| 摘要 |
A valve device disclosed for use in an oil or gas well, in order to actuate a valve between closed and open configurations. The valve device has a bore with a piston member axially moveable in the bore between first and second configurations. The piston is urged to move axially between the first and the second configurations within the bore by fluid pressure applied to the piston, and the axial movement of the piston from the first to the second configuration under the force of the fluid pressure is opposed by the force of a spring device. The piston is urged by a magnetic force to move axially from the first to the second configuration in the same direction as the force applied by the fluid pressure, and against the force of the spring device. The magnetic force applied to the piston when the piston is in the first configuration is less than the magnetic force applied to the piston when the piston is in the second configuration, so that as the piston approaches the second configuration under the force of the fluid pressure, the magnetic force increases as the piston moves under the force of the fluid pressure, whereby the magnetic force and the fluid pressure together overcome the force of the spring device to move the piston into the second configuration. |
