US Patent 7222484 Hydraulic system with multiple pressure relief levels

A hydraulic system has at least one primary hydraulic functions and a plurality of secondary hydraulic functions all of which are connected in parallel to a supply conduit and a return conduit. A first pressure relief valve prevents pressure in the supply conduit from exceeding a first limit and second pressure relief valve prevents the pressure at the secondary hydraulic functions from exceeding the lower second pressure limit. Novel pressure relief circuits are provided which enable only two pressure relief valves to provide one of two pressure limits at more than two hydraulic functions.