| 摘要 |
A self piloted check valve which utilizes closure of a piloting flapper valve to permit development of closure forces for a ball valve. The normally open ball valve has a central flow passage and simultaneously rotates and translates as it traverses between its fully open and fully closed positions. An opening bias system utilizes a combination of a first less stiff spring and a second stiffer spring. Reversible decoupling means disconnects and reconnects the second spring at a short travel distance from the normally open position of the ball, while the first spring always provides opening bias forces to the ball. The pressure induced force required to fully close the ball valve following decoupling of the second spring is more than the force required to overcome the combination of the first and second springs. Additionally, while the secondary spring is engaged, hydrodynamic damping of the ball opening movement is provided. |
