Water softener abstract
A water softener and a method of operating the same are provided
to allow for the efficient use of either NaCl or KCl as the regenerant
salt. A user interface is provided to allow the user to indicate
to the computer controlling the water softener whether NaCl or KCl
is being used. The computer controller adjusts the fill time and
brine time, depending on the type of regenerant salt used and on
the temperature of the brine.
Water softener claims
1. In a water softener having a resin tank, a resin bed disposed
in the resin tank, and a brine tank intended to contain a salt for
regenerating the resin bed, the improvement comprising:
a. a brine feed-water adjustment means for filling the brine tank
with water during the regeneration cycle;
b. a temperature sensing means for determining the temperature
of the brine; and
c. the temperature sensing means being coupled with the brine feed-water
adjustment means, and the adjustment means adjusts the quantity
of water fed into the brine tank in accordance with the temperature
sensed by the temperature sensing means.
2. The water softener improvement of claim 1 wherein the temperature
sensing means is located in the brine tank.
3. The water softener improvement of claim 1 wherein the brine
feed-water adjustment means adjusts the quantity of water to be
substantially equal to the quotient resulting from the quantity
of salt desired for regeneration of the resin bed divided by the
solubility of the salt at the temperature of the brine.
4. The water softener improvement of claim 1 wherein the temperature
sensing means is located on a water source pipe which provides water
to the brine feed-water adjustment means.
5. A water softener, comprising:
a. a resin tank;
b. a resin bed disposed in said resin tank;
c. a brine tank for holding a quantity of regenerative salt and
for preparing a salt solution for regenerating the resin bed;
d. a piping system connecting said brine tank to said resin tank;
e. salt selection means for indicating a regenerative salt type
from a plurality of salt types;
f. water dispensing means for measuring and placing either a first
quantity of water in the brine tank when a first salt type is selected
or a second quantity of water in the brine tank when a second salt
type is selected, said second quantity of water being greater than
the first quantity of water; said water interacting with a salt
in the brine tank to form a brine;
g. means for connecting said brine tank to a source of water;
h. brine draw means for withdrawing brine from the brine tank and
running the brine to the resin tank and through the resin bed, whereby
the resin bed is washed with a first quantity of brine having a
volume substantially equal to the first quantity of water if the
first salt type is selected and a second quantity of brine having
a volume substantially equal to the second quantity of water if
the second salt type if selected; and
i. a temperature sensing means for determining the temperature
of the brine in the brine tank.
6. The water softener of claim 5 wherein the temperature sensing
means is located in the brine tank.
7. The water softener of claim 5 wherein the temperature sensing
means is on a source water pipe providing water to the water dispensing
8. The water softener of claim 5 wherein the temperature sensing
means is a sensor in the brine tank and which measures the temperature
of the brine, the sensor being connected to the water dispensing
means, whereby the water dispensing means adjusts the quantity of
water placed in the brine tank in accordance with both the salt
type selected and the temperature sensed by the sensor.
Water softener description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the art of water softening systems.
More particularly, the present invention is directed to a method
and apparatus for the efficient use of potassium chloride as the
regenerant in a water softener.
2. Description of Related Art
A number of different methods and systems are known in the art
for softening water. The water softening process involves the replacement
of "hard" ions, such as calcium and magnesium, with "soft"
ions such as sodium and potassium. Soft water is often desirable
because it is less likely to leave deposits on plumbing fixtures.
Water softeners typically utilize an ion exchange material, typically
present as a resin bed, to soften water. In the water softening
process untreated water is brought into contact with the resin bed
where "hard" ions are exchanged for "soft" ions
to provide a source of softened water. After prolonged contact with
untreated water, however, the capacity of the resin bed to soften
water becomes exhausted. When this occurs, the resin bed may be
regenerated by exposing it to a brine solution containing the desired
"soft" ions, which process restores its water softening
The brine needed for regeneration may be formed by dissolving in
a quantity of water a regenerant salt having the desired "soft"
ions. Typical regenerant salts are sodium chloride and potassium
chloride. The type of regenerant salt used determines what type
of "soft" ions will be present in the softened water.
In particular, sodium chloride results in sodium ions being introduced
into the softened water, and potassium chloride results in potassium
ions being introduced into the softened water.
Many water softeners regenerate the resin bed automatically. In
such systems the resin bed is in service most of the time softening
water. When the water softener system determines that regeneration
is required, it stops softening water and instead regenerates the
resin by exposing it to the brine. A number of different methods
are known for automatically determining when to initiate a regeneration.
Some of these methods are described in U.S. Pat. Nos. 5544072
and 4722797 which are incorporated herein by reference. Typically,
in such methods, regenerations are performed before the resin bed
is completely exhausted, in order to ensure that the user does not
run out of soft water.
