Fluoridation downflow saturator

To ensure good handling and feeding characteristics for dry chemicals, it is important that the dry chemical adhere to graduation specifications. The size gradation for crystalline (coarse) sodium fluoride for use in a downflow saturator (see the Section 5) should be in the 20-60-mesh range (0.85-0.25 mm), and powdered sodium silicofluoride... 

A saturator produces a saturated solution by allowing water to trickle through a bed of coarse granular sodium fluoride solids in excess of the amount required for saturating the water solution. Two types of saturators are available upflow and downflow. In a downflow saturator, the sodium fluoride solids are isolated from the saturated solution by a plastic cone or a pipe manifold and a filtration barrier composed of layers of sand and gravel. The barrier prevents particles of undissolved sodium fluoride solids from infiltrating the solution area under the cone or within the pipe manifold. With the upflow type, no barrier is used, because the water comes up through the bed of sodium fluoride... 

The recommended maximum feed rates for downflow saturator at various water temperatures and sodium fluoride bed depths are listed in Table 9. At a given water temperature and bed depth, the water flow and solution feed rates are listed. The lower figures represent the maximum feed rate (or withdrawal rate) of saturated sodium fluoride solution and the upper figures represent the water flow rate which can be fluoridated to a level of 1.0 ppm of fluoride. These rates assume that there is less than... 

The upflow saturator provides a thicker bed of sodium fluoride and more fluoride-water solution, allowing for higher withdrawal rates than a downflow saturator. A maximum of 1000 mL/min saturated fluoride-water solution can be withdrawn from an upflow saturator this is a rate sufficient to treat about 5000 gpm of water to a fluoride level of 1.0 ppm. 

In the operation of a downflow-type saturator, water is introduced at the top of the saturator tank (there is an air gap to avoid the possibility of a cross-connection) and the level is regulated with a float-operated controller valve on the water supply line. The water then trickles down through the bed of sodium fluoride solids the solution is clarified in the sand and gravel filter bed and ends up as a clear, saturated solution at the bottom of the tank where it is withdrawn by the feeder. The fluoride-water solution pump withdraws the solution and delivers it into the water system at a desired dosage rate. Operator attention is required only to ensure that an adequate quantity of sodium fluoride solids is kept in the saturator and that the saturator is kept in a reasonably clean condition. 

Recommended Maximum Feed Rates for Downflow Sodium Fluoride Saturator (2)... 

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