Yes, type "U" refers to Unknown for the Nominal Annual Rate.
是的，“U”型指的是未知的名义增长率。
2
J41N Type PN40 steel globe valves: manual, flanged, straight-through, the valve seat sealing surface material as nylon plastic, nominal pressure PN40, carbon steel valve body material cut-off valve.
Nominal diameter and flow valves, basically the same breath for full-bore type, Circulation than nominal diameter valve is given. it small called non-reducing type.