How it works
- the exchange — Each resin bead carries fixed negative sites loaded with sodium. Calcium and magnesium have a stronger affinity, so they displace the sodium and stay behind. The water leaves soft, with a little more sodium than it arrived with.
- the service run — An exchange zone forms at the top and travels down, exactly like the carbon bed. Above it the resin is exhausted, below it still in sodium form. The run ends when that zone reaches the underdrain and hardness appears in the outlet.
- regeneration — Strong brine reverses the equilibrium by sheer mass action — flood the resin with enough sodium and the calcium comes off. Chemistry says roughly 117 g of salt per litre of resin at full capacity; in practice you use two to three times the stoichiometric dose, because the last of the calcium is the hardest to shift.
- leakage and salt — Under-dose the regeneration and calcium is left on the resin at the bottom of the bed — exactly where the treated water leaves. That shows up as hardness leakage during the next run. Pull the salt dose down and watch leakage climb.
- what governs it — Resin volume and feed hardness set the run length; salt dose sets leakage and running cost; service velocity decides whether the exchange has time to happen at all. Salt and water quality are the same dial, turned in opposite directions.
Design parameters
The panel opposite runs the same correlations as the IX-900 design sheet, so the animation and the calculator cannot disagree. Drag any of them and the picture responds.
- Flow — m³/h
- Feed hardness — mg/L CaCO₃
- Resin volume — L
- Operating capacity — g CaCO₃/L
- Salt dose — g NaCl/L resin
- Vessel diameter — m
Open the full IX-900 design sheet for the governing equations, the accepted design envelopes and the worked calculation.