This standard specifies hydraulic internal control sequence valves, external control sequence valves, internal control one-way sequence valves, external control one-way sequence valves and their variants - internal control balance valves, external control balance valves, unloading valves, one-way unloading valves, Basic parameters, technical requirements, test methods, inspection rules and markings, packaging, transportation and storage requirements for sequential back pressure valves. This standard applies to downstream valves with threaded connections, plate connections and superimposed connections that use hydraulic oil or other liquids with equivalent performance as the working medium.