Valves for use in irrigation systems include a moveable sealing member disposed within a valve body. The moveable sealing member is configured to close automatically the valve when the magnitude of a pressure differential between the inlet and the outlet of the valve body reaches a predetermined threshold value and to open automatically the valve when the magnitude of the pressure differential falls below the predetermined threshold value. Irrigation systems include such valves and methods for flushing debris out of the irrigation systems using such valves.