Patent GB-898694-A (GB)
Title: Improvements in or relating to hydraulic drives for electric switchgear
IPC: B30B15/18
Filed: 1961-02-24
Abstract: 898,694. Hydraulic apparatus. MASCHINENFABBIK OERLIKON. Feb. 24, 1961 [March 1, 1960], No. 6924/61. Class 69 (2). An hydraulic drive for electrical switchgear comprises a pressure supply circuit A, Fig. 1, a control circuit C and a working circuit B, the working circuit having an hydraulic working cylinder 13, a working valve 16, an hydraulic cut-in accumulator 17 and an hydraulic cut-out accumulator 14, whereby the drive is arranged to provide storage of energy from the cut-in step for effecting the cut-out step. The cylinder 13, which has a piston connected to the switchgear, is connected at its opposite ends to the accumulators 14, 17 which are separated by a choke 18. The valve 16 is disposed between the cylinder 13 and the cut-in accumulator 17 and comprises left- and right-hand sides which are in the form of check valves connected to a manifold 7 and return line 30, respectively, and are alternately opened to the line 15 from the cylinder 13 by operation of an element 19 responsive to pressure pulses from a preliminary control valve 21 which also consists of left- and right-hand check valves and connects a line 20 from the element 19 alternately to a line 7a from the manifold and the line 30 leading to a reservoir 4. The preliminary control valve is operated by an element 27 responsive to pressure pulses from a hand-controlled valve 29 or pilot valves 23, 24 actuated by electromagnets 25, 26 selectively energized to effect the cut-in and cut-out of the switchgear. The manifold 7 is connected to a pump 2 driven by an electric motor I and a hand pump 8, the pressure in the manifold being controlled by pressure-responsive switches 11, 12 controlling the motor and a pressure-relief valve 10 ; the pressure in the manifold is indicated on a micrometer 9. In operation, the manifold and cut-in accumulator 17 are charged to a pressure determined by the switch 11, the right-hand half of the valve 16 acting as a check valve for the accumulator 17 and the left-hand half connecting the line 15 to the return line 30. When a cut-in signal is received by the electromagnet 26, the pilot valve 24 opens to permit a pressure pulse from the manifold 7 and a line 7a to pass to the element 27 along a line 28a to open right-hand check valve and close the left-hand check valve of the valve 21 so that a pressure pulse from the manifold and line 7a passes along a line 20 to the element 19 to close the left-hand check valve and open the righthand check valve of the valve 16, whereby the pressure from the cut-in accumulator 17 passes through line 15 to the lower end of the cylinder 13 to move its piston and operate the switchgear. The liquid displaced from above the piston changes the cut-out accumulator 14. The choke 18 eventually permits the pressure across the cylinder to be equalized. When a cut-out signal is received by the electromagnet 25, the condition of the check valves in the valves 16, 21 is reversed to disconnect the cut-in accumulator 17 from the line 15 which is then connected to the return line 30 so that the pressure in the cutout accumulator returns the piston in the cylinder 13 and the switchgear to their original positions. In other arrangements, more than one working valve 16 is provided in the working circuit, each valve controlling a pair of working cylinders having associated cut-out and cut-in accumulators and all the working valves being mechanically interconnected for operation in unison. Alternatively, the valves may be hydraulically interconnected, throttles being provided in the circuit so that pressure pulses arrive at the elements 19 simultaneously. The working valves 16 consist of a piston 43, Fig. 4, forming the element 19 and having a rod 44 which, when the piston is subjected to the pressure in the manifold 7, displaces a conical member 45 from a seat 47, which together form the right-hand check valve, and, at the same time, presses a conical member 49 against a seat 51, which together form the lefthand check valve, so that the line 15 connected to the port 40 is disconnected from a port 39 leading to the return line 30 and connected to a port 41 leading to the cut-in accumulator 17. When the pressure is released from the piston 43, the pressure in the manifold, which is joined to a port 42, and the pressure in the line 15 reverses the positions of the members 45, 49 so that the accumulator is disconnected from the line 15 which is then connected to the return line.  Two working cylinders 80, Fig. 6, and a cutout accumulator 14 may be mounted on a common housing 60 having a pipe 61 leading to the line 15. The cylinders 80 are supported at one end in the housing and at the other in sleeves 78 secured by spring means 74, 75 to tubes 69 secured to the housing by rings 70 and flanged cases 71. Each cylinder has a piston 82 having dampers 83, 84 and movable in one direction by the pressure in the pipe 61 and in the opposite direction by pressure in the cut-out accumulator passing through a bore 66, a space between the tube 69 and cylinder 80, and ports in the wall of the cylinder. In an alternative construction of working cylinder, a check valve consisting of a sleeve 90, Fig. 7, bored cone 92 and control piston 95 is disposed between the bore 61 and the interior of the cylinder 80. During the cutting-in step, the liquid from the bore 61 passes through the bore in the cone to the cylinder. When the bore 61 is connected to the return line and the pressure in the accumulator moves the piston 82 in the opposite direction, the liquid displaced by the piston acts on the control piston to close the bore in the cone and the displaced liquid passes through passages 87, 86 to a line 89 which may lead to another part of the switchgear.