One-Piece Packing Design Enhances Ball Valve's Thermal Performance

EQUIPMENT TECHNOLOGY

Swagelok Co. (Solon, OH; www.swagelok.com) has enhanced its 40 series one-piece instrumentation ball valve, a workhorse that has served the chemical industry for over 40 years, to address customer requirements for a wider range of operating temperatures and improved performances under thermal cycling conditions. The result, launched at ChemShow (New York; Nov. 1-3, 2005) under the 40G moniker, features working pressures up to 3,000 psig (206 bar) and temperatures from -65 to 300�F (-53 to 148�C); a two-way valve configuration for shut-off service in both a straight and angle pattern; and a three-way valve for switching service. With equivalent dimensions to the 40 series (1/16-3/8-in. and 3-8-mm end connections), 40G valves are dimensionally interchangeable with their predecessors for drop-in field service.

The versatility of Swagelok's 40G series is related directly to its seal design, which includes: (1) an encapsulated patent pending single-piece packing to improve leak resistance and optimize sealing pressure; (2) enlarged, equal-sized trunnions to reduce the amount of packing material; (3) a live-loaded packing system that reduces the need for packing adjustment and improves thermal cycle performance; (4) modified polytetrafluoroethylene (PTFE) packing material (referred by Swagelok as TFM), which exhibits higher resistance to cold-flow deformation during thermal cycling vs. standard PTFE. "The ball and trunnion portion of the valve ball stem are encapsulated in a single-piece packing that is subsequently pressed into the valve cavity, creating a functional seal without the need for system pressure. "This design reduces potential leak points and allows bi-directional flow," notes Mike Adkins, Swagelok product manager.

The next step of the assembly process is the placement of a packing gland over the upper trunnion to rest directly on top of the packing material. With a close fit around the trunnion and within the valve cavity, the gland fully contains the packing material, thereby preventing it from extruding during thermal cycling. The upper and lower trunnions also better align the valve element within the valve cavity and provides more directed, balanced loading on the packing for improved sealing.

A patent-pending direct-load assembly method is another factor in the 40G series' consistent, enhanced performance from valve to valve. It eliminates torque from the assembly process and allows for repeatable application of a predetermined load. This combined with a series of springs allow the valve to function in a repeatable manner over a thermal cycle range. As the temperature drops, the packing contracts and the springs maintain the sealing load on the packing. As temperatures rise, the packing expands, pushing up on the gland, and in turn, the springs compress. "The load is also more likely to be retained during valve actuation, which means users will have less need to adjust the valve in the field," says Adkins.