Triple Offset Seat Seal For Butterfly Valves Enables Leak-Free Shut-Off

A proprietary process, developed by EGC Enterprises, eliminates the typical surface imperfections that can cause leakage in triple offset butterfly valves.

Manufacturers of triple offset butterfly valves (TOBV’s) focus on achieving leak-free shut off, especially for valves in bi-directional service. A unique, new process developed at EGC Enterprises, Inc. eliminates troublesome burrs and surface imperfections on the face of TOBV Seat Seal Discs to allow true leak-free shut off.

The typical laminate construction of TOBV seat seal discs use dual alternating layers of rigid metal and compressible and resilient material such as flexible graphite or other gasket sheet. This make up offers the flexure and resilience necessary to seal against the rigid valve seat when closed into position by the offset stem. While this composite structure is very advantageous, the alternating layers of hard and soft materials present a challenge to machinists working to craft the complex geometry required into a perfectly machined seat seal disc surface that will achieve leak-free sealing.

“Flexure, resilience, and surface finish are each critical to leak-free service as TOBV seals are compressed radially against the valve seat by torque applied to the valve’s offset shaft,” says Vice President, Jeff Bernthisel. EGC’s new TOBV Seat Seal production accomplishes just this. By maintaining the burr-free surface of the metal layers on the seal face and ensuring uniform elasticity, the circumference of EGC’s TOBV seat seal is evenly loaded achieving the tightest shut-off with the least amount of shaft torque and less actuator effort.

Testing by a major triple offset valve OEM has proven EGC TOBV Seat Seals provide positive bi-directional shut-off for >10,000 cycles. EGC TOBV seat seals are fire safe, seal at pressure classes to 900 lb. and in temperatures ranging from cryogenics to 1200°F, and are the only approved product of their type for use in US Standard Navy Valves triple offset butterfly design.

EGC uses a wide range of metals for the rigid layers including stainless steels, duplex and super-duplex alloys, inconel, monel and hastalloy. Resilient layers include Thermafoil and Grafoil flexible graphite, along with other compressible gasket sheet materials. All materials offer excellent chemical resistance and allow for use in extreme temperature service.

TOBV seat seals from EGC can be used in all high-performance applications including power generation, petro-chemical and refining and can be certified for nuclear plant service.