| 摘要 |
A device for use in actuating a valve to control the flow of fluids through a flow tube comprises a stationary ring surrounding the flow tube, the ring having an inner diameter greater than an outer diameter of the flow tube. An interior of the ring and an exterior of the flow tube have complementary screw threads. At least three actuators are equally circumferentially spaced along an exterior of the ring. When activated an actuator induces a screw thread on the interior of the ring to engage a screw thread on the exterior of the flow tube such that the flow tube is moved in an axial direction relative to the ring. |
