Patent ID: 7555899

Claim:
A control apparatus for a hydraulic pump, which delivers into at least one working line a displacement volume of a flow which is adjustable by an adjusting device, wherein the adjusting device is loadable with an actuating pressure by an actuating pressure connection, which is controlled by a control valve as a function of a first pressure and a second pressure, wherein a first pressure line has the first pressure load a first measuring surface and a second pressure line has the second pressure load an opposed second measuring surface of a volumetric flow control valve and wherein the first pressure is higher than the second pressure, wherein a pressure chamber is formed between the first and the second measuring surface and a leakage path connects the pressure chamber to the second pressure line, wherein the pressure chamber is connected by a counterpressure line to the first pressure line, while also being arranged separately from the actuating pressure connection, and wherein said pressure chamber has the form of an annular chamber with a first delimiting portion and a second delimiting portion, each said portion having an oppositely oriented surface, which surfaces are equally sized for preventing any force from displaying a piston of the volumetric flow control valve.