Patent ID: 7448208

Claim:
A hydraulic arrangement comprising: double acting lifting cylinder, having first and second working chambers and piston faces of different sizes, for a lifting arm pivotably mounted on a vehicle, a first hose for selectively connecting the first working chamber of the lifting cylinder to a supply line and a return line to raise and lower the lifting arm, a first safety check valve connected between the first hose and the first working chamber, a second hose for selectively connecting the second working chamber to the supply line and the return line, a second safety check valve connected between the second hose and the second working chamber, an accumulator connected to the first working chamber of the lifting cylinder by way of the first safety check valve, and a respective electrically actuated solenoid for overriding the operation of each of the safety check valves while either hose is isolated from both the supply and the return line and allowing fluid to flow in both directions between the accumulator and the working chamber to cause the lifting cylinder to act as a spring supporting the weight of the lifting arm, wherein a pressure sensitive switch, arranged to inhibit the supply of current to the respective of each overridable safety check valve monitors the pressure in the connection between the accumulator and the lifting cylinder and prevents the overriding of the operation of the safety check valve when the monitored pressured drops below a threshold.