Making a Connection: A Comprehensive Guide to Putting Together PEX Pipe

Compared to rigid pipe, flexible PEX pipe has a lot of benefits in areas such as durability, reliability and cost-effectiveness. But when it comes to system installations, what connection method is best?

The five most common connection methods for PEX piping systems are crimp, clamp, push-to-connect, expansion, and expansion with compression. Here’s a more detailed look at each connection style and their benefits and challenges.

Crimp

The crimp connection method uses a copper ring on the outside of the pipe and an insert fitting that goes into the pipe. It is governed by the following ASTM standard specifications: F1807 for metal insert fittings and F2159 for plastic insert fittings.

To make a connection, start with a clean, straight cut on the end of the pipe. Then, slide the crimp ring over the end of the pipe and insert a fitting into the pipe. Slide the ring back toward the end of the pipe where the pipe and fitting overlap. The ring’s location varies based on manufacturer, so always refer to the manufacturer’s instructions.

After positioning the ring in the proper location on the pipe, place the head of a crimp tool around the ring and compress the ring until the tool stops. After making the connection, be sure to use a go/no-go gauge to verify a proper connection. Loose crimps can result in leaks, and crimps that are too tight can damage the pipe or fitting.

If done properly, crimp connections are an easy-to-learn, fast-to-install, inexpensive method for connecting PEX. Tools and rings are readily available at most retailers. Just remember to purchase separate tool heads for each pipe size.

These connections are approved for installation behind walls and direct burial in soil. However, when burying in soil, the copper crimp ring can be susceptible to corrosion, so it’s important to wrap the connection with an impermeable material.

The main drawback with crimp fittings is that they actually work against the properties of PEX. How? PEX pipe features “shape memory,” which means the pipe always wants to return to its natural shape. When the pipe is crimped down, it always wants to push back against the crimp ring — and away from the fitting — to return to its natural shape. Over time, this can lead to potential leaks if the installer is not using a go/no-go gauge and the crimp is a bit loose.

Another downside with using insert fittings is the smaller internal diameter compared to the pipe. This can restrict flow and decrease system performance. Also, being able to insert the fitting without formally making the connection can also increase the instance of dry fits.

Clamp

The clamp connection method uses a stainless-steel ring on the outside of the pipe with an insert fitting going into the pipe. This method adheres to the ASTM F2098 standard specification.

To make a proper connection, the installer must first ensure the tool is properly calibrated. Then, the process is similar to a crimp connection: Start with a clean, straight cut on the end of the pipe, slide the ring over the pipe, insert the fitting and position the ring back over the pipe and fitting (again, the position depends on the manufacturer). After properly positioning the ring, use a clamp tool to compress the ring until the tool stops. Most tools won’t release until the connection is complete.

Like crimp connections, clamp connections are fast and easy to learn, quick to install and the products are readily available at a variety of retailers. However, clamp connections offer a slight advantage as they only require one tool for any size connection. There’s no need to purchase separate heads for different pipe sizes. Also, the clamp connection is easier to disassemble than a crimp connection if the connection needs to be removed.

The downside is that, just like the crimp method, it goes against the properties of PEX. As time goes on, the pipe will continue to resist the strength of the ring around it. Because fittings with a smaller internal diameter are inserted into the pipe, it creates restriction to water flow.

Like PEX crimp connections, the PEX clamp connection is approved for installation behind walls and direct burial in soil. And while the stainless-steel rings are not corrosion-resistant, they have the potential to provide slightly more resistance to corrosion compared to copper crimp rings.

Another important note: Calibrating the tool is important. A miscalibrated tool will result in leaks or damaged fittings. Manufacturers’ recommendations vary on how often to calibrate the tool, so be sure to follow the proper calibration frequency.

Push-to-connect

The push-to-connect fitting method, which conforms to the ASSE 1061 standard specification, uses a fitting and, depending on the manufacturer, an insert stiffener. To make a connection, the installer inserts a stiffening sleeve into the pipe (based on certain manufacturers’ instructions) and then pushes the pipe into the fitting. 

When done properly, this is a quick, easy method for connecting PEX. No special tools are needed and the fittings can be removed and reused easily. However, since this method is relatively new to the PEX market, its availability may be limited compared to other products.

Also, due to its higher cost, some in the industry consider push-to-connect a “temporary fix” fitting. Contractors will keep a limited stock on hand for emergencies but then go back and make a “permanent” connection with a different connection method and keep the push-to-connect fitting for another fast fix later.

While push-to-connect fittings are approved for installation behind walls as well as direct burial in soil, the fittings must first be wrapped in an impermeable material to protect the connection from ground contaminants.