In addition to determining when to regenerate, many systems automatically
select the amount of regenerant to be used in a regeneration step.
The regenerant is often provided in the form of dry regenerant salt
located in a vessel separate from the resin bed, termed the "brine
tank." A measured amount of water is introduced into the brine
tank in order to dissolve the desired amount of regenerant, forming
a brine. Typically, the rate at which water enters the brine tank,
the "fill rate," is fixed, so that the fill time determines
the amount of water introduced and therefore the amount of regenerant
salt dissolved. The brine is then transferred from the brine tank
to the resin bed, so that the resin bed is exposed to a known amount
of regenerant during the regeneration process. The used brine is
then disposed of as waste.
Sodium chloride (NaCl) has been the regenerant salt most commonly
used in water softeners. However, the use of potassium chloride
KCl) as the regenerant is an attractive alternative. The potassium
ions added to soft water from softeners regenerated with KCl are
more beneficial to human health as well as to plant life than the
sodium ions added to soft water from softeners regenerated with
NaCl. The use of KCl as the regenerant also often results in less
chloride being present in the waste brine, making its disposal less
Most water softeners, however, are designed for NaCl regenerant
and lack the flexibility to operate adequately if KCl is used as
the regenerant instead. In particular, if KCl is used as the regenerant,
the resin bed may become exhausted prematurely, i.e., before it
is regenerated. As a result, the user would run out of soft water.
The problem becomes more acute as a function of water temperature
and softener efficiency, i.e., the colder the water is that is used
to form the brine and the more efficiently the water softener uses
regenerant salt, the more likely premature exhaustion is.
Moreover, the use of KCl as the regenerant is more complicated
than the use of NaCl for a number of reasons. First, in certain
operational regimes, namely, when the resin bed is used most efficiently,
the resin bed requires a greater amount of KCl than NaCl for regeneration.
Second, the solubility of KCl in water is highly temperature dependent,
unlike NaCl. In particular, the solubility of KCl in cold water
is greatly reduced relative to NaCl. As a result, when cold water
is used to form the brine, a greater amount of water is required
to dissolve the KCl. Third, the dissolution of KCl in water is significantly
endothermic, so that the KCl cools the water as it dissolves, thereby
lowering its solubility even more. Finally, KCl dissolves in water
at a slower rate than NaCl.
U.S. Pat. Nos. 5544072 and 4722797 each disclose a method and
apparatus for operating a water softener. These references also
disclose that either potassium chloride or sodium chloride may be
used as the regenerant, but they do not suggest any changes to the
water softening method or apparatus depending on whether NaCl or
KCl is used. Such changes are required, however, because of the
different characteristics of these two salt types. As a practical
matter, then, water softeners in accordance with these references
do not have the flexibility to be able to use either NaCl or KCl
at the option of the user. Moreover, these references do not disclose
any way of accounting for the more complicated characteristics of
KCl, such as its temperature dependent solubility, in order to use
KCl as a regenerant in an efficient and reliable manner.
SUMMARY OF THE INVENTION
The principal object of the present invention is to provide a water
softener and a method of operating the same to allow for the efficient
and reliable use of KCl as the regenerant salt.
Another object of the present invention is to provide a water softener
method and apparatus having the flexibility to allow either NaCl
or KCl to be used as the regenerant salt at option of the user.
Yet another object of the present invention is to provide a method
and apparatus for filling the brine tank of a water softener to
account for changes in the brine temperature occurring during the
course of the fill and thereby to ensure that the required amount
of regenerant salt is dissolved.
In accordance with the present invention, a water softener and
a method of operating the same are provided to allow for the efficient
and reliable use of either NaCl or KCl as the regenerant salt. A
user interface is provided to allow the user to indicate to the
computer controlling the water softener whether NaCl or KCl is being
used. The computer controller adjusts the fill time and brine time
depending on the type of regenerant salt used. The temperature of
the brine is measured at regular intervals as water is being supplied
to the brine tank to dissolve the KCl. At each interval the computer
calculates the amount of water needed to dissolve the required amount
of KCl, and the fill ends when the amount of water added is approximately
equal to the required amount calculated at the most recent time
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a graph which illustrates curves representing the capacity
of a typical resin bed as a function of the salt dosage used to
regenerate it. The solid line corresponds to the use of NaCl as
the regenerant, and the dotted line corresponds to the use of KCl.
FIG. 2 is a schematic representation of an automatic water softener
in accordance with the present invention.
