This specification covers the design, construction, testing, and operating requirements for self-contained pressure-reducing valves for air or nitrogen systems. Pressure-reducing valves shall be either: type I - inlet outlet end connections of the same pressure rating or type II - outlet end connection pressure rating lower than the inlet end connection rating. Valves shall incorporate the design features specified. Pressure-reducing valves shall meet the performance requirements prescribed. Hydrostatic shell test, seal tightness test, and external leakage test shall be performed to meet the requirements prescribed.