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The most important thing plumbers can do to ensure the reliability and performance of their customers’ plumbing systems is to avoid common mistakes in system installation. Here are four issues to watch for when installing non-metallic plumbing systems such as PEX and CPVC.
Probably the biggest opportunity to reduce failures that can be traced to installation is to ensure that all fittings in a system are installed properly.
With CPVC, the key factor is solvent welding all fittings. CPVC manufacturers strongly recommend against dry fitting a system as this increases the likelihood that the installer will miss a fitting or forget to go back and weld all the fittings. Instead, check the fit of each fitting immediately before solvent welding them. When this simple process is performed properly, the pipe and fitting are fused into a single piece of plastic that creates a joint that is stronger than the pipe or fitting on their own.
It’s also important to conduct quality inspections to check that each joint has been welded. New high-contrast green solvent cement for CPVC has been approved by all major code bodies for inclusion in their 2024 codes to make visual inspection much easier. High-contrast solvent cement, which is available for use today, follows the same installation instructions and provides the same bonding strength as the traditional, yellow-colored cement that could be difficult to see in jobsite lighting conditions.
With PEX, failures at fittings can occur due to improper crimping or expanding the fitting ring. With a PEX crimp fitting, too little pressure can result in a fitting that isn’t sealed and too much can cause damage. The key is ensuring your crimping tool remains properly calibrated. Tool calibration is similarly important with expansion fittings to ensure a proper fit without damaging the pipe or expansion ring. Proper installation practice is also important. While instructions differ between manufacturers, it is frequently recommended that expansion tools be rotated during expansion to avoid damaging the system, while crimp systems typically advise against “double-crimping” which may interrupt the seal from a crimp ring.
Another issue to watch for with the insert fittings is proper seating of the fitting and the ring relative to the pipe. PEX manufacturers have fairly strict tolerances regarding the positioning of the fitting, ring and pipe and failing to properly seat fittings or rings can lead to leaks. In some cases, these tolerances can be as small as 1/16th of an inch.
Expansion and Contraction
One of the strengths of CPVC is that its temperature and pressure ratings are unaffected by chlorinated water. FlowGuard Gold CPVC, for example, is pressure rated to 100 psi at 180 degrees and 400 psi at room temperature. However, expansion and contraction of the pipe caused by differences between the installation and operating temperature of the system and changes in the temperature of the water flowing through the pipe can easily exceed this limit if the pipe is restricted. The force of thermal expansion on a pipe that is restricted can exceed 1,200 psi under the right circumstances.
FlowGuard Gold CPVC will expand about 1 inch per 50 feet of straight length of pipe per 50 degree temperature increase. In many cases, expansion and contraction can be accounted for through normal changes of direction but be sure the natural movement of the pipe is not restricted and leave adequate spacing between elbows and hangers. Also avoid overtightening pipe hangers to the point where they can restrict lateral movement of the pipe. For long, straight runs, loops or offsets should be used. For underslab installations, install the pipe so that it snakes from side to side in the trench. If you have any questions, consult the manufacturer’s installation guidelines.
PEX systems will experience approximately 2.8 times more thermal expansion or contraction than a CPVC system. Because PEX is naturally very flexible, the effect of expansion can typically be accommodated by snaking or looping the pipe; however, when installing the pipe in hot conditions where the service temperature will be lower, plumbers should be careful to leave additional pipe to account for the thermal contraction that will occur when the pipe cools. Additionally, when looping PEX piping to accommodate thermal expansion, be careful to ensure that the movement of the pipe will not bend the loop beyond the published bend radius provided by the manufacturer.
All plumbing materials can be weakened by exposure to certain chemicals, and different plumbing systems are incompatible with different chemicals. For example, non-metallic plumbing systems may be incompatible with some household chemicals commonly stored under sinks. Copper stub-outs are generally recommended for these locations. As with all accessories, be sure to use stub-outs from manufacturer-authorized partners.
CPVC can be softened by the plasticizers contained in some rubbers and flexible vinyl products, so these materials should be prevented from contacting the pipe or fitting. You can use the FBC System Compatible Program to identify materials that are compatible and incompatible with FlowGuard Gold CPVC.
PEX is known to have compatibility concerns with closed-cell insulation, organic chemicals, strong acids, strong bases, solvents, petroleum distillates and adhesive tapes. The plastic fittings used in PEX systems are particularly vulnerable to damage from exposure to acetone, which is found in PVC primer and can cause the fittings to split or shatter under minimal stress. PEX can also be subject to permeation in which chemicals pass through the pipe and enter the water supply so avoid installing PEX where it may be exposed to chemicals such as pesticides.
One more issue that loosely fits within the category of material compatibility is UV exposure. CPVC and PEX have different reactions to UV light. CPVC will show signs of exposure in the form of discoloration, but UV light does not affect a CPVC pipe’s pressure-bearing capability or expected life.
With PEX, UV light consumes the chlorine-inhibiting antioxidants that protect the pipe from chlorine-induced oxidation, leaving the pipe more vulnerable to premature degradation. PEX pipes should be protected from UV exposure before, during and after installation as just one month of exposure can result in a 21% reduction in life expectancy depending on the cell class of the piping.
PEX also has compatibility issues with the disinfectants used in common water treatment processes as documented in the Plastic Piping Institute’s Technical Note 53. This note lists conditions that can accelerate the time to failure in PEX piping exposed to chlorinated water. These include temperatures above 140 degrees, pressures above 80 psi, and an oxidative reduction potential (ORP) level in the water flowing through the pipes above 825 mV.
The first two can be managed through various design practices that prevent pressures and temperatures from exceeding these limits or by avoiding PEX in applications where this isn’t possible, such as a gravity distribution system in a multi-story building where higher pressures may contribute to system performance. But the third is outside the engineer’s and plumber’s control.
ORP is an important parameter in assessing water quality and the effectiveness of water treatment processes. Chlorine is a significant contributor to ORP, but other factors also play a role, including the water’s PH level and the presence of dissolved oxygen and metal ions. Municipalities can change their treatment practices at any time, and a growing number have introduced chlorine dioxide into their water supply, which has a higher ORP than chlorine. This, combined with factors such as expanding distribution networks in which water has to travel farther to its destination, has resulted in ORP levels above 825 mV becoming more common. Even if the water in a particular home is below the threshold at the time of installation, there is no guarantee it will remain there.
The key with any plumbing system is to follow manufacturer-recommended installation guidelines as these have been developed to account for the specific characteristics of the manufacturer’s material. Plumbing system manufacturers also generally offer resources on their websites, such as tutorials and field guides, to assist plumbers new to a material or to serve as a refresher for those with experience. Making use of these resources can ensure you are always incorporating the latest best practices into each installation and avoiding mistakes that can compromise system reliability. For more information on CPVC plumbing systems, visit flowguardgold.com/plumber-resources.
Jonathan Simon is the North American residential plumbing manager for Lubrizol Advanced Materials Inc., the parent company for FlowGuard Gold Pipe and Fittings.