Positive flow control system

Abstract

A positive flow control system is provided that uses open-centered control valves in a series connection to provide priority between different fluid circuits and to provide requested flow regardless of the load pressure while minimizing unused or wasted flow. This is accomplished by providing a restriction in the last open-centered control valve to controllably restrict the flow therethrough when the valve is in its neutral position and having the source of pressurized fluid at a minimum displacement position that substantially matches the rate of flow across the restriction. A controller controls the displacement of the source of pressurized fluid and the displacement of the respective open-centered control valves in proportional to the respective input commands. Initial movement of the last open-centered control valve closes off the restricted flow thereacross to the reservoir prior to the source of pressurized fluid being communicated to the associated actuator. The subject system provides priority control and an effective control of wasted fluid while providing the needed flow rate regardless of the load without needing a special control arrangement for priority or separate bypass valve to control wasted flow.