it is crucial to expand the PEX before inserting the fitting. It helps minimize friction and maximize the flow volume of the entire piping system.

Compression fittings work both in high/low temperatures and pressures. Whether in freezing winter conditions or when connected to hot water systems, these fittings will work seamlessly without any leaks. 

How To Install Compression Fitting On PEX

Ease of connection is among the biggest advantage of using compression fitting on PEX. You can assemble, disassemble and reassemble a PEX connection in minutes. 

How you install these fittings primarily depends on the manufacturer’s design and specifications. While the installation manuals may differ, some procedures are usually the same. 

Across the board, you can install a compression fitting on a PEX pipe using these five easy steps:

  1. Cut the PEX pipe vertically and precisely using a pipe cutter and ream it
  2. Slid the compression nut and the ferrule over the PEX 
  3. Utilizing an expansion tool, expand the PEX to fit one end of the fitting
  4. Insert the fitting into the PEX up to the shoulders of the fitting 
  5. Using a clamp, fasten the compression nut until the ferrule aligns with the shoulders of the fitting. 

As you tighten the compression nut, it firmly latches the ferrules onto the PEX, creating an airtight seal. Tighter is not always better; overtightening the nut usually deforms the ferrule. Consequently, it weakens the seal, and you might experience leaks in your piping system. 

Disassembly of the fitting requires you to loosen the nut to replace or reassemble the PEX tubing. Reassembling follows the same procedure as the assembly. 

However, since the PEX swags slightly from the initial installation, you will have to tighten the nut a little more.

Apart from creating a tighter seal, retightening your compression nuts helps to break up corrosion on the threads. Retightening should be done only twice or thrice to avoid friction between the ring and the nut. Friction will eat away these parts, and you will replace them or the fitting body entirely.

If you’re looking for a video guide to install it rightly, you should watch this YouTube video below:

What Fittings Work With PEX

While compression fittings may look similar, they have some minute structural differences. For a fitting to work perfectly, you need to consider the following;

  1. The size of the PEX pipe 
  2. The threads
  3. The material

Let us expound on each consideration.

The size of the PEX pipe

The size of the PEX pipes determines the size and type of fitting you may use. If the fittings are bigger or smaller than the pipe, it is most likely to fail and create leakage problems. 

Luckily, most PEX manufacturers inscribe the pipe’s dimensional specifications on its surface. It is important to note that the size of PEX tubing is denoted by copper tubing size (CTS). 

Using the CTS of the PEX, you can acquire the corresponding compression fitting since the outside diameter of all pipes of the size is the same. 

The Threads

The threads can either be male or female. A male fitting has the threads on the outside, whereas the female has them internally. 

Before connecting the fitting, ensure the male and female threads have the same pitch and thread design.

The pitch is the distance, in millimeters, from the crest of one thread to another. On the design, you can have the parallel fitting, which has a uniform diameter, or a tapered thread whose diameter decreases from one end to the other. 

Tightening fittings with different threads per inch (TPI) can easily strip the threads or crack the compression fitting.

The Material

The durability of your fittings hinges on the quality and composition of the materials. Compression fittings you can use on PEX are primarily made of copper and brass.

You can use copper compression fittings on PEX since it’s more flexible and has better thermal conductivity than brass. It is easily malleable and light but strong, with the fittings available in various sizes and designs. 

Despite oxidation over time which can clog the PEX pipes, these fittings are reliable and durable. The metal will form a green patina to protect itself from further oxidation.

A brass fitting, an alloy of copper and zinc, presents a cheaper alternative to copper. However, brass is not only structurally sound, but it is aesthetically pleasing. Most of the fittings have plated finishes that look great but offer more corrosive resistance. 

You must also check if the brass fittings are for metals or plastic. Brass sleeves for metal pipes are known to sear through PEX and other plastic pipes. Gradually, the fluid pressure will cause leaks.

It would be best if you avoid mixing and matching components from two different manufacturers. Incompatibility may bring about improper tightening and damage to the threads resulting in leaks. 

Moreover, it makes the piping system susceptible to high-pressure busting, leading to expensive pipe repairs and installations.

Final Words

You can use compression fittings on PEX even under harsh operating temperatures and pressures. While you might require a few tools, the installation is relatively simple and easy. Nonetheless, remember to read and abide by the specific assembly recommendations of the compression fitting.

We hope this guide will help you identify if you can use compression fittings on PEX. Besides, it will help you pick out the best compression fitting across a number of different products available in the market.

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