The triple offset design completely eliminates any rubbing action of the sealing elements during the 90 degrees of rotation and such capability, combined with other key features, have effectively positioned over time the Vanessa Series 30,000 as the ultimate process valve.
Thanks to our engineering expertise, state-of-the-art technology and manufacturing capabilities, Emerson Vanessa has provided for decades an extremely reliable triple offset valve capable of delivering full shut-off and peace of mind operation over a wide range of temperatures and pressure classes. All Vanessa triple offset valves rely on the principles of metal-to-metal, torque seating and non-rubbing, quarter turn rotation.
Triple Offset Design
The Vanessa Series 30,000 valve shares the same cone-to-cone principle with a globe valve, but sealing is performed by quarter turn rotation. TOVs use a sealing system consisting of a stationary seat and a rotating sealing surface sharing an identical shape: an inclined conic section. When these cones overlap, closed position is reached and sealing occurs. Such ‘quarter turn globe’ concept is made possible by the use of three ‘offsets’ meant to completely eliminate rubbing. Optimized seating angles and rotational characteristics guarantee superior tightness via an ingenious combination of the triple offset design and a flexible metal seal ring across all basic, cryogenic and high temperature configurations.
Offset 1 – The shaft is placed behind the plane of the sealing surface to provide a continuous seat path.
Offset 2 – The shaft is placed to one side of the pipe/valve centerline to allow the displacement of the seal from the seat during the 90° opening.
Offset 3 – The seat and seal cone centerlines are inclined in respect to the pipe/valve centerline. This third offset completely eliminates rubbing.
Vanessa’s seating force is generated by externally applied torque rather than by mechanical interference as in position-seated ball, butterfly and plug valves. This means that the cone-to-cone sealing occurs by contact pressure and not by friction generated by the elastic deformation of the seat. This feature allows our valve to handle high pressure classes and provide reliable and highly controlled operating torque. Our trim design, seating angles and surface finish all contribute to a very low, consistent and predictable torque demand which is unaffected by fluid temperatures and pressures throughout the valve life. The non-rubbing rotation ensures low and constant running torque across the 90 degree rotation so that the operating torque calculated and tested on a newly manufactured product is equal to a comparable fully operational valve.
Metal-to-metal sealing ultimately ensures that the valve can handle virtually all possible temperatures, pressure levels and fluid types. We use a Stellite® grade 21 seat and a resilient seal ring in Duplex as a minimum with high mechanical resistance. Stellite® 21 is a cobalt alloy that coats the body seat to provide hardness, resistance to fluid abrasion, corrosion and general wear. Due to its unique design, the metal seal ring has elastic properties which allow for radial compression to be uniformly distributed around the seating surface. These are key contributors to the zero leakage performance of the valve.
Stellite® is a registered trade name of Deloro
Quarter Turn Rotation
A quarter turn rotation means significantly lower and more consistent running torque compared to any rising stem design, ensuring that Vanessa TOVs can achieve extremely quick stroke times. This also eliminates any negative effects on packing caused by rising stems, such as extrusion and abrasion, and ultimately provides for a more compact valve design.
Eliminating contact between seat and seal during opening-closing means extending the life of the sealing elements and the valve altogether. This also combines with the main feature of quarter turn rotation, i.e. low and consistent running torque, for which valve operation remains quick and easy over time and modulating is possible even at extremely low angles. The ability of handling quick stroke time requirements and a high number of cycles is also correlated to the valve non-rubbing feature. Users can ultimately reap the critical benefit of longer lifecycle of the sealing elements compared to other valve designs.