An automatic control valve is a fluid-regulating device that adjusts flow, pressure, temperature, or liquid level using internal hydraulic pilots or external power actuators without manual operation. Key types include globe valves, butterfly valves, and ball valves.
An air-to-open (ATO) control valve needs air pressure to push it open against an internal spring. If pressure is applied, the valve opens. It's in a "fail" position if control air pressure is fully lost (0 kPa).
Without air pressure to force the valve open, the internal mechanical spring takes over and pushes the valve stem back to its resting state.