Backwash Cycle
Once hardness breaks through, the softener must be regenerated. In down-flow units, the resin must first be backwashed to loosen the resin (it becomes compacted by the weight of the water), and to remove any other material that has been filtered out of the water by the resin. The backwash rate is normally 6 to 8 gpm/square foot of zeolite bed area. The operator needs to apply enough backwash water to expand the resin bed by about 50 percent. The backwash water is usually discharged to a box containing orifice plates that measure the flow rate. Distributors at the top of the unit provide for uniform water distribution and uniform wash-water collection. Underdrains provide uniform distribution of the backwash water on the bottom of the resin.