US Patent 7810321 Relief pressure switching apparatus for hydraulic working machine

In a relief pressure switching apparatus for hydraulic working machine for switching a relief pressure of a hydraulic actuator circuit in accordance with a specification of a compression crushing apparatus or a breaker to be installed, electromagnetically variable relief valves for determining the relief pressure are provided, and a controller commands the relief pressure selected by an operator from a plurality of relief pressures preliminarily set and stored in combination with a flow rate as matching a working apparatus to the relief valves.