What activates the plate and nozzle type pressure controls in a proportional valve?

The plate and nozzle type pressure controls in a proportional valve are activated by the proportional solenoid. This solenoid plays a crucial role in regulating the flow of hydraulic fluid by modulating the position of the spool within the valve, which in turn influences the pressure output. When electrical current flows through the proportional solenoid, it generates a magnetic field that moves the spool to a specific position. This action allows for precise control over the hydraulic pressure based on the magnitude of the electrical input, enabling a variable response to changing system demands.

In contrast, oil pressure, air pressure, and manual levers do not directly activate the pressure controls in a proportional valve. Oil pressure is often a result of the valve's function, whereas air pressure is unrelated to hydraulic systems involving proportional valves. Manual levers can be used to operate some types of valves, but they do not provide the precision and automation that a proportional solenoid offers in controlling pressure dynamically. Therefore, the proportional solenoid is the correct and most effective means of activating the plate and nozzle type pressure controls.