Development of a ball valve with PVD coated metal-to-metal sealing mechanism

Conventional ball valves are based on elastomeric sealing technologies which exhibit restricted wear resistance in the presence of network impurities while requiring high operating torques. In the described investigations, the elastomeric sealing of a 2-inch floating ball valve was replaced by a metal-to-metal seating for attaining specific application requirements, without major dimensional changes. In order to avoid the use of elastomerics and achieve a high performance rating of the valve (Class VI shut-off), computational fluid dynamics (CFD) simulations were employed to predict the optimum contact geometry of ball/seating. A high accuracy contact was obtained through precision turning of the hardened metal shell (ball seating) and by grinding of its counter ball body. Both components, ball and seating, were appropriately heat treated and subsequently coated with a nanostructured diamond like carbon (DLC) coating, applied by physical vapour deposition (PVD) techniques, providing superior surface strength characteristics and nearly frictionless operation. Nanoindentations provided information regarding the coatings properties, while nanoimpacts were employed to determine the impact abrasive wear of the developed components.