Patent ID: 7849686

Claim:
A hydraulic circuit comprising: at least one valve assembly forming a bridge circuit and being fluidly connectable between a fluid source and a fluid drain, the valve assembly comprising: at least one first valve fluidly connected between the fluid source and a first diagonal point of the bridge circuit, said at least one first valve being a valve which is normally open in a de-energized state, at least in a direction from the fluid source towards the first diagonal point, at least one second valve fluidly connected between the fluid source and a second diagonal point of the bridge circuit, said at least one second valve being a valve which is normally open in a de-energized state, at least in a direction from the fluid source towards the second diagonal point, at least one third valve fluidly connected between the first diagonal point of the bridge circuit and the fluid drain, said at least one third valve being a valve which is normally closed in a de-energized state, and at least one fourth valve fluidly connected between the second diagonal point of the bridge circuit and the fluid drain, said at least one fourth valve being a valve which is normally closed in a de-energized state, and a hydraulic servomotor having a first chamber fluidly connected to the first diagonal point and a second chamber fluidly connected to the second diagonal point such that the valve assembly controls flow in and out of the first and second chambers to move the hydraulic servomotor, wherein the valve assembly retains the position of the hydraulic servomotor in the event that a failure is detected.