Abstract: Disclosed is an attachment mounting/demounting device for working machinery by which a pin of an attachment held in engagement with an engagement groove of the mounting/demounting device can be surely locked and operation for locking and unlocking the pin can be easily performed. The mounting/demounting device comprises a latch capable of switching over between a release posture allowing a first pin to come into and out of a first engagement groove and an engagement posture preventing slip-off of the pin fitted to the engagement groove, a lock piston capable of switching over between a lock posture locking the latch in the engagement posture and an unlock posture releasing the latch from the lock posture, and a biasing spring for always biasing the lock piston toward the lock posture.

Abstract: The invention intends to provide a relief valve which can prevent malfunction caused by generation of negative pressure lowering the minimum pressure to be originally maintained by a load circuit.Maloperation of a relief valve 401 is prevented by allowing a check valve 423 for preventing a backflow from a main valve element 410 and pilot valve element 412 side to a load port side 402 to be intervened at a pressure chamber 408 between a load port 406 connected to a load circuit, a main valve element 410, and a pilot valve element 412 and by applying a hydraulic lock when negative pressure lower than the minimum pressure to be originally maintained by a load circuit is generated. And by communicating a downstream chamber 425 downstream of the check valve 423 to a return port 407 with a reset oil passage 429 which is opened and closed by a reset valve 430, the hydraulic lock is designed to be released.

Abstract: An overload preventive device is capable of preventing elevation of preload pressure due to sticking action or break-through load of a hydraulic cylinder of a press machine. A delay valve for opening when the internal pressure of the load detecting circuit is lower than the minimum pressure to be maintained continuously over a specified time is interposed between a hydraulic pump for supplying pressurized oil of a specified pressure to a load detecting circuit.

Abstract: An attachment detaching apparatus for hydraulic shovels includes a bracket pivoted, through an arm pin and a link pin, respectively, on a tip end of the arm of the hydraulic shovel. Guide grooves are provided with the opening portion being notched into the bracket. An oscillating arm where the opening portion has a notch located on the side opposite to the guide groove or the sliding slider is provided in a location opposite to the guide groove. An opening, closing apparatus for opening or closing the oscillating arm or the sliding slider is provided, the opening, closing apparatus is driven in the engaging direction by the engagement of a pin A of the attachment with the guide groove of the bracket and of a second pin B with the notch of the oscillating arm or the sliding slider so as to retain the attachment. A rotating hook, capable of grasping the pin A, is pivoted on the bracket through the rotating shaft.

Abstract: The invention relates to a relief valve and intends to provide a relief valve designed to improve response and operational stability. In an overload prevention safety device in which a main valve element including a pilot valve element in a valve case is arranged, a pilot valve is opened by oil pressure exerted on the pilot valve element from an oil passage formed in the main valve element while resisting to an energizing means for energizing the pilot valve element. By this operation oil pressure is exerted on the pilot valve element side of the main valve element to open the main valve. An oil passage is designed to be constructed in holes with different diameters with a small-diameter section, a taper section, and a large-diameter section continuously arranged in that order. A pilot valve seat is sealably in contact with the pilot valve element mounted at the connections between the small-diameter section and the taper section.