Abstract: A turning-purpose hydraulic circuit characterized in that a discharge passage (20a) of a hydraulic pump (20) is connected to a variable relief valve (21) and a pump port of a directional switching valve (22); a first actuator port and a second actuator port (25, 26) of the said directional switching valve are connected to a turning-purpose hydraulic motor (27); the pilot pressure of a pilot valve (33) is introduced into pressure chambers (31, 32) for controlling a spool in the said directional switching valve and is also introduced into a pressure chamber (40) for controlling a set pressure in the said variable relief valve; a metering-in side portion (42) along which a pressurized oil flows from the said pump port of the said spool to the first or second actuator port is formed with a portion having a configuration such that a flow force may not be produced thereat; and a metering-out side portion (45) along which the pressurized oil flows from the first or second actuator port of the said spool to a tank po

Abstract: A directional change-over valve which has a valve body having connecting surfaces at both sides thereof, a spool slidably inserted into the valve body, a check valve replaceable depending upon utilities thereof, wherein the valve body has a plurality of valve chambers, the central valve chamber is communicated with the hole for mounting the check valve for removably mounting the check valve, passages are provided opening at the connecting surfaces of the valve body in the respective valve chambers, another passages are provided for connecting the interior of the check valve to the both side valve chambers to form parallel, tandem and series circuits. Thus, this invention simplifies the structure and circuits to provide a compact directional change-over valve device as a whole.