Below is a list of Hydraulic Proportional Valves manufacturers from North Sioux City, South Dakota. Hydraulic proportional valves are parts that manage fluid flow and pressure within a hydraulic system. They are a kind of electric valve similar to solenoids and servovalves and consist of a wire coil and a movable plunger. They are called proportional because the output flow is not equal to the input flow. The force is balanced between a mechanical force supplied by a spring in the valve and a magnetic force provided by a current passing through a coil of wire around the valve.