Making the Connection With PEX: The Good, the Bad and the Ugly

A closer look at copper crimp, stainless steel clamp, push-to-connect and cold expansion with reinforcing rings.
Making the Connection With PEX: The Good, the Bad and the Ugly
To make an expansion connection, the installer expands the pipe and ring before inserting a larger ID fitting.

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Recently, I came across an online article that featured contractors’ experiences with various types of cross-linked polyethylene, or PEX, connection systems — crimp, clamp, push-to-connect and cold expansion. I was intrigued to learn how different contractors get the job done and how they regarded the different types of PEX connections available. It made me think about some questions other contractors might be contemplating when it comes to installing PEX piping systems, such as …

  1. Why use PEX?
  2. What do I want to achieve with my installations?
  3. Am I using the product correctly?

With more than a decade in the industry, I thought I’d take a stab at answering these three questions, while offering some information about PEX fittings.

My purpose is to generate greater awareness of the offerings available and to clear up any concerns or misinterpretations installers may have.

Why use PEX?

The answer is two-fold. First, copper is expensive (and costs can fluctuate drastically). So many plumbing and heating professionals have switched to PEX to stay competitive.

While this is probably the most common reason for switching, there are other reasons as well.

  • For one, PEX is flexible, so it can bend with each change in direction. This reduces the number of required connections, making installations faster and easier — and lessens the chance of potential leak points.
  • The flexibility of PEX also means it can expand and contract to its original size, making it highly resistant to damage from frozen water in the pipes. Certain types of PEX can even expand up to three times the pipe’s diameter.
  • PEX also resists corrosion, pitting and scale buildup, so there’s never a concern about pinhole leaks or restricted water flow.
  • ASTM International, a standards organization, requires that the life expectancy for PEX pipe be at least 50 years. (Some PEX manufacturers offer a pipe life expectancy of more than 100 years.) In short, PEX is more durable and provides longer system longevity with less time and material invested in the installation.

The bottom line: PEX is more durable than copper, and it lasts longer.

What do I want to achieve with my installations?

There can be a lot of answers to this one, but let’s hope customer satisfaction is at the top of the list. Along with that, faster installations — with fewer callbacks or rework — are probably also a priority.

For most installers, callbacks and rework are the worst. Nothing hurts the bottom line more. Imagine having an already small margin in order to win a project, only to have that margin eaten up by your first callback. You might not even have to imagine it; you may be routinely experiencing it.

That always leads to the next, and most important, question …

Am I using the product correctly?

To answer this, we’ll take a closer look at the four most common PEX connections:

  • Copper crimp
  • Stainless steel clamp
  • Push-to-connect
  • Cold expansion with PEX-reinforcing rings

Understand that all PEX has some degree of thermal elastic memory. This is important when comparing how the connections function over time.

Copper crimp rings fall under two standards: ASTM F1807 for metal insert fittings and ASTM F2159 for plastic insert fittings. The process for making a connection on a square-cut, clean pipe is as follows.

  1. Slide a crimp ring over the end of the PEX pipe.
  2. Insert a fitting, either metal or plastic, into the end of the pipe.
  3. Slide the ring into position over a point where the pipe and the fitting overlap. The distance from the edge of the pipe varies, based on material type and manufacturer.
  4. Using a crimp tool, compress the crimp ring until the tool stops.
  5. Use a go/no-go gauge to verify each connection has been made properly. These gauges vary by manufacturer, as do their operations, but the job of the gauge is consistent. Essentially, the installer is trying to determine whether or not the connection is too loose (resulting in the potential for leaks), or too tight (resulting in the possibility of damaged pipe or fittings, another potential leak point). The go/no-go gauge will also help determine if the crimp tool needs to be recalibrated.
  • The good: When connections are done properly, this should be a relatively fast and inexpensive way of connecting PEX. There are a variety of different tools and crimp-ring manufacturers. These parts are easy to purchase at a variety of retailers.
  • The bad: Not all tools work well in tight spaces. A majority of them are large, so the installer has better leverage on the crimp connection. Due to the nature of PEX pipe, the strongest this connection will be is when it’s initially made. As time goes on, the pipe will resist the strength of the crimp ring. Additionally, the fittings are inserted into the pipe and create a restriction to water flow. This can possibly result in having to upsize system piping.
  • The ugly: Manufacturers’ recommendations for making crimp connections vary, as do tools and warranties on the parts and pieces. There is no way to inspect the fitting visually; a special go/no-go gauge must be used. The go/no-go gauges also vary by manufacturer.

The scariest part about the go/no-go gauge is when there isn’t one. Many installers I’ve talked to don’t even own one. This inevitably leads to a higher occurrence of dry fits; i.e., a connection that was overlooked and never crimped. Another concern is that because these parts are relatively easy to purchase at a variety of retailers, it means any untrained individual can purchase and install these types of fittings.

Stainless steel clamp rings fall under the ASTM F2098 standard. The process for making a connection on a square-cut, clean pipe is as follows.

