A fluid system for a pump circuit, in particular a hydraulic high-pressure pump circuit, has a function block. An input arm assembly is provided with interchangeable vacuum leads such that package-to-package conversion only requires replacing the vacuum lead with a different size vacuum lead. The restrictor cross-sections A of both flow restrictors D1, D2 having a variable cross-section of a hydraulic damping assembly S in a regulating system S of a variable displacement pump P can be varied simultaneously and oppositely according to an imminent specification of the system set by the manufacturer. Characteristics may be sensed by mechanical sensors, electrical sensors, optical sensors, acoustic sensors, gyroscopic sensors, or a combination thereof. A second resilient element is provided between the arresting member and the third gear bracket.