This is the Hayward replacement Molded Flow Cell for CAT and HCC pool chemistry controllers. This replacement flow cell is used to create a small body of sample pool water for the two probes to test from. Pool water is connected into this flow cell and passes over the probes and back into the pool.
It can also be used as a manual pool water testing point. Purchase the accessories to this flow cell separate such as the valves, probes and tubing.