FIG. 3 is a schematic representation of a user interface for the
water softener in accordance with the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Water hardness is typically expressed in terms of grains per gallon,
which represents the weight in grains of calcium carbonate (CaCO.sub.3)
which would be needed to be dissolved in one gallon of water to
achieve that level of hardness. The capacity of a resin bed, which
represents the amount of water of a given hardness it can soften
before becoming exhausted, is therefore expressed in grains as follows:
where C=capacity of the resin bed in grains, H=the hardness of
the water in grains per gallon, and V=the amount of water in gallons
at that hardness that can be treated by the resin bed before exhausting
When the resin bed becomes exhausted, it may be regenerated by
exposing it to a brine comprising a quantity of regenerant salt
dissolved in water. The salt dosage, dissolved in water as a brine,
required to regain the desired capacity depends on the efficiency
of the resin bed. The efficiency, E, of a resin bed is defined as
where D=the dosage of regenerant salt applied to the resin bed
in pounds, and C=the capacity of the resin in grains resulting from
that salt dosage.
The water softening process, to the extent that it involves the
removal of calcium ions, involves the exchange of either two Na.sup.+
ions or two K.sup.+ ions for one Ca.sup.2+ ion. Since the molecular
weights of CaCO.sub.3 KCl, and NaCl are 100.09 74.56 and 58.44
respectively, and since 1 pound=7000 grains, the theoretical efficiency
is 5995 grains/lb. when NaCl is used and 4699 grains/lb. when KCl
is used. Theory thus predicts that NaCl is 28% more efficient as
a regenerant salt than KCl, with the result that more KCl would
be required for regeneration in order to achieve the same capacity.
In practice, however, resin beds approach their theoretical efficiencies
only when low salt dosages are used. The reason for this is that
the capacity cannot be increased without limit by increasing the
salt dosage. With higher salt dosages, the resulting capacity levels
off and gradually approaches a limiting value. Put another way,
as the salt dosage is increased, the efficiency falls increasingly
below its theoretical value. Moreover, it has been found that for
sufficiently high salt dosages, the amount of NaCl and KCl needed
to achieve the same capacity becomes essentially the same.
This general trend is illustrated schematically in FIG. 1 which
is a graph of the capacity of a typical resin bed in grains as a
function of NaCl and KCl dosage in pounds. The NaCl curve is a solid
line, and the KCl curve is a dotted line. As shown in that graph,
when low salt dosages are used, NaCl results in a greater capacity
than the same dosage of KCl. However, with higher salt dosages the
resulting capacity becomes nearly independent of the type of salt
Many water softeners operate in the regime where NaCl and KCl have
nearly the same efficiency. However, a more efficient use of regenerant
salt is obtained by using lower salt dosages, albeit at the cost
of more frequent regeneration. In this regime, then, the lower efficiency
of KCl, as compared to NaCl, must be compensated for by increasing
the KCl dosage during regeneration.
Preferably, curves for KCl and NaCl like those in FIG. 1 are generated
for each resin bed to determine the salt dosage required to achieve
the desired capacities. Such data is typically obtained by exhausting
the resin bed until the effluent water has a hardness of one grain
per gallon. The resin bed is then regenerated with a regenerant
brine having a selected salt dosage. Water of a known hardness is
passed through the resin bed until the effluent water reaches a
hardness of one grain per gallon. The amount of water that has passed
through the resin bed is measured, and from this quantity the capacity
of the resin bed may be calculated. This procedure is then repeated
for various salt dosages to generate the curve of capacity versus
salt dosage as in FIG. 1.
An automatic water softener 10 adapted to use potassium chloride
in accordance with the present invention is shown schematically
in FIG. 2. When water softener 10 is "in service" it is
designed to treat hard water to provide a source of soft water.
Periodically, water softener 10 automatically goes out of service,
thereby ceasing the softening of water, and enters a "regeneration
cycle" designed to regenerate its capability to soften water.
With reference to FIG. 2 water softener 10 preferably includes
a source pipe 12 connected to a source of hard water 14 a destination
pipe 16 connected to a destination 18 intended to use the softened
water, and a drain pipe 20 connected to a drain 22. Pipes 12 16
and 20 are also connected to a control valve 24. A resin bed 26
preferably comprising particles of ion exchange resin, is disposed
in a resin tank 28. A pipe 30 and a pipe 32 connect resin tank 28
to control valve 24. A brine tank 34 holds a quantity of a regenerant
salt 36 typically NaCl or KCl, and is connected to an aspirator
valve 38 by a pipe 40. Pipe 40 includes a brine valve 42. Pipes
44 and 46 connect aspirator valve 38 to control valve 24. Control
valve 24 may be configured to interconnect pipes 12 16 20 30
32 44 and 46 in a number of different ways hereinafter described.
Water softener 10 preferably includes a micro computer controller
48 having a user interface 50. User interface 50 shown schematically
in FIG. 3 preferably includes an LCD display 60 and various buttons,
such as a "SELECT" button 62 an "UP" button
64 and a "DOWN" button 66 to allow the user to selectively
view and enter in information. A timer 52 is provided to enable
controller 48 to measure time durations. A water meter 54 is placed
in either pipe 30 or pipe 32 to enable controller 48 to measure
the amount of water flowing through resin tank 28. A temperature
sensor 56 is preferably disposed in brine tank 34 to enable controller
48 to measure the temperature therein. Temperature sensor 56 is
preferably a thermocouple or a semiconductor device. Controller
48 sets the configuration of control valve 24.
