| 摘要 |
A valve assembly (2) forming a bridge circuit and a hydraulic actuator comprising at least one valve assembly (2) are disclosed. The valve assembly (2) is fluidly connectable between a fluid source (3) and a fluid drain (4). The valve assembly (2) comprises a first valve (8) fluidly connected between the fluid source (3) and a first diagonal point (12) of the bridge circuit, a second valve (9) fluidly connected between the fluid source (3) and a second diagonal point (13) of the bridge circuit, a third valve (10) fluidly connected between the first diagonal point (12) and the fluid drain (4), and a fourth valve (11) fluidly connected between the second diagonal point (13) and the fluid drain (4). The valves (8, 9, 10, 11) are such that in the case of a power cut off, flows of fluid away from the diagonal points (12, 13) are prevented. Thereby a hydraulic servomotor (5) connected across the diagonal points (12, 13) will be hydraulically locked in its instantaneous position, and a safety feature is accordingly provided. The first valve (8) and the second valve (9) are furthermore of a kind which is closed in an energized state. Thereby it is possible to control the valve assembly (2) in such a manner that a piston member (14) of a servomotor (5) connected across the diagonal points (12, 13) can be moved at a high velocity, thereby providing a servomotor (5) having a quick response time.
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