Patent GB-1210371-A (GB)
Title: Method and means for controlling the operation of hydraulically operated jacks
Inventor: EDWARDS HUGH JEREMY WILLIS
IPC: F15B21/08
Filed: 1967-10-06
Abstract: 1,210,371. Rod straining-ram. CCL SYSTEMS Ltd. 6 Jan., 1969 [6 Oct., 1967], No.. 45696/67. Heading F2G. A method of controlling an hydraulically operated jack having, or having associated therewith, a directional control.. valve 41 through which fluid is passed, from a pump 35 connected to a reservoir 36, to either side of the ram piston 2, and having a load cell 26, or other load. sensitive device, incorporated therein, comprises by-passing the hydraulic fluid back to the reservoir 36 at a position between the pump 35 and the control valve 41 when the load registered by the load cell reaches a desired value, and simultaneously preventing the return flow of pressurized fluid from the jack. As shown, the hydraulic jack comprises a stressing tube 1 which extends through seals 16, 21 into the annular space between a centre tube 14 and a main cylinder 20 and which has a piston 2 with seals 3 which slidingly engage the tube 14 and cylinder 20, the latter being connected, at one end, to the corresponding end of the centre tube 14 by the annular load cell 26. The other end of the centre tube 14 carries a barrel member 5 having a tapered bore 6 and arranged therein a number of radially disposed wedges 7 which are urged into an operative position by a compression spring 8 supported by a wedge cap 9. The barrel member 5 is slidingly received within a nose cone 4 which is secured to the outer end of the stressing tube 1, accommodates therein a wedge release tube 10, and has attached thereto a lock-off cylinder 11. The latter accommodates a wedge release tube 10 and receives a stressing nose 13 which is adapted to be placed in contact with a bearing plate of a concrete structure being stressed. Hydraulic fluid can be introduced either into a chamber 28 through a pipe 29 to extend the jack or, through a pipe 31, an annular passage 32, passageway 33 in the piston 2, and into an annular chamber 32 to contract the jack. In use the jack is positioned over the wire to be stressed and hydraulic fluid is passed along the line 29 into the chamber 28 so that the main cylinder 20 is moved outwardly relative to the stressing tube 1, the movement being transmitted, through the load cell 26 to the centre tube 14 which, with the barrel 5, is also moved outwardly. The outward movement of the barrel 5 allows the wedges 7 to move away from the release tube 10 and, under the action of the spring 8, to grip the wire to be stressed, further outward movement tensioning the wire until a predetermined load, governed by the load cell 26, has been applied and the movement ceases. In order to release the wire fluid under pressure from the line 31 is passed into the inlet 30 to the chamber 34 to move the tube 14 and the main cylinder inwardly, the wedges 7 releasing their grip on the wire. A low voltage control circuit, Fig. 2, not shown, can be operated either manually, or automatically, to extend or retract, the jack. The operation to extend the jack de-energizes the solenoid 38 of a dumping valve 37 so that hydraulic fluid is delivered by a pump 35 from a reservoir 36 to a pipe 40 which leads to a directional control valve 41 a spring-loaded solenoid 42 of which is energized to direct fluid to retraction line 29 and the line 31 to exhaust 68. A check valve assembly 44 is located between the valve 41 and the jack. When the required load is registered on a meter (62), Fig. 2, not shown, the solenoids 38, 42 are respectively deenergized and energized, so that fluid is bypassed through the exhaust valve 39 and the lack of pressure in the line 29 causes the check valve 45 to close and prevent loss of fluid from the chamber 28. To contract the ram the solenoids 38, 42 are de-energized, fluid flowing through the lines 40 and 31 to the chamber 32 and retraction of the ram not taking place until the pressure build up is sufficient to displace the check valve 45 and the chamber 28 to be connected to the exhaust 68. After the jack has been fully retracted the solenoid 38 is again energized so that the fluid from the pump 35 is by-passed to exhaust. In the case of automatic operation the load value is determined by a trip level controller (66), Fig. 2, not shown, which causes the de-energizing of the solenoid 38 and overrides the manual button (55).