Abstract: A safety circuit for preventing uncontrolled descent of a hydraulically supported load, in the event of a leak, comprises parallel hydraulic pressure feed lines, control valves in these, and means responsive to a difference in pressure between the lines and arranged to close the valves when such a pressure difference is detected. The valves are provided adjacent to a lifting cylinder or cylinders and close to the pressure source, so as to prevent spillage of hydraulic fluid as well as to prevent descent of the supported load.

Abstract: A hydraulic press has lowering and lifting cylinders, a controlled pressure-limiting valve connected to the high-pressure hydraulic supply, and a shuttle valve with its operating inlets connected respectively to the hydraulic supply and to the lifting cylinders and its outlet connected to the pressure-limiting valve to control it. Further valves responsive to a disturbance of hydraulic equilibrium in the hydraulic circuit operate switches controlling the hydraulic fluid supply.

Abstract: An overload safety device for a hydraulic press of the type in which a parallel linkage is mounted on the moveable beam to ensure normal accurate alignment if constituted by an operating rod mounted preferably on the transverse connecting rod of the parallel linkage in order to operate limit switches in accordance with longitudinal dimension changes due to compressive or tensile forces in this connecting rod arising from asymmetrical load. The operating rod can be arcuate and mounted at each end on the connecting rod or can be straight and mounted at one end only. Flexing of the arcuate rod or relative movement of the free end of the straight rod can be magnified by a mechanical linkage with an arm operating the limit switches.