2. BrineDraw/Slow Rinse Brine rinse is the forward flow regeneration of the resin bed using a saturated sodium chloride (NaCl) salt solution diluted to 30-38% saturation using an eductor system and fresh water. The diluted brine is eluted through the resin bed using a distributor inside the softener for even flow. The concentration of the salt through the resin bed should be above 30% saturation for a minimum of 30 minutes.

3. Rinse (fast)

The rinse sequence is forward flow and uses the city water or well water to flush out the remaining salt water. This rinsing also compacts and conditions the resin and helps to prevent channeling. Incorrect regeneration timing and improper flow rates are often the cause of problems in ion exchange softener systems. An elution study is used to collect process data during the regeneration and involves plotting the concentration (specific gravity) of salt during the brine draw cycle versus time. The information is then used to troubleshoot and evaluate the ion exchange process.

Elution study equipment 250 ml graduated cylinder – used for collecting brine rinse samples 1-100% Salometer – used for measuring percent saturation of the brine rinse samples Stopwatch or timer app – used for timing samples and the regeneration cycle

Elution study setup and sample collection points

Prior to the start of the study, check the concentrated brine tank with the salometer: the sodium chloride concentration should be 90% or higher. If the concentration is below 90%, the water has not had


Water Treatment

enough time to dissolve the salt or there is not enough salt in the brine tank. If necessary, add salt and wait until the concentration is above 90% prior to starting the study. Make certain to mark or measure the water level in the brine tank prior to start of regeneration. This can be used to calculate the volume of brine used during the process to compare and confirm the volume versus the manufacturers’ specification. Create a log sheet ahead of the procedure that records: time in minutes and percent saturation. For the actual study sampling, choose a sample point after the multiport valve on the discharge pipe prior to drain for the most accurate concentration measurements. Make certain there is enough flow during the brine rinse to fill a 250 ml cylinder in less than three minutes.

Elution study procedure

Determining the beginning of the brine draw can sometimes be difficult to determine based on the type of softener control. The brine rinse cycle, however, always follows the backwash and is typically indicated by a drop in the discharge flow rate. Softener flow controllers are either mechanical or digital. Mechanical controllers will typically have pins that indicate the cycle position, and digital controllers may have an LED display indicating the brine draw cycle. Once the brine draw cycle starts, the sampling procedure follows: 1. Sample the discharge water every three minutes by collecting the sample and placing the salometer in the cylinder. Allow the salometer to settle for a few seconds. 2. Take the reading from the salometer at eye level, record the time and the percent saturation on the log sheet. 3. Continue to collect samples at three-minute intervals, recording and logging the results.

Using more salt than necessary, reduce the brine draw flow rate.

Brine eductor draws too quickly check valve adjustment or replace dole valve.

Insufficient brine strength and contact time. Possible remedies are to increase brine draw time, decrease dilution water, and decrease slow rinse cycle time.

Issue 2 • March/April 2021

Brining cycle too short, interrupted by a premature rinse cycle. 57

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