System for controlling clarification of boiler feed water and the like

In combination with a system for controlling clarification of boiler feed water and the like by precipitation, said system comprising

• a settling tank having an inlet and an outlet for said water,
• means for adding a chemical to said inlet water to cause said precipitation,
• a drain line and first valve means for drawing off precipitate from the bottom of said tank,
• a small sampling line connected into said tank at a predetermined level above the bottom of said tank for continuously sampling water from said tank,
• means for continuously measuring turbidity of said sampled water, comprising
• a switch having a closed position if said turbidity exceeds a predetermined minimum and an open position if not, and
• means for backwashing said precipitate draw-off, comprising
• a second valve means for controlling flow through a connecting line between said inlet water and said drain line while said first valve means is closed,
• timing and control means for checking said turbidity at first predetermined intervals and for activating said first valve means for second predetermined intervals if said turbidity exceeds a predetermined minimum and for activating said second valve means with disabling of said first valve means at third predetermined regular intervals,
• said timing and control means comprising
• first timing means for opening said first valve means for said second predetermined intervals,
• first circuit means for connecting said turbidity switch to said first timing means for activating said first timing means only when said turbidity exceeds said predetermined minimum
• second timing means for checking said turbidity at said first predetermined intervals,
• second circuit means for connecting said second timing means to said first timing means for activating said second timing means whenever said turbidity switch is closed, and
• third timing means for opening said second valve means at said third predetermined regular intervals.