How is the Softening Process Controlled?
The key to practical and
economic operation of a water softener is proper utilization of the resin. The resin must be regenerated before it
is exhausted. If not, the product
water will be hard. The resin capacity
must be nearly exhausted otherwise, salt and rinse water will be wasted. This
balance, between the continuous production of soft water and the necessity of
fully utilizing the resin on every run, controls the frequency of
regeneration. The interval between regenerations should be controlled to
prevent hard water from passing the unit and still gain maximum capacity from
setting the softener conserves water and salt. Every regeneration cycle
requires a preset amount of salt. If the bed is not near exhaustion salt will
be applied to the bed and no exchange will take place. Every regeneration
uses a preset amount of water for backwash, brining, and rinsing. As the frequency of regeneration is
increased, the wastewater as a fraction of produced water increases.
uses salt and water, which become waste products. Brine wastes produced by a water softener can increase the
total dissolved solids of streams causing regulatory problems for industry. Water is a precious and expensive
commodity, which should be conserved. Proper setting of the regeneration
frequency reduces the discharge of salt into the environment and conserves
commercial - industrial applications, softeners are used to protect equipment
from scaling and calcining. They are
frequently used to treat water for boilers, reverse osmosis units, ice
machines, and other industrial process uses.
Do not be so zealous in conserving water and salt that you produce
hard water, which damages expensive equipment.
refers to systems that require an operator to throw a switch, push a button,
or turn a valve to initiate the regeneration cycle. If the operator has the time to pay careful attention to the
produced water hardness and volume, this can be the most efficient method.
Control Scheme. The operator
should regularly monitor the produced water hardness and volume. Before the hardness starts to increase,
the softener should be regenerated.
By keeping consistent records, the operator can become an expert at
predicting the optimal time between regenerations. Manual initiation of the
cycle allows the operator to avoid regeneration during peak water use times
in the plant. It also allows
flexibility of operation. The
disadvantage is the time and energy required of the operator. Manually initiated regeneration is best applied
when continuous operator attention is available, raw water demand and
hardness are variable, and water quality is critical. It should also be noted that all of the
"automatic" regeneration systems allow for manual initiation of the
regeneration cycle. Manual controls
are often the least expensive and most cost effective option.
Time Clock Control
regeneration is initiated with a timer it is called “timer controlled”. If
usage and hardness are consistent, a constant time interval between
regenerations provides effective use of the resin.
Softeners can be equipped with a time clock that
initiates the regeneration cycle at specific time intervals. This allows the operator to choose a recurring preset
time of regeneration. The time
interval between regenerations must be chosen so that the resin does not
become completely exhausted and produces hard water. If water usage and hardness are constant,
then time clock regeneration can be efficient. Variable demand can be troublesome to time clock initiation
since high demand periods may exhaust the resin before it is due for
regeneration. Low demand periods can
cause premature regeneration resulting in partial use of the resin, which
wastes salt and water. The main
advantage of time clock regeneration is that the operator does not have to be
present to initiate regeneration.
Control Scheme. When setting the softener controls based on time, the time
interval between regenerations will be related to resin capacity, resin
volume, water hardness, and flow. The
following equation applies:
Interval Between Regenerations = 90% x (Resin Capacity x Resin Volume) /
(Hardness x Average Flow per Day)
The time clock on
the softener is set for a time equal to or less than the calculated time
interval between regenerations. The
resin capacity is based on the salt used for regeneration. The raw water hardness and flow must be
assumed and will be different for each installation. Since the resin capacity and volume are
constant, the time interval between regenerations is dependent on the
hardness and flow. If either vary
significantly, the preset interval between regenerations may be
inefficient. In many situations, the
hardness and flow are quite consistent and time clock regeneration is ideal. Usually regenerations are scheduled in
the early morning hours when water usage is at a minimum.
