Where Rubber Meets Water: Picking the Best Rubber Parts for Your Application

May 1, 2007
Depending on what part of the water and hydronics industry you’re in - production of drinking water systems, industrial makeup, process or cooling water, or wastewater - there are different variables to consider when selecting rubber components for your equipment.
Diaphragms for water pressure compsensating tanks in sizes from 8" to 26" in diameter.
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by Dave Pentland

Depending on what part of the water and hydronics industry you’re in - production of drinking water systems, industrial makeup, process or cooling water, or wastewater - there are different variables to consider when selecting rubber components for your equipment. These components can include manhole connector boots, pipe seals, check valves, diffuser membranes, and well and expansion tank diaphragms.

Sealing solutions.
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In the potable water industry, a key issue in rubber part selection is a need to keep water safe and clean. Likewise, in industrial and wastewater treatment, a major consideration is whether the rubber will stand up over time to a range of caustic materials and harsh conditions. Variables in each end of the water/hydronics industry spectrum are discussed here, setting basic guidelines to help select the right rubber parts for your application.

Thirsting for a Solution

Potable water isn’t what it used to be - and that’s a good thing. Stringent standards are designed to ensure drinking water is purer, cleaner and safer than ever. This means all parts and materials in contact with this water have to meet environmental standards, including those set by organizations like ASTM and NSF International in the United States, WRAS in England, ACS in France, and other governing bodies globally.

Often a requirement for parts used by these industries, NSF Standard 61 defines the amount and type of contaminates permitted to migrate into drinking water. It applies to components or materials that contact drinking water such as water coolers, ice makers and municipal drinking water equipment - to name a few - but also includes plumbing and municipal distribution systems. Standard 61 is now referenced by most American and Canadian plumbing standards as well as the Uniform Plumbing Code, International Plumbing Code and National Standard Plumbing Code.

It’s important to work with a manufacturer that’s up to date on the latest developments in these codes and standards, not just in the United States but globally. A recent example is new tighter odor/taste restrictions in France’s ACS. A manufacturer involved in producing parts to meet these standards initiated a new series of intense tests whereby its rubber materials spent days soaking in water. These tests exaggerate any potential real-world conditions to meet any concerns customers may have about how products affect drinking water’s taste or smell.

Right stuff for wastewater

The ability to be flexible and custom-tailor compounds is also important to wastewater applications. One compound definitely doesn’t fit all, when you may be dealing with a range of corrosive chemicals and climatic conditions. Different materials are better for certain uses: Neoprene is well-suited for an oil environment, silicone can stand up to extreme heat and cold, EPDM is the right starting point where the product is exposed to water and daylight.

Sealing boots for water, automotive, construction and telecommunications markets.
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Still, that’s just the start of your selection process. Often, an application calls for a custom engineered and molded solution with engineers involved from the project get-go. For example, an aeration equipment customer needed a newly formulated wastewater diaphragm, as its existing diaphragms were shrinking over time. After an extensive analysis, engineers determined an excessive amount of chlorine in the water was attacking the rubber compound and creating the gradual distortion. They addressed this by reformulating the plasticizer and reducing its quantity while maintaining the material’s plasticity.

When considering a provider for your hydronics application, look beyond the products themselves. Consider the company’s experience and capability. Does it have the correct equipment to produce the part without subcontracting? Can it produce parts at the required volume and for projected cost within the timeframe specified? Also, is it working with the most advanced rubber technologies, as opposed to outdated compression and transfer molding methods? And does it have a team of experienced engineers on staff to research, test, design and formulate advanced rubber technologies, or will it have to go outside for this capability?


Finally, it’s important a rubber part has the expected service life. A company with the capability to conduct rapid cycle testing to simulate real-world use can help ensure this. And of course, it should support its solution with some type of guarantee - or warranty.

A rubber manufacturer must be able to adjust curing systems, tweak formulations and make changes to molding processes to significantly reduce almost any residual material in drinking water or to handle any wastewater or other environmental conditions.

Thus, when the water meets the rubber, it may be important to look beneath the surface and examine the manufacturer’s ability to engineer, design and mold a solution that meets the specific unique needs of your application. Otherwise, you could be up a creek without a paddle.

About the Author: With 30 years of experience in rubber molding, Dave F. Pentland is president and owner of Jefferson Rubber Works Inc., of Worcester, MA. Contact: 508-791-3600 or [email protected]

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