PURPOSE: To prevent the jamming of an outer slide member by constantly connecting a circumferentailly extending pressure slot which receives the fluid generating the pressure between an inner slide member and the outer slide member, with a control connecting portion through a release passage. CONSTITUTION: An inner bore 3 is formed in a housing 2, and a pump channel, a tank channel 7 and the first and second control channels are respectively connected with a pump connecting portion, a tank connecting portion and the first and second control connecting portions by this order in the inner bore 3. An outer slide member 4 is rotatably mounted in the inner bore 3, an inner slide member 5 is rotatably mounted in the bore inside in the axial direction of the outer slide member 4, and a circumferentially extending pressure slot 12 for receiving the fluid which generates the pressure between the inner slide member 5 and the outer slide member 4, is formed. The pressure slot 12 is constantly connected with the control connecting portion 6 through a release passage, whereby the jamming of the outer slide member 4 can be prevented.
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