The Potential Leak in Your Kitchen Cabinet – Flexible Supply Connectors

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One of the more innovative products to emerge on the plumbing scene in the past 20 years or so (in my opinion) is the flexible supply connector.  A lot of people have seen but probably not paid much attention to them under their sink or perhaps from the toilet supply valve to the toilet tank.  Most have a stainless steel braided exterior that covers a flexible tubing inside, although some models only have the flexible tubing without a braided covering.

Flexible water supply line

These flexible supply connectors speed up the installation process compared with the soft copper, chrome plated supply lines you may have seen in an older home. The flexible connector’s “flexibility” allows you to compensate for misalignment of the supply stop valve and the plumbing fixture with more forgiveness than a soft copper supply line.  The flexible connector is often easier to work with than an old school copper supply line because the flexible connector can be formed and routed more readily than the copper product.  The small diameter of the copper supply line often allows it to collapse and crimp, impeding flow and usually ruining the copper supply line.

However, for all the pluses of the flexible connector, there are some limitations.  This figure below shows one of the common defects in the installation of a flexible plumbing connector, overtightening the plastic fitting.  Note the crack around the perimeter of the plastic fitting on the braided supply connector.  Installers can at times overtighten a fitting and the result is a failed connector and water damage to the home or business. The copper supply line used a compression ferrule type connection where tightness is key to preventing leaks in contrast to the flexible connector.

Cracked connector

While flexible connectors are great for allowing offsets and avoiding interferences, they do not hold up well when “stretched” because the flexible supply connector is too short for the application.  It is a much better installation practice for the flexible supply line to be a little longer than needed.  Installing a flexible supply that is “stretched” to fit can cause the line to fail where the flexible tube joins the metal connector, resulting in a leak.

Another form of failure that I have seen is chemical attack of the braided stainless steel exterior of the flexible supply line.  See the broken, corroded strands in the photograph below. With the stainless steel braids broken, the flexible tubing beneath lacks support and often bulges out, allowing the tubing to fail as noted.

Corroded supply line

Stainless steel is more resistant to most types of corrosion than plain carbon steel. However, note that the name is “stainless” not “stainproof” and stainless steel will corrode.  Stainless steel comes in different grades, with 300 series stainless being more resistant to most corrosion than 400 series stainless steel.  Many people store cleaning chemicals in the cabinet under their kitchen sink.  Depending on the chemicals stored, an unsuspecting homeowner could be subjecting their braided stainless steel supply lines to chemical attack, resulting in a premature failure.  Some manufacturers coat their braided stainless connectors to resist corrosion, however budget items could be uncoated and may fail prematurely if exposed to chemicals.

A report published in 2017 by the largest insurer in Australia, IAG, noted that their claims data indicated that 22% of the water damage claims in 2016 were attributed to flexible hoses.  I have not found similar data from American insurers, but it is reasonable to draw parallels between Australia and the United States with regards to this information.

While flexible braided stainless steel supply lines offer many advantages to a soft copper supply line, they are not without their limitations.  An installer should be familiar with proper installation techniques and follow them.   Property owners should be aware of their limitations as well when performing do-it-yourself plumbing jobs.  Proper application and installation of flexible plumbing connectors are critical to the life of the product.

Chad Jones, PE, CFEI, CVFI, CMSE has a Bachelor of Science in Mechanical Engineering from Clemson University. Chad has over 25 years of engineering experience including mechanical, process, and manufacturing engineering. This work has included equipment design, machine safeguarding, cost estimating and safety compliance. Chad also has over 10 years of commercial, industrial, and residential HVAC and plumbing design experience. A lifelong auto and motorcycle enthusiast, Chad is accomplished in the maintenance, repair, and modification of vehicles and engines. Chad is a Certified Fire and Explosion Investigator, Certified Vehicle Fire Investigator, and IFSAC certified Firefighter II in Greenwood County, South Carolina.

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