Hydraulic system with fluid flow summation control of a variable displacement pump and priority allocation of fluid flow

A system (20) has a variable displacement pump (50) that supplies pressurized fluid to power a plurality of hydraulic functions (31-36). Each hydraulic function has a control valve (51-56) with a variable source orifice (64) controlling fluid flow between the pump and a flow summation node (74), and a variable metering orifice (75) controlling fluid flow between the flow summation node and a hydraulic actuator (21-26). Variable bypass orifices (8a- 8f) in the control valves are connected in series between the flow summation node and a tank (48). As the metering orifice in a control valve enlarges, the source orifice enlarges and the bypass orifice shrinks. This alters pressure at the flow summation node, which is used to control the output of the pump. Components are provided to give selected hydraulic functions different levels of priority with respect to consuming fluid flow from the pump.