  1. Calibrate the crimp tool.
  2. Slide a clamp ring over the end of the PEX pipe.
  3. Insert a fitting, either metal or plastic, into the end of the pipe.
  4. Slide the ring into position over a point where the pipe and the fitting overlap. The distance from the edge of the pipe varies based on material type and manufacturer.
  5. Using a crimp tool, compress the crimp ring until the tool stops. Most tools will not release until the connection is complete.
  • The good: When connections are done properly, this should be a relatively fast and inexpensive way of connecting PEX. There are a variety of different tools and crimp-ring manufacturers, and these products are relatively easy to purchase at a variety of retailers. The tools are generally one size fits all, so a 1/2-inch connection and a 1-inch connection can be made with no adjustment to the tool.
  • The bad: Just like the crimp method, not all tools work well in tight spaces. Once again, this connection will be at its strongest when it’s initially made. As time passes, the pipe will resist the strength of the crimp ring. Again, like copper crimp fittings, stainless steel clamp fittings are inserted into the pipe and therefore create a restriction to water flow.
  • The ugly: The manufacturers’ frequency recommendations for calibrating the tools vary: from “every day” to “once in 30,000 connections.” A miscalibrated tool will result in leaks or damaged fittings, but the installer or building owner won’t know that until it’s too late. Also, the clamp rings can be susceptible to corrosion. If they fail at any point, there will be a catastrophic failure.

Push-to-connect fittings conform to the ASSE 1067 standard. The process for making a connection on a square-cut, clean pipe is as follows.

  1. Depending on the fitting, insert a stiffening sleeve into the PEX pipe.
  2. Push the pipe into the fitting per the manufacturer’s instructions.
  3. Follow any additional manufacturer’s instructions.
  • The good: When connections are done properly this should be a quick way to install a PEX system. Push-to-connect can be used interchangeable with most types of copper tube size pipe, including PEX, copper and CPVC. No special tools are needed to make these connections. Also, the fittings can be easily removed and reused.
  • The bad: If cost drives your decision, steer clear of push-to-connect. Most contractors with whom I have spoken will have a variety on hand for emergencies, but don’t generally stock a large number. Many installers will use them as a temporary fix, and then reuse them again for the same reason — as a stopgap. If a sleeve is required, there will be a restriction to water flow.
  • The ugly: Some fittings require a stiffener sleeve and some don’t. The job of the sleeve is to keep the PEX rigid on the inside to make a good seal against the O-ring inside the fitting. You can’t visually see whether or not a stiffener was installed or whether the pipe was pushed into the fitting enough to create a proper seal. If you miss the sleeve or don’t push hard enough, you’re going to get leaks.

In addition, when the PEX pipe is put under pull stresses, connections can more easily fail. The issue is not fitting strength. Rather, the PEX material is soft enough that the teeth inside the fitting will scrape away the pipe until it slides off completely.

Cold expansion with PEX-reinforcing rings fall under the ASTM F1960 standard. The process for making a connection on a square-cut, clean pipe is as follows.

  1. Slide the PEX-reinforcing ring over the end of the pipe. Most rings have a stop on the end of it. If not, leave a small space at the end of the ring before starting the connection.
  2. Using an expansion tool, expand the pipe per the manufacturer’s instructions. Do this until the pipe is expanded wide enough to receive an F1960 fitting.
  3. Insert the fitting into the pipe until the shoulder of the expansion ring touches the shoulder of the fitting.
  • The good: Unlike other types of connections that require tool calibration or go/no-go gauges, this is a completely visual connection. If you can see the expansion ring touching the shoulder of the fitting, it is connected properly. The properties of PEX work with this connection. Due to the shape memory of PEX, the weakest that this connection will ever be is when it is first joined. As the PEX contracts, it will increase the strength of the connection.

The fittings have virtually the same inside diameter as the pipe, creating less restriction and often allowing for smaller pipe sizes. It also makes the connection impossible to dry-fit. The tools are close to one size fits all, with the exception of the expansion heads, which need to be changed out for different pipe sizes.

  • The bad: If the expansion tool does not have autorotation built in, there is an extra step of manually rotating the tool between expansions. If the expansion tool is equipped with autorotation, the tool must be visually inspected to ensure functionality. (I recommend daily inspection.) Also, the fittings are not easily found in big-box retail stores; they are generally only sold to trained, professional plumbing and HVAC installers.
  • The ugly: If you don’t have autorotation and you don’t manually rotate the tool, you might get leaks. Without rotation, small grooves could form on the inside wall of the pipe and create a small leak point. Temperatures also affect the number of expansions needed for a fitting. In cold conditions, you need to be careful to not over-expand the pipe, because over-expanded pipe takes longer to contract in cold conditions. However, a heat gun or hair dryer will fix leaks caused by over-expansion in cold conditions.

These are the four main methods for joining PEX piping systems. Learning the pros and cons of each will help you determine which connections will be more reliable for your project.

About the author: Dan Hubbard is the customer trainer at Uponor Academy in Apple Valley, Minnesota. He can be reached at dan.hubbard@uponor.com.



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