Lastly, because some fittings require an insert stiffener and some don’t, it can be difficult to ensure a proper connection is made. The stiffener sleeve keeps the pipe rigid on the inside to make a good seal against the fitting O-ring. If the installer doesn’t push the fitting on far enough and misses the sleeve, there can be potential for leaks. Also, because PEX is more malleable than metal, the fitting’s teeth have the potential to slide off the pipe when subjected to increased pressure or freezing conditions.

Expansion

PEX expansion (also known as cold expansion) conforms to the ASTM F1960 standard specification and uses a PEX expansion ring and a fitting with a larger internal diameter to make a connection.

Just like with all PEX connections, the process starts with a clean, straight cut on the end of the pipe. Then, a PEX expansion ring slides over the end of the pipe. Most rings feature a stop edge to ensure the ring has a 1/16-inch overlap on the end of the pipe. For rings without a stop edge, leave a 1/16-inch overlap before making the connection.

Insert the cone of the expansion tool into the end of the pipe and (with automatic expansion tools) press the trigger to begin expanding the pipe and ring. With manual tools, you must “pump” the handle of the tool to make an expansion.

The required number of expansions can vary by pipe size, but a typical rule of thumb is to expand the pipe until it reaches the head of the tool and then do one more expansion.

Once the pipe and ring are properly expanded, remove the tool and insert the fitting. Be sure the fitting goes all the way into the pipe so the shoulder of the fitting meets the end of the pipe and ring. As the pipe and ring shrink back down to their original size, it creates a strong connection that will continue to press onto the fitting and continue to get stronger over time. Remember the “shape memory” of PEX? Here’s where that advantage comes into play.

This connection system is easy to learn, fast and easy to install, and impossible to dry fit (because the fitting internal diameter is larger than the pipe). Plus, it offers the greatest flow and system performance. Additionally, it eliminates the need for go/no-go gauges as well as tool calibration. If the end of the pipe and ring are touching the shoulder of the fitting, the connection is good.

Since this product is considered more “professional grade,” products and tools are only available through professional plumbing supply distributors to trained installers. Additionally, the tool requires different head sizes for each pipe size, so it’s important to purchase the proper head sizes for each pipe size you plan to install.

Tools are available in “manual” and “automatic” versions. Automatic tools feature auto rotation, which rotates the head with each expansion. This ensures no deep grooves on the interior of the pipe which can lead to leak paths. If using a manual tool, you must manually rotate the tool after each expansion.

The expansion method is approved for installation behind walls, in soil and also in concrete. This is the only PEX fitting system that can be buried in concrete.

A couple important factors to know when making expansion connections: Because the connection is so strong, if you have to remove a connection, you have to cut out the connection completely and start over with a clean cut of pipe and a new fitting. Also, when making connections in colder weather (below 40 degrees F), the connection time will take longer. Limit the number of expansions in cold weather and, if necessary, use a heat gun or hair dryer to warm the pipe and ring for a solid connection.

Expansion with compression

Following the ASTM F2080 standard specification, the expansion with compression method utilizes both an expansion process to insert a fitting and then follows with a compression sleeve pulled over the pipe and fitting to make the connection.

Again, the process starts with a straight, clean cut of pipe. Then, the metal compression sleeve slides onto the pipe far enough to leave room for inserting the fitting. The system uses a special tool featuring an expansion head on one end and compression jaws on the other. The installer makes one expansion, then rotates the pipe to make one more expansion before inserting the fitting. Then, the tool is turned around to use the compression jaws to compress the sleeve over the pipe and fitting.

The benefits of this connection method include immediate pressure testing, no issues with cold temperatures and better system flow due to the expansion of the pipe before inserting the fitting. 

Like with expansion products, the expansion with compression products are also sold through professional plumbing supply distributors. Also, the tool requires different sized heads as well as different sized compression jaws for each pipe size.

Because this connection method is a two-step process, some installers report it can take longer to make a connection, especially when both the heads and the jaws must be changed out for different pipe sizes (think: reducing tees).

Another challenge with this type of connection is the pinch point danger with the compression jaws when the tool is pulling the sleeve over the pipe and fitting. There is no safety mechanism to back the jaws off the sleeve if a finger gets in the way.

Lastly, some contractors have reported that the tool is hard to get into tight spaces to make the final compression step of the connection. This can prove challenging when you’ve made the expansion and inserted the fitting, but you can’t get the tool into the right location to finish the compression.

A last piece of advice

While understanding the benefits and challenges with each connection method is important for the best installation experience, there is one vitally important point to keep in mind when installing a PEX piping system.

Because most PEX manufacturers offer a warranty with their product (some up to 25 years), it’s important to stick with one brand. Why? Because once you start mixing brands for the pipe, fittings, sleeves and rings, that warranty may be greatly reduced or void.

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