873,023. Hydraulic apparatus. INTERNATIONAL HARVESTER CO. Feb. 5, 1960, No. 4169/60. Class 69 (2). An hydraulic system for controlling a plurality of hydraulic motors 16, 20, 25, Fig. 1, from a single source of fluid pressure 10 comprises at least one control valve 14, 14a of the open-centre spool type and at least one successively-arranged control valve 23 of the closed-centre spool type associated with pressure regulating means 31, each valve having ports for connection to their associated hydraulic motors and the open-centre spooltype valve 14a having an outlet port 111a which is in communication with the pressureregulating means and is controlled so that when the valve is positioned to establish communication between its associated motor 20 and the source of fluid pressure, communication between the source and pressure-regulating means is interrupted, and vice versa. The open-centre valve 14 consists of a casing 86, Fig. 6, having flat parallel faces 95, 96, face 95 having inlet ports 104, 114 aligned with and, by means of recesses 103, 113, in constant communication with, outlet ports 105, 115 in the face 96. The flat faces permit the valve to be joined to adjacent valves so that the outlet ports of one valve are aligned with the inlet ports of an adjacent valve. The valve 14 also has outlet ports 100, 118 in a side face for connection to its motor 16 and an outlet port 111 in the face 96 for connecting fluid pressure at an inlet port 108 to an inlet port 108a of the adjacent valve 14a when the spool of the valve 14 is in its neutral position. The spool of the valve is movable, by a lever 138 having an arm 129 engaging a groove in the spool, from neutral position, in which it is resiliently held by a spring 154 and the ports 100, 118 are closed to prevent movement of the motor, to one or other of two positions for connecting either port 100 or 118 to the fluid pressure from the pump 10 to move the motor in one direction or the other, and in which positions the outlet port 111 is disconnected from the inlet port 108. When the spool of the valve 14 is in its neutral position and the spool of the valve 14a, which is similar to the valve 14, is also in its neutral position and not connecting the fluid pressure at its inlet ports 104a, 114a to its motor 20, the outlet port 111a of the valve 14a supplies fluid pressure from the inlet port 108a to an inlet port 47 of the closedcentre valve 23 and to the pressure regulator 31. The spool of the valve 14a is movable to a further position wherein the lines 21, 22 leading to its motor are both connected to exhaust so that the piston of the motor is free to float. The closed-centre valve 23 has a spool movable by a lever 37 to uncover one or other of ports 43, 44 and connect fluid pressure supplied to the inlet port 47, when the spools of the valves 14, 14a are in their neutral or float positions, to its motor 25. With the spool of the valve 23 in its neutral position, a port 42 connected to a line 28 leading from the regulator is closed and results in the pressure on each side of a throttle 65 being equal. This pressure acting on the piston 84 and a ball 82 of a blocking valve 60, lifts the ball from its seating so that the line 29 from the outlet port 111a to the inlet port 47 is connected to exhaust 32 and the pressure of fluid supplied by the pump is reduced to a value insufficient to operate the motor 25. When the spool of the valve 23 is moved, the port 42 is uncovered and connected to an exhaust port 48, the pressure differential across the throttle 65 increases and the drop in pressure in the line 28 causes the ball 82 to seat and the pressure supplied by the pump to increase sufficiently to operate the motor 25. Excess pressure in the line is relieved by a relief valve 73 in the pressure regulator 31. A further pressure relief valve 13, Figs. 1 and 13, is provided in an inlet manifold 12 in which the supply from the pump is connected to an inlet 172 leading to a chamber 170 having a passage 168, 169 communicating with ports 161, 162, 163 which are in a face adapted to be secured to the face 95 of the valve 14 and are aligned with the inlet ports 104, 108, 114. The chamber 170 also leads to a passage 173 having a member 182 urged to a lower position by a spring 185 in a compartment 174. Excess pressure moves the member 182 upwardly against the spring so that axiallyspaced passages 183 connect the chamber 170 to the compartment 174 and exhaust. In an alternative arrangment, an adaptor plate 208, Fig. 17, is interposed between the open-centre valve 14a and the closed centre valve 23. The plate has inlet ports 218, 220 aligned with the outlet ports 105a, 115a of the valve 14a and connected to a port 222 aligned with the inlet port 47 of the valve 23. A further port 224 is aligned with the port 111a of the valve 14a and is connected to the pressure regulator 31. In this arrangement, fluid pressure from the pump is always available at the inlet port 47 of the valve 23 so that the motor 25 can be operated by direct pump pressure irrespective of the positions of the spools of the valves 14, 14a. However, the valve 23 can also operate its motor in association with the pressure-regulating means 31 where the spools of both valves 14, 14a are in their neutral or float positions.