HYDRAULIC CONTROL APPARATUS

摘要

Disclosed are methods and apparatus for controlling the flow of hydraulic fluid to and from a work cylinder. The disclosed system includes a reversible variable displacement pump interconnected between a work cylinder and a selector valve which may connect the pump with any of a plurality of fluid reservoirs. The fluid reservoirs contain hydraulic fluid at variable pressures so that the pressure at the work cylinder may be raised to pressures well above the pressure differential capacity of the pump at maximum flow rate by selectively increasing the pressure on the reservoir side of the pump. The system includes means for controlling the pressure at each port of the pump so that the pressue on the output port is always greater than the pressure on the input port regardless of the direction of flow through the pump and regardless of pressures at other points in the system. Relief circuits are provided to prevent system overloading, to prevent overloading of the pump and to protect against overloading the lift apparatus employing the hydraulic system of the invention.