A hydraulic arrangement is described comprising a lifting cylinder 10 for
a lifting arm 12 pivotably mounted on a vehicle. A hose 22 selectively
connects a working chamber 10a of the lifting cylinder 10 to a supply 16
and a return 18 line to raise and lower the lifting arm, respectively. A
safety check valve 46 is connected between the hose 22 and the working
chamber 10a to maintain the working chamber under pressure and avoid
collapse of the lifting arm 12 in the event of rupturing of the hose 22.
An accumulator 70 is connectable to the working chamber 10 of the lifting
cylinder 10 by way of the safety check valve 46 to provide ride control.
A solenoid 50 overrides the operation of the safety check valve 46 while
the hose 22 is isolated from both the supply 16 and the return 18 line to
allow fluid to flow in both directions between the accumulator 70 and the
working chamber 10a to cause the lifting cylinder to act as a spring
supporting the weight of the lifting arm. A pressure switch 82 prevents
overriding of the operation of the safety check valve 46 if the pressure
in the hose 22 should drop below a threshold.