This valve being mounted in the water distribution pipes with its pilot valve being pre - setted in a fixde flow - rate which enable the pressure variation of the main body ' s upper - reach not to have an effect on the flow volume of the outlet 本阀安装于送配水管路中,可预先设定其上之导向阀于某一固定流量,使其主阀进口压力变化而不会影响出水口。