Head loss vs. run time
Expected media head loss = Carman-Kozeny clean bed (anthracite 0.6 m over sand 0.3 m, at the live rate and water viscosity) + deposit head loss from the stored solids (UFRV × 1.5 × run-average settled NTU, k 2.58 m per kg/m²). Dots: measured media head loss this run; the line is the model along the run. Red line: terminal head loss, where the PLC starts the backwash.
Filtered turbidity over the run
Filtered-water turbidity (on-line turbidimeter) and particle count since the last backwash: the ripening peak during filter-to-waste, the stable run, and breakthrough when the bed is full. Red: 0.3 NTU (US EPA IESWTR 95th-percentile limit, also the PLC backwash trigger); amber: 0.15 NTU warning.
Filter cell
Settled-water inlet and wash troughs, water over the bed, anthracite over sand, the I.M.S. cap (in place of gravel) and the Type S underdrain, and the pipe gallery (effluent, backwash water, air scour, waste), with live instrument values. Red = beyond the twin's alarm limit.
Condition sensors
Bars against the alarm limits in the twin file (red line).