1. c. Adequate contact of the water with the cation-exchange material is probably the most important requisite in successful cation-exchange water softening. This contact is influenced by factors such as hardness of water, depth of media, rate of flow, distribution of water and regenerant flow and character of the exchanger.
2. True. To secure maximum contact of water with resin ion-exchange sites, reasonably clear water must be applied to the exchanger to avoid coating of its particles with colloidal or suspended matter from the water.
4. False. Only to a slight degree will the iron, manganese and aluminum be removed from a cation exchanger during regeneration with salt brine. Since these ions will readily form insoluble hydroxides on a shift in pH or in contact with dissolved oxygen, a large percentage of the exchanged ions will precipitate within the ion-exchange resin bead and often becomes mechanically locked within the structure. There is some removal of iron, manganese and aluminum from the resin during regeneration, but it may only be a reaction at or near the surfaces of the beads. Resins handling heavy concentrations of iron, for example, may become so contaminated that the exchange capacity for softening can be reduced below the economic level.
5. a. Modern water softener valves pull concentrated brine (26 percent NaCl) from the brine tank via venturi-action water eductors. The eductor water serves not only as the motive force to suck out the brine, but also as a diluent to bring the brine to the proper 10 to 15 percent NaCl concentration.
6. c. After the brine eductor has delivered the proper quantity of brine (pounds of salt) to the resin bed for regeneration, this brine must be forced on through the ion exchanger to complete the contact time necessary for an efficient and economical regeneration, and also it must be removed from the resin before the unit is returned to service. Slow rinse water is applied over the head of the resin bed at the same flow rate and in the same manner as the brine is applied. Because of its greater density, the brine moves on down through the resin bed in a piston fashion. After the optimum concentration of brine has passed from the unit, the rinse rate is increased approximately fivefold to completely remove the last traces of chloride more quickly.
7. False. The first one-third of the spent brine that comes from resin bed regeneration contains approximately 80 percent of the hardness. The second one-third of the brine is high in sodium and contains the remainder of the hardness being removed. The last one-third portion contains the last traces of salt washed from the bed. The salt content of the middle one-third portion is generally high enough that it can be used in subsequent regeneration, or it may be used to backwash the exchanger, or it may be used initially in a regeneration followed by sufficient fresh brine to obtain the desired capacity.
8. False. The most important factor in determining the exchange capacity of a water softener is the amount of salt used in the regeneration. Higher pounds of salt per cubic foot of exchanger resin or mineral zeolite yield higher total grains of hardness exchange capacity per cubic foot. Low dosages of salt, on the other hand, results in the most efficient utilization of the regenerant (i.e., the greatest grains of hardness exchange per pound of salt used). At 15 lbs. of salt per cubic foot of resin over 30,000 grains capacity but only about 2,000 grains per lb. of salt can be achieved. At 5 lbs. of salt per cubic foot of resin, on the other hand, less than 20,000 grains capacity but almost 4,000 grains per lb. of salt is attained.
9. True. To go much below 5 lbs. of salt per cubic foot of resin may invite erratic operation of a water softener. At low salt dosages the quantity of brine involved in the regeneration may become so small that to obtain the contact time essential, the flow rate drops to the point where there is not enough back pressure created in the bed to evenly distribute the flow and to prevent streamlined channeling or short circuiting of the bed.
10. False. Since ion-exchange occurs so rapidly in resins, the operating capacities of softener units are little affected by increasing service flow rates up to as high as 15 or more gallons per minute. Performances are not significantly impacted when intermittent flow rates in domestic water softeners may rise to the maximum hydraulic capacity of the unit for short periods, provided this is followed by a period of inactivity in which the resin can recover.