Patent GB-651789-A (GB)
Title: Improvements relating to hydraulically operated machines
IPC: B30B15/16
Filed: 1947-11-20
Abstract: 651,789. Control of motors. LAMB, H. Nov. 20, 1947, No. 30767. [Class 38(iii)] [Also in Group XXIX] An electric motor actuates a displaceable valve member in a hydraulic valve controlling the supply to and return of liquid from a reversible hydraulic motor for operating lifts, cranes, jiggers or presses and limited displacement of the valve member is brought about in one direction or in the other direction by the electric motor consequent upon manual operation of a first or second control switch respectively and the return of the valve member to a neutral position is effected by the electric motor upon release of the first or second control switch. The Figs. show a portion of the control gear of a hydraulic lift. A hydraulic control valve 11 includes a displaceable valve member which when displaced to the left, Fig. 1, may, for example, cause pressure in an operating cylinder of the lift to be released thereby allowing the lift to descend while displacement of the valve member to the right causes the pressure in the operating cylinder to be increased by connecting it to a source of hydraulic pressure thus displacing the piston therein and causing the lift to ascend. The valve member 13 is operated by a nut 14 to which it is connected, the nut working on a thread 15 which can be rotated in one or other direction by an electric motor 18 according to whether electromagnetically operated clutches 19, 20 are operated. When the control valve reaches the limit of its travel in either direction it engages one of two limit switches 32, 33 to open the circuit therethrough. Also one of two selector switches. 37, 38 is operated by a projection 34 attached to the nut 14 engaging with one or other of two arms 35, 36. In Fig. 2, 40, 41, 42 represent gate interlock switches through which a circuit is completed upon closure of a gate with which it is associated. The armature 50 and field 51 of the motor 18 are thus energized from mains 130, 131 when the switches 40-42 are closed. Depression of an up control switch 110 brings about operation of the electromagnetic clutch 19, and causes the valve member to move to the right bringing about raising of the lift cage. At the end of the travel of the valve member the switch 33 is opened and the clutch 19 released. Upon releasing the up control switch a circuit is completed through contacts 112 for operation of the main down contactor switch. Operation of the latter brings about energization of the operating coil 102 of the clutch 20 whereby the valve member 13 is moved to the left. When the member reaches its central position lever 36 is disengaged and switch 38 operated so that the circuit to the coil 102 is discontinued. The control switches 110 and 120 may be in the form of spring-loaded push-button switches or a single control handle may operate both of the switches 110 and 120. Overtravel protection for the lift cage may take the form of a stop valve actuated by means of an endless cord extending through the height of the life well and having two bobbins secured thereto, one at the top and one at the bottom of the travel of the lift adapted to co-operate with an arm projecting from the lift cage. When the arm makes contact with either of the bobbins the endless cord is displaced up or down as the case may be and the stop valve is actuated. The Provisional Specification refers to use of a reversible electric motor.