How is spool movement in a proportional valve controlled?

In a proportional valve, the movement of the spool is controlled in a way that is directly proportional to an electrical input signal. This means that the amount of movement of the spool—and consequently the flow of fluid or pressure in the system—can be finely adjusted based on an input signal, typically from a control device like a sensor or a controller.

When an electrical signal is applied to a proportional valve, it generates a magnetic field that moves the spool to a position that matches the magnitude of that signal. This allows for varying levels of flow control and pressure, enabling precise adjustments and efficient operation of hydraulic or pneumatic systems. Essentially, as the electrical input changes, the spool's position changes accordingly, facilitating a smooth and gradual response rather than abrupt shifts.

The other options do not accurately describe how spool movement is controlled in a proportional valve. Metering notches relate more to mechanical limiters or guides rather than direct control based on an electrical signal. System pressure is indeed a factor in the overall system dynamics but does not dictate the spool's position in a proportional context.