Time Clock versus Manual
clock initiated regeneration is usually more expensive than manual
regeneration because the valves must be automated. This requires solenoid activated diaphragm valves or a five
cycle softening valve. Time clock
regeneration works well if the flow and hardness is relatively constant. If
the flow increases over normal levels, it is possible to exhaust the resin thereby
passing hard water. If the water
usage is lower than normal, the time clocks will initiate regeneration well
before the resin is exhausted. This
premature regeneration will waste salt and rinse water. These objections can be overcome by
attention to flow rates and appropriate adjustments. The time clock system is rugged and
Electronic Timers. Current practice is to use electronic timers that are capable of tracking
both the time of day and the time of each of the softener cycles. These
electronic devices provide contact closures at certain preprogrammed times of
the day to initiate regeneration. Once initiated the timer controls the time
of each of the five regeneration cycles. The Water King ERCt is an example of
an electronic timer. (1)
totalizing flow meter can be added to a softener control system to regenerate
based on the total volume of treated water.
Demand regeneration initiates a regeneration cycle when the totalized
flow applied to the bed reaches a preset quantity. The totalizing flow meter is reset after every regeneration. When the flow past the meter has
accumulated to the set point, the flow meter initiates regeneration.
Control Scheme. A demand regeneration system consists of a flow meter, a
totalizer, a preset volume, and an automated valve system. When the hardness
is constant, the quantity of water required to exhaust the resin capacity
will remain constant. Regenerating
based on demand can be an exact method of control. It protects against totally expending the resin in times of
high use and allows for longer runs if the flows are low.
setting the softener controls based on totalized flow or demand, the volume
setting on the flow monitor is based on the resin capacity, resin volume, and
raw water hardness. The following
or Totalized Flow Set Point = 90 % x (Resin Capacity x Resin Volume) /
has been mentioned that the capacity and resin volume are usually
constant. If the hardness is also
constant, which is often the case, the equation shows that the totalized flow
must also be constant.
Demand versus Time Clock or Manual Control. The demand regeneration system is more
expensive than timers or manual systems due to the extra cost of the meters
and another layer of electronic controls. For most applications, the savings
in salt and rinse water costs will justify the additional capital. If the
flow rates are relatively constant the added efficiency of demand
regeneration over time clock regeneration may be minimal. As compared to time
clock control, demand initiation eliminates flow as a variable in the
equation and decreases the chance for the release of untreated water.
based regeneration can be a problem if the preset volume is reached in the
middle of the day. Taking a softener
out of service during a peak usage time is often unacceptable. Using twin alternating units can solve the
problem of regeneration at inconvenient times of the day. One unit is in
service while its twin is in regeneration or standby. Each unit is sized to
treat the entire flow. In this way, a constant stream of softened water is
demand controllers have a built in algorithm to predict the remaining volume
that can be treated prior to regeneration and to anticipate the volume of
water to be treated. A fixed time window (usually during off peak hours) is
set for regeneration. If the algorithm predicts that the unit will be exhausted,
it regenerates prior to reaching the set point. This avoids regeneration
during peak demand periods. The Water King ERCd has such an algorithm called
the variable reserve function.
Systems. All of the Water King Series (BF LT, MF,
and VN) can operate in demand regeneration mode. These systems must have a
meter to measure the flow of soft water from the unit. The meter is placed in
the service line (outlet line) of the softener. The pulse must be counted and then converted into a flow
measurement and then totalized. This is accomplished by the demand controller.
The valve sequencing can be accomplished by the demand controller, or it can
be done by a cycle timer at the valve. Finally, the valve or valves must be
positioned to create the five cycles of softening.
(1) Electromechanical Timers. Prior to about 2000, water softener and filter valves are commonly
equipped with electromechanical timers. The timers track the day, time of
day, and also include a cycle timer. The latter is a separate dial, which
sets the time of the cycles of regeneration.
The timer has a clock with a time of day wheel and a day of the week
wheel. It allows every day, every other day, every three days, every four
days, every six days, or every twelve days. Seven-day timers are also
available. They can be set to regenerate at a single time of the day on any
day of the week. For example, a seven-day timer could be set to regenerate
every Tuesday, Thursday, and Saturday at 2:00 am. If Sunday were a day off,
the regeneration frequency would conveniently be every two working days.
A special type of timer
is used in demand regeneration systems.
These are simple cycle timers with no time of day or day clocks. They are designed to initiate and control
the regeneration sequence when they receive a pulse of control voltage
(usually one to three minutes). The
control voltage pulse is sent from a demand controller such as the EDR IIä . The ARC
timer is an example of a cycle timer used in demand regeneration systems on
the now discontinued brass Task Masterä valves.