This document provides basic requirements for piston type hydraulic linear actuators for industrial valve, both double acting and single acting, used for on-off and modulating control duties. It includes criteria, method and guidelines for design, qualification, corrosion protection, control and testing. It does not apply to hydraulic actuators which are integral parts of control valves. Other requirements, or conditions of use, different from those indicated in this document, are expected to be subject to negotiations, between the purchaser and the manufacturer/supplier, prior to order.