Wedge wire resin traps and underdrain nozzles play complementary roles in ion exchange system protection. Underdrain nozzles are installed inside the vessel to support the resin bed and ensure even flow distribution, while wedge wire resin traps are located downstream to capture resin beads that escape due to abnormal conditions https://www.johnsonwedgewire.com/news/wedge-wire-resin-trap-vs-underdrain-nozzle.html