Abstract: A pressure selector valve (13) is provided between a hydraulic motor (1) and a directional control valve (5) to connect one of the main conduits (4A), (4B) on a high pressure side to a high pressure conduit (14) while connecting the other of the main conduits on a low pressure side to a low pressure conduit (15). As an inertial body approaches a stop position, a spool valve (16) is switched to an open position (e), bringing a branch passage (14A) of the high pressure conduit (14) into communication with the low pressure conduit. When the pressure difference between the main conduits becomes small, the pressure selector valve is automatically returned to a neutral position to cut off communication between the main conduits, suppressing a reversing movement of the hydraulic motor so that an inertial body can be brought to a stop smoothly.

Abstract: A pressure selector valve (13) is provided between a hydraulic motor (1) and a directional control valve (5) to connect one of the main conduits (4A), (4B) on a high pressure side to a high pressure conduit (14) while connecting the other of the main conduits on a low pressure side to a low pressure conduit (15). As an inertial body approaches a stop position, a spool valve (16) is switched to an open position (e), bringing a branch passage (14A) of the high pressure conduit (14) into communication with the low pressure conduit. When the pressure difference between the main conduits becomes small, the pressure selector valve is automatically returned to a neutral position to cut off communication between the main conduits, suppressing a reversing movement of the hydraulic motor so that an inertial body can be brought to a stop smoothly.

Abstract: A hydraulic motor capable of minimizing a wear caused on a rotating brake disk of a brake device, wherein a rotating brake disk (32) which forms a plurality of arc-shaped grooves (17) apart from each other in circumferential direction and constitutes a brake device (31) is provided on the outer peripheral side of a cylinder block (15), and a plurality of arc-shaped projections (33) engaged with the arc-shaped grooves (17) and a plurality of radial contact parts (34) are provided on the inner peripheral side of the rotating brake disk (32) and the plurality of radial contact parts (34) are allowed to face the outer peripheral surface of the cylinder block (15) so that they can be brought into contact with each other, whereby, at the time of braking of the hydraulic motor (10), the movement of the rotating brake disk (32) in rotating direction is controlled by the arc-shaped projections (33) and the movement of the rotating brake disk (32) in radial direction is controlled by the radial contact parts (34).

Abstract: A hydraulic drive system comprises a check valve cb1 for detecting a pressure on the outlet side of a pressure compensating device VB1, a maximum load pressure detecting line SL1 for selecting higher one of the pressure detected by the check valve cb1 and a load pressure of an actuator associated with a hydraulic pump P1 and supplying it as a signal pressure, a check valve cb2 for detecting a pressure on the outlet side of a pressure compensating device VB2, a maximum load pressure detecting line SL2 for selecting higher one of the pressure detected by the check valve cb2 and a load pressure of an actuator associated with a hydraulic pump P2 and supplying it as a signal pressure independently of the maximum load pressure detecting line SL1, and a passage 300 for joining hydraulic fluids supplied from the hydraulic pumps P1, P2 and passing through variable restrictors RB1, RB2 with each other and supplying it to an actuator B. Mutual independence between the two hydraulic pumps P1, P2 can be thereby ensured.

Abstract: An inertial body drive mechanism which is arranged to prevent a reversing motion of a hydraulic motor 1 after an inertial rotation and which is capable of stopping the hydraulic motor 1 quickly together with an inertial body. An oil chamber 26 of a reversing motion preventive valve 21 and an oil reservoir chamber 34 of an oil suction feeder 32 are communicated with each other through a tank conduit 27 with a throttle 38. Operating oil is supplied into and out of the oil chamber 26 by way of the oil reservoir chamber 34 of the oil suction feeder 32 in relation with displacement of a piston operating in response to oil pressure acting in a pilot chamber 33. When inertial rotation of the hydraulic motor 1 is once stopped, operating oil is supplied from the oil reservoir chamber 34 to the oil chamber 26 thereby sliding the reversing motion preventive valve 21 from a closed position (a) to an open position (b) to prevent reversing motions of the hydraulic motor 1.This application is a designated filing under 35 U.

Abstract: A hydraulic drive system for construction machines with an improved pressure compensating valve assembly comprising a first directional control valve (3, 5, 7) of closed center type connected in series with a second directional control valve (12) of open center type.