Abstract: In a swash plate piston motor (2), a piston (24, 41) which is caused to reciprocate by a fluid pressure and a cylinder block (23) which rotates within an operating chamber (21) in accordance with the reciprocation of the piston (24, 41) are accommodated in the operating chamber (21) inside a case (30). When the cylinder block (23) rotates through inertia after a supply of working fluid to a working fluid passage (11, 12) for applying the fluid pressure to the piston (24, 41) has been shut off, a check valve (18) supplies working fluid in the operating chamber (21) to the working fluid passage (11, 12) through a communicating passage (14) if necessary. As a result, the interior pressure of the fluid pressure motor (2) is prevented from becoming negative, and the piston (24, 41) is prevented from floating up from a swash plate (25).

Abstract: A relief valve includes a high-pressure port (14) communicating to a hydraulic circuit (41), a low-pressure port (15) communicating to a drain circuit (42), a valve (11) supported so as to be movable in back and forward in the axial direction thereof to open and close between these ports (14, 15), a piston (12) supported so as to be movable in the coaxial direction in relation to the valve (11), a spring (13) interveningly provided between the valve (11) and the piston (12) for biasing the valve (11) to a valve closing direction against the pressure of the high-pressure port (14), a damping chamber (20) defined at back side of the piston (12), pressure guiding paths (26, 27) for guiding the pressure in the upstream side of the valve (11) to the damping chamber (20), and a plurality of orifices (30a to 30d) exchangeably arranged in series in the pressure guiding paths (26, 27).