The simplest form of tablet chlorinator, shown in Figure 1, consists of a rectangular plastic container with an inlet baffle to spread the inflow across its width and a vertical slot at the other end forming the outflow. The container lid is pierced to take a vertical tube, slotted at the lower end, which stands on the floor of the container and holds a stack of tablets. Water flowing through the chamber dissolves the tablets. As this arrangement, if applied directly to the full flow, produces much higher dose rates than would normally be required, a by-pass system is needed to allow only a controlled proportion of flow to pass through the doser. This by-pass is the only control of dosing in a tablet doser; the unit itself is not adjustable.
Figure 1. Simple tablet chlorinator
Most box chlorinators are capable of a minimum dose of about 60 mg/l chlorine per minute and are therefore not appropriate for water flows of less than 3.6 m3/hour.
Operation and maintenance
Hypochlorite tablet dosers are often purchased from the suppliers of the tablets themselves. The manufacturers' guidelines regarding operation and maintenance should be followed. In general this will require:
• Regular, frequent topping up of the tablet reservoir.
• Regular, but less frequent, cleaning out of the apparatus and lines of accumulated precipitates, scale, and such like.
• Regular frequent monitoring of residual chlorine in the distribution network, and adjustment of the dose control on the vertical tube and by-pass system accordingly.