Proportional control valve that continuously controls hydraulic fluid flow rate and pressure in proportion to input signals in hydraulic systems. Achieves stepless adjustment of spool position and opening degree according to electrical signals (voltage/current), enabling precise speed control and positioning control. Used in manufacturing equipment requiring high-precision control such as screw speed control in injection molding machines, feed rate control in machine tools, and pressing force control in press machinery. Differs from servo valves in response speed and cost, with proportional valves being widely used in general industrial machinery. Classified into flow proportional valves, pressure proportional valves, and directional proportional valves, available in feedback-equipped and open-loop types.