UFC 3-240-13FN
25 May 2005
sodium and hardness brine from the bed. The volume of fresh water is equal to 1000 to
3000 liters per cubic meter (7.5 to 22.5 gallons per cubic foot) of bed volume.
2-2.5.1.2.4 Fast Rinse. In the last step, a fast rinse is used, also with downflow, to
remove any traces of the sodium and hardness brines. This is done at a rate of 200 to
270 liters per minute per cubic meter (1.5 to 2 gallons per minute per cubic foot) of bed
volume until the discharge is free of hardness; 4690 to 13,400 liters per cubic meter (35
to 100 gallons per cubic foot) of bed volume is required. The unit is now ready for
another service cycle.
2-2.5.1.3
Testing and Record Keeping. Influent water should be tested for
hardness on a weekly basis. The softener effluent water should be tested for hardness
on a daily basis, every shift (3 times a day), or as required for systems that require
frequent (1 to 3 days) or less frequent regeneration. Accurate records should be kept of
these tests, including recording the number of liters (gallons) of water that have been
treated during each service cycle, and the amount of salt that was used during each
regeneration cycle.
2-2.5.1.4
Operating Problems. Several common problems are sometimes
encountered during softener operation:
2-2.5.1.4.1 Resin Fouling. A normal decrease in exchange capacity due to resin
fouling is about 5% per year. Any decrease greater than this should be investigated and
the reason determined.
2-2.5.1.4.2 Fouling Due to Iron. A common cause of loss of capacity is resin fouling
by iron salts. Soluble iron will exchange for sodium during the service cycle, but sodium
will only be incompletely exchanged for iron during the regeneration cycle. There is a
simple test to determine iron fouling: a pinch of iron-fouled ion exchange material added
to a 10% hydrochloric acid solution in a test tube will cause the hydrochloric acid to turn
yellow, indicating the presence of iron.
Iron-fouled resin can be returned to design capacity by cleaning with dilute
hydrochloric acid, sodium bisulfite, or special resin cleaners. Specific procedures are
required.
NOTE: The softener manufacturer's recommendations should be consulted before
using this acid cleaning procedure, including those prohibiting acid procedures with a
galvanized or unlined steel tank. To use acid procedures, the tank must be constructed
of reinforced plastic or rubber, or must be plastic-lined with no breaks in the lining.
2-2.5.1.4.3 Improper Backwash. Improper backwash is another common problem. A
backwash rate that is too high can result in the ion exchange material being washed out
of the unit. The bed depth can be measured by carefully probing to the underdrain
support bed. Normal bed depth is usually 0.75 to 1 meter (30 to 36 inches). The bed
volume in cubic meters (cubic feet) can be calculated by the following formula:
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