By Tom Raguz and Jackie DeThorne

Summary: To get the most out of your water treatment system, one must pay special heed to proper valve and tubing connections. By using an easy-to-remember acronym, you’ll save yourself a lot of trouble and expense down the road.

Let’s face it, many of us have done it ourselves. After spending a lot of time and energy, not to mention money, on certain elements of our water conditioning and purification systems, we shrug off the critical nature of the right connections. For the short-term, we may even save money; but we pay for it in long-term aggravation. A systems approach to conditioning and purification considers the entire flow path—from the water source to the end user—while maintaining integrity of both the pure product and the path it travels.

Water is a necessary part of life with which many of us have a love-hate relationship. We love its beauty, the life it supports (ours and those close to us), and the power it generates. We hate the damage it creates when systems leak, pipes burst or freeze, and when other containment or control methods fail. Thus, it’s critical that not only each individual element of the circuit be considered, but the way they connect one with another.

Put a STAMP on it
Selecting the right fitting or tubing can be challenging or it can be easy. Over the years, many helpful acronyms have developed in regards to this process, but none as powerful as STAMP:

  • Size,
  • Temperature,
  • Application,
  • Media, and
  • Pressure.

Considering these five elements before installation will greatly reduce the time needed when trying to decide what fitting or tubing is right for your system.

Typically, one can find both ¼-inch and 3/8-inch outer diameter (OD) tubing with under-the-sink reverse osmosis (RO) systems. The RO unit itself may be outfitted with ¼-inch tubing but the supply line is 3/8-inch. Installers often settle on using multiple fittings and valves to supply water to the RO unit, which only complicates matters. At least one manufacturer has come up with a solution—the water supply valve. This new valve is a push-to-connect tee with an integrated valve within the handle. This one fitting not only saves time and money but there is less of a potential for a leak due to the reduced number of fittings.

The next design question is temperature. It’s the primary reason some manufacturers offer fitting products in multiple materials.

Acetal has been used in the water treatment industry for years. Typically, acetal is used in cold water applications but can see intermittent warm water usage.

If your system temperature requirements are between 180-to-225°F, polypropylene is your answer.

For those applications requiring even higher temperatures, PVDF is the material of choice. Not only does temperature resistance increase with each material, but chemical resistance increases as well. In addition, PVDF is becoming the primary choice for water applications that use ultraviolet (UV) light or ozone as a water treatment method.

Next in line is application. The user must determine where and how the fitting or tubing will be used. The designer wants to take full advantage of all of the features a particular fitting has to offer, being careful not to over- or under-design. For example, even though a PVDF fitting may be certified to ANSI/NSF Standard 51—Food Equipment Materials and will function in a cold water application, it may be more “fitting” (and expensive) than that particular connection requires.

The following question is sometimes overlooked: With what is the fitting or tubing going to come in contact? In some cases, the media governs what fitting or tubing you can or cannot use.

For example, if a cold water system requires that a 15 percent sodium hypochlorite solution be used for disinfection, the installer cannot use acetal due to the materials’ inability to stand up to the 15 percent solution. Polypropylene would be the logical material choice, taking advantage of the good chemical resistance that polypropylene has with sodium hypochlorite.

It’s important to note that the combination of temperature and media may impact the performance of a product as well. Chemical compatibility tables are widely published on the Internet by materials suppliers and numerous manufacturers.

The last question to be addressed is the system pressure requirement. Typically, one won’t expect to see pressures greater than 125 pounds per square inch (psi) in a residential RO application. Using under-rated tubing or fittings can result in catastrophic failure of the tubing or fitting. The element of pressure, along with media and temperature, is critical to your peace of mind in system design since higher temperatures often reduce acceptable pressure performance.

Remembering to address the five basic issues in STAMP can save both installers and users a lot of aggravation. If you should have any questions, call your local valve and piping distributor for assistance.

About the authors
Tom Raguz is product engineer for the Plastic Products business unit of the Parker Hannifin Parflex Division in Ravenna, Ohio. Jackie DeThorne is a member of the same division, serving as business unit manager. Both are responsible for design, production and sales of plastic tubing and assemblies, fittings and valves made at the plant near Cleveland. Precautions to consider when selecting connectors are discussed in the Parker Hannifin Safety Guide, Bulletin 4400-B.1 (found at w The company’s polypropylene TrueSeal® fittings can handle up to 125 psi, while its acetal or PVDF fittings have a 300 psi working pressure. Raguz and DeThorne can be reached at (330) 296-2871 or (330) 296-8433 (fax).


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