Abstract: An improved hydraulic servo-valve including a spool (10, 10R, 10L) adapted to slidably move in a valve body (1) to change the direction of flow of a working liquid and vary a flow rate of the working liquid, nozzle back-pressure chambers (18, 18R, 18L) to which a pilot pressure is applied for displacing the spool (10, 10R, 10L), and a flapper mechanism comprising nozzles (19, 19R, 19L) and flappers (20, 20R, 20L) is disclosed. Static pressure bearings (14R, 14L, 141R, 141L, 142R, 142L) are formed at opposite ends of the spool (10, 10R, 10L). In addition, the hydraulic servo-valve is formed with passages extend from a pump port (P) to the nozzle back-pressure chambers (18, 18R, 18L) via the static pressure bearings (14R, 14L, 141R, 141L, 142R, 142L).

Abstract: A pressure control valve for maintaining a control pressure constant even if the flow rate of pressurized oil varies, and an oil supply apparatus adapted for a turbo machine using this pressure control valve. The pressure control valve drives a throttle valve by a hydraulic cylinder through the operation of the piston of the cylinder by a guide valve. A port is formed so as to throttle and release the oil at the input side to control the pressure at the inlet side of the valve, oil from the output side for controlling the pressure is guided to the guide valve, and the cylinder communicates with an oil pressure source through the guide valve. An oil supply apparatus which has this pressure control valve guides a pilot tube leading from the header which feeds to the load side of the guide valve, and guides the pressurized oil from the conduit between the pressurized oil supply source to the header and to the throttle valve, thereby releasing the pressurized oil to an oil tank.