Patent US 4,199,944

A load responsive fluid power control system using servo type flow control valves and fluid motors supplied by a variable displacement pump. The pump displacement is either regulated by an electro-hydraulic control valve in response to an electrical signal proportional to motor load or the pump displacement is regulated to maintain a constant discharge pressure. The flow of pressurized fluid from the pump is automatically cut off from a servo type valve controlling a negative or aiding load once this load exceeds a certain minimum level and the inlet flow requirement of the actuator is supplied from a low pressure source bypassing the servo valve.