877,322. Hydraulic apparatus; fluid-pressure servomotor control systems. LEDUC, R. July 5, 1960 [July 7, 1959], No. 23418/60. Classes 69 (2) and 135. A double-acting fluid-pressure jack comprises a piston 1, Fig. 1, movable in a cylinder 3 and having formed therein a feed duct 4 and an exhaust duct 6 connected to feed and exhaust ports, respectively, and a control rod 10 which is coaxially slidable in the piston and carries means 8, 9 for opening and closing the ports, the ports being so positioned that movement of the control rod in either direction from a neutral range of position in which both ports are closed brings about movement of the piston in the opposite direction. The piston is, on the right-hand side, permanently connected to a supply line 2 and, on the left-hand side, which is of larger area than the right, is alternatively connected to the supply, by way of the feed duct 4 and a duct 5, and exhaust, by way of the duct 5 and exhaust duct 6. Movement of the rod 10 to the right from the position shown connects ducts 5 and 6 together to move the piston to the left, the movement continuing until the piston reaches its end position or the rod is moved rapidly to overtake the piston and close the ports. In another embodiment, the ports are closed by balls 8a, 9a, Fig. 2, which are displaceable from their seatings by cams 11, 12 on the control rod. In an embodiment wherein the two faces of the piston are of equal area, the feed and exhaust ports are duplicated and the control rod has four cams controlling balls in the ports. The arrangement shown in Fig. 2 may be incorporated into a system for controlling the pressure in an accumulator (not shown) which is connected by a one-way valve to a line 31, Fig. 6, in a housing 20 having a line 30 connected to a pump and a line 32 connected to exhaust, communication between the lines 30, 32 being controlled by a ball valve 29. The pressure in the accumulator is connected by a line 22 to a chamber 21 in which is a partition 23 urged against the accumulator pressure by a spring 24. The control rod 27 of the jack is connected to the partition, and, when the pressure in the accumulator has dropped to a predetermined value, a cam 35 on the rod opens a ball valve 36 to permit the accumulator pressure from line 22 to act on the left-hand face of the piston which moves to the right permitting the valve 29 to close and disconnect the pump line 30 from the exhaust line 32. When the pressure in the accumulator reaches a predetermined maximum value, the movement of the partition 23 causes a cam 33 on the rod 27 to open the ball valve 34 and the accumulator pressure to move the piston 28 to the left, opening the ball valve 29 to connect the pump line 30 to the exhaust line 32. The distance between the cams 33, 35 is such as to permit considerable travel of the control rod in its neutral position without actuation of the balls 34, 36. The arrangement shown in Fig. 2 may be incorporated in an assembly having an accumulator consisting of a piston 42, Fig. 8, on its righthand side connected to a source of compressed gas and on its left-hand side connected by a coupling 44, 53 to the control rod 45 of the jack. The left-hand side of the piston 42 is also hydraulically-connected by a one-way valve 48 to a line 47 leading from a pump, a ball-valve 50 being moved by the jack piston 46 to control the communication between the pump line 47 and exhaust line 49. In a further embodiment wherein the accumulator pressure is connected by a line 31, Fig. 13, to one side of the jack piston 28 and to a line 31a leading to apparatus, such as an electric circuit breaker in a transmission line or a gate in a hydro-electric system, operated by the pressure in the accumulator, communication between a pump line 30 and an exhaust line 32 is controlled by a by-pass valve consisting of a sleeve 29 on the piston 28 which is urged to the right by a spring 62. The pressure of the accumulator acts on the end 60 of the control rod 27 to press the rod against a partition loaded by a spring 24. When the pressure in the accumulator drops to a predetermined level, the spring 24 moves the rod 27 to open a ball-valve B and connect the right-hand side of the piston to an exhaust passage 37 and the exhaust line 32, the accumulator pressure moving the piston to the right closing the valve 29 so that the pump charges the accumulator through a one-way valve 61. When the pressure in the accumulator reaches a predetermined value, the control rod is moved to open ball-valve B and the piston moves to open bypass valve 29 and connect the pump line 30 to the exhaust line 32. A further cam 64 is provided on the control rod to open valve B together with valve A to relieve excess pressure in the accumulator.