Patent ID: 6951103

Claim:
In a hydraulic control arrangement for a mobile operating machine including a lift boom, a tool mounted to an end of said boom for adjustment about a pivot axis, at least one hydraulic cylinder coupled between said boom and said tool for selectively adjusting the tool, a directional control valve coupled to first and second pressure chambers of said hydraulic cylinder for controlling the path of the pressurized fluid between said pressure chambers and a source of fluid pressure and a tank, a safety valve being inserted between said directional control valve and said first pressure chamber of said cylinder for preventing movement of said cylinder in the event of a rupture in a hose connected between said directional control valve and said safety valve, said safety valve including a valve element that can be opened to permit flow to said first pressure chamber so as to reposition said cylinder and a pressure accumulator being connected, or connectible, with said first pressure chamber of said cylinder, the improvement comprising: said pressure accumulator being connected to said first pressure chamber of said cylinder exclusive of any working components of said safety valve; said valve element of said safety valve being a two-position, pressure responsive valve which is normally biased to a first position wherein said valve element blocks fluid flow in the direction of said direction control valve from said first pressure chamber, and which shifts in response to pressure to a second position wherein it establishes a flow path to said direction control valve; said valve element being coupled at least to said first pressure chamber so as to be shifted to said second position in response to an increase in pressure in said first pressure chamber caused by pressurizing said second chamber; and a remotely controllable, two-position second safety valve being coupled in parallel with the first-mentioned safety valve and including a second valve element normally located in a first position blocking fluid flow to said direction control valve from said first pressure chamber, and being selectively movable to a second position establishing a fluid path between said first pressure chamber and said directional control valve, whereby flow to and from said first pressure chamber may be increased by selectively shifting said second valve element to said second position during actuation of said cylinder.