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The Difference Between O-rings and Sealing Elements

April 7, 2020 Viega
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An important element of our fittings is only seen before installation and is invisible afterward.

The sealing elements, one at either end of the fitting, are often are confused with O-rings, which look similar but perform different functions.

The primary difference between the two is in their longevity and how they function. O-rings are installed as part of a dynamic seal, so that the O-ring can move with the assembly it is installed in, like a washer-less faucet.

Sealing elements are installed as part of a static seal, so that the element never moves once pressed.

Because O-rings move, they are subject to friction and wear and tear that comes with the movement. As a result, they wear out and must be replaced. Assemblies that O-rings are installed in are specifically designed to be taken apart so that the O-rings can be replaced. The frequency of replacement depends on the application, material, degree of movement and use.

By contrast, because sealing elements in press fittings are static, they function during the press but are not subject to motion during system operation. Therefore, they do not suffer the same wear and tear and do not have to be replaced. They are permanent once pressed and designed to outlast the fitting they are installed in.

Viega offers three types of sealing elements: EPDM, HNBR and FKM. Each has its own applications and specifications:

EPDM: Ethylene-propylene-diene monomer rubber (EPDM) is a synthetic, cured all-purpose elastomer with excellent resistance to chemicals and other harsh environmental conditions. With operating temperatures from 0℉ to 250℉, it is suitable to any type of water application (hot water included), as well as compressed air and ketones.

HNBR: Hydrogenated nitrile butadiene rubber (HNBR) is a specialty-purpose elastomer with a great deal of strength and retention in the face of heat, oil and chemical exposure. HNBR sealing elements are primarily geared toward gas applications, from natural and propane to mixed and manufactured gases, along with oils and lubricants.

FKM: is a specialty-purpose elastomer. In combination with excellent resistance to chemicals and environmental influences, it is resistant to extreme spikes in temperatures (up to 356℉) for 24 hours or less. These qualities make it suitable for industrial environments with harsh, corrosive conditions.

At Viega, we are equally confident in the quality of our sealing elements and our fittings. That’s because we pair quality design and manufacturing processes with weathering tests to ensure sealing elements perform as intended well into the future.

Operating within our approved conditions, our sealing elements carry the same warranty period as the product line they are installed in. For example, our standard ProPress fittings are backed by a 50-year limited warranty. We stand behind the ability of our sealing elements to meet these same demands.

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