TECHNICAL ARTICLE
Dixon Headquarters in Chestertown, Maryland.
The Role of Bellows Sealed Valves
According to the EPA, 62 % of total emissions at a typical facility come from valves. These numbers are not trivial; any effort to reduce emissions from valves goes a long way. One of the challenges in reducing fugitive emissions is that industrial valves operate under dynamic conditions. The valves are subjected to wear and tear over time, making it difficult to maintain a long-term seal without leaks. However, there is a robust, reliable solution to the challenges posed by fugitive emissions – bellows sealed valves.
Bellows sealed valves are designed to address the limitation of conventional valve designs, particularly in high-risk applications where fugitive emissions must be minimized. The bellows seal expands and contracts like an accordion as the valve stem moves up or down, enabling precise control of the valve while maintaining a tight, leakproof seal. Unlike conventional valves that rely on gland packing to seal the stem and bonnet, bellows sealed valves use welded connections. The bellows is welded to both the stem and the valve body, creating a seamless barrier that prevents leaks, even in high-pressure or corrosive environments. Since bellows sealed valves do not rely on packing material, which degrades over time, they require less frequent maintenance and repair. Less maintenance means having more time to make products, which ultimately has a positive impact on uptime and operational costs.
One major problem with traditional packed valves is their tendency to loosen up in applications with a lot of thermal cycling. Opening and closing the valve causes rapid wear on the packing and leads to leakage of hot transfer fluids or steam. In contrast, bellows sealed valves require no adjustment, are durable, and can withstand high-pressure, high-temperature, and corrosive environments, ultimately providing a longer service life. Installing bellows sealed valves in the hottest section of the thermal loop eliminates the chance that a leak will cause a serious safety hazard.
There are two ways to manufacture bellows: hydroforming or edge welding. Hydroforming involves pressurizing a metal tube into metal folds, while edge welding essentially welds a series of washer-like plates to form the accordion shape. Both methods form a bellows seal that completes the same task. However, hydroformed bellows are typically larger and take up more space than welded bellows.
There is a common misconception that hydroformed bellows are stronger and will last longer because they incorporate fewer welds, but as long as edge-welded bellows are designed and fabricated correctly, and qualified to the MSS SP-117 standard, the service life should be the same.
When specifying a bellows sealed valve for a particular application, it is imperative to consider media / corrosion resistance, temperature rating, pressure rating, and cycle life. Standards such as ISO 15848-1, ISO 15848-2, API 622, API 624, and API 641 should be consulted during the selection process. These specifications ensure bellows sealed valves are tested rigorously for performance under challenging conditions, significantly reducing the likelihood of leaks.
It is important to note that there are low emissions non-bellows valves designed to minimize fugitive emissions. While these valves may meet regulatory standards or EPA requirements for emissions control, they depend on correct installation, can require adjustment, may have a shorter lifespan, and do not completely eliminate leaks. Therefore, in a critical application requiring absolute sealing, a bellows sealed valve with zero emissions is ideal.
APRIL 2025 • FUGITIVE EMISSIONS JOURNAL 27