Energized seal resists aggressive media

March 2, 1998 Design News

DESIGN APPLICATIONS From the regional editors

AT THE NATIONAL DESIGN ENGINEERING SHOW

Energized seal resists aggressive media

Combines best features of spring-energized seals and PTFE-based materials

Charles J. Murray, Senior Regional Editor

Broomfield, CO--For most design engineers, the toughest sealing applications are those that involve aggressive media. Acids, paints, and even certain types of foods can wear out conventional rubber seals. Unfortunately, materials that can stand up to aggressive media often lack the elasticity to maintain a positive seal over a long period of time.

Now, however, engineers from American Variseal have found a solution to those problems. The company's new Capseal^TM combines the memory of rubber with the ability to stand up to aggressive media.

The Capseal accomplishes this by employing an "energized seal" design. It consists of three basic parts: a PTFE-based Turconr jacket; a Turcon cap; and a stainless steel cantilever beam spring.

In use, the steel spring provides the elastic energy to maintain a positive seal. It fits within the Turcon jacket, and pushes against its walls, supplying outward sealing pressure. The Turcon cap fits over the top of the assembly, and protects the steel spring from potentially aggressive fluids. Specially designed lips on the cap and jacket engage one another and positively close the assembly.

The combination of the steel spring and the surrounding Turcon cap provides users with the best features of two different types of sealing materials. "PTFE-based materials don't have the memory required to keep themselves energized against the hardware," explains Gary Henderson of American Variseal. "But when you place a stainless steel spring inside of them, you permanently energize the seal while still getting the performance of PTFE-based materials."

Henderson says that the Capseal is best used in moderate-speed rod and piston applications. Its advantages in those applications are threefold. It's ideal for clean-in-place applications, because it prevents users from having to disassemble machinery when they clean it out. Second, it prevents particles from becoming trapped in spring tabs, which potentially could cause contamination problems in food-related applications. Third, it prevents degradation of the spring, lowering the risk of contamination and increasing the ability to maintain performance over time. Applications for the seal include pumps, food processing systems, and beverage machinery. It is particularly well-suited for beverage machines, because users can easily wash it down with minimal hardware disassembly. For that reason, one of the seal's most popular uses is clean-in-place applications, engineers say.

"It's designed for applications where you can't expose the metal to the media being sealed," Henderson says. "With this design, you can get the sealing advantages of a metal spring in applications where you couldn't use metal before."

Additional details?Contact Technical Services Dept., American Variseal Corporation, 510 Burbank St., P.O. Box 1479, Broomfield, CO 80038, (303) 469-4874, http://www.variseal.com.