Valve history-packing it in

PACKING IT IN

Valves that have shafts or stems that move in and out of the pressure envelope require a packing to keep the pressure contained inside the valve. These packings must be flexible, reasonably resilient and able to withstand the highest temperature the valve will see in service. Early packing materials were rope derivatives such as jute and flax. But as operating temperatures rose, these materials proved inadequate. The answer was found in a unique mineral called Chrysotile, which gave us asbestos.

The long fibers of asbestos combined with its temperature resistance made it an outstanding packing and gasket material. Asbestos packing was installed in virtually all commodity steel valves from the 1920s through the 1980s. The material was superior for forming and filling the packing or stuffing box area, and it provided an excellent seal. Unfortunately, some of the same characteristics that made asbestos good packing, such as its fiber shape and size, also made it an unwelcome resident in the human lung. Since virtually every valve manufacturer used asbestos packings or gaskets, all of them have been drawn into lawsuits involving asbestos litigation and mesothelioma.

The replacement of asbestos packing and gaskets took some time, as immediate replacement materials did not work well. Finally, the industry perfected carbon/graphite-based products that have now been the norm for nearly 25 years when high-temperature packing and gasket materials are required.

For low-temperature applications, Teflon is an excellent corrosion-resistant sealing material. Teflon packing and gaskets are standard in today’s nickel alloy and stainless-steel valves. Teflon is also used for other valve components such as ball valve seats. The history of Teflon and ball valve seats is itself an intriguing tale but that tale is for another article.