Valve assembly and a hydraulic actuator comprising the valve assembly

Abstract

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