This part of ISO 9635 specifies construction and performance requirements and test methods for control valves, intended for operation in irrigation systems with water at temperatures not exceeding 60 °C, which can contain fertilizers and other chemicals of the types and concentrations used in agriculture. It is applicable to hydraulically-operated control irrigation valves of DN 15 (1/2 inch) diameter or greater, designed to operate in any position, from fully open to fully closed. The valves can either be directly operated (i.e. the force applied via a spring or diaphragm to the obturator), or pilot-operated (i.e. the force is applied through an adjustable pilot valve via a diaphragm).