When in service, hard water from source 14 passes through supply
pipe 12 to control valve 24 which is configured so that the hard
water then flows through pipe 30 to resin tank 28. In resin tank
28 the hard water passes through resin bed 26 where it is softened
by an ion exchange process. The soft water flows out from resin
tank 28 through pipe 32 to control valve 24. Control valve 24 is
configured to direct the soft water from pipe 32 to pipe 16 where
it is directed to its destination 18.
When the resin bed 26 loses its capacity to effectively soften
the water passing through it, regeneration is necessary. The regeneration
cycle preferably includes the following steps: (1) fill; (2) brine
draw; (3) slow rinse; (4) backwash; and (5) fast rinse. During the
fill step, a quantity of water flows into brine tank 34 to dissolve
a quantity of the salt 36 therein in order to make the amount of
brine necessary for regeneration. Specifically, control valve 24
is configured so that hard water from source 14 flows through pipe
12 to pipe 30 to resin tank 28. The hard water passes through resin
bed 26 and flows out through pipe 32 to control valve 24. Control
valve 24 is configured to direct this water to pipe 44 and then
to pipe 40 through aspirator valve 38. Brine valve 42 opens in response
to the flow of water in pipe 40 allowing the water to enter brine
tank 34. The water filling brine tank 34 dissolves a quantity of
the salt 36 to form a brine. Temperature sensor 56 preferably measures
the temperatures of the water and of the resulting brine. The duration
of the fill step determines the amount of water that enters brine
tank 34 and therefore the amount of regenerant salt dissolved and
available for regeneration.
During the brine draw step, control valve 24 is configured so that
hard water from pipe 12 is directed to pipe 44 whereupon it flows
through aspirator valve 38 to pipe 46. This flow through aspirator
valve 38 creates suction on pipe 40 by the Venturi effect. Brine
valve 42 is open, so that the suction on pipe 40 draws the brine
in brine tank 34 formed during the fill step, up into pipe 40 which
then flows through aspirator valve 38 to pipe 46. Control valve
24 is configured so that the water and brine from pipe 46 are directed
through pipe 30 to resin tank 28. The brine entering resin tank
28 flows through resin bed 26 thereby regenerating it, and flows
out through pipe 32 as waste. The waste is directed to drain 22
via pipe 20 for its disposal. The duration of the brine draw step
is sufficiently long so as to withdraw all or nearly all of the
brine from brine tank 34. Preferably, brine valve 42 closes automatically
when the level of brine in brine tank 34 falls below a prescribed
During the slow rinse step, brine valve 42 is closed, and brine
is no longer withdrawn from brine tank 34. However, water keeps
flowing as in the brine draw step. In particular, the configuration
of control valve 24 is the same as for the brine draw step. The
remaining brine continues to flow through resin bed 26 until replaced
with incoming water in order to achieve maximum ion exchange and
to continue to flush out any hardness minerals or brine which may
remain in resin tank 28.
During the backwash and fast rinse steps, control valve 24 is configured
so that hard water from pipe 12 is directed so that the water flows
through the resin bed and is directed to drain 22 via pipe 20. During
the backwash step, the water flows up through resin bed 26 lifting
up and expanding the resin bed 26 and flushing out iron minerals,
dirt, sediments, hardness minerals, and any remaining brine. During
the fast rinse step, a fast flow of water is directed downward through
resin bed 26 to pack it and prepare it for service.
Controller 48 determines when to regenerate resin bed 26 and to
what capacity. Various methods may be used for these determinations,
such as those described in U.S. Pat. Nos. 5544072 and 4722797.
The necessary capacity will, in general, depend on the hardness
of the water to be treated. User interface 50 therefore preferably
includes means by which the user can enter the water hardness, expressed
in grains per gallon, into controller 48. To accommodate the use
of different types of regenerant salt, user interface 50 also enables
the user to specify the type of salt used, e.g., whether NaCl or
KCl is used.
Preferably, the user-adjustable parameters, which typically include
the time of day for regeneration, the water hardness, and the type
of regenerant salt used, are shown as various "screens"
on display 60 with each parameter having its own screen. At each
screen, the user is able to scroll up and down through the available
values for the parameter by pressing "UP" button 64 and
"DOWN" button 66 respectively. The user indicates the
desired value for the parameter by pressing "SELECT" button
62 whereupon the value is stored by computer controller 48 and
the next "screen" is shown on display 60. In this way,
the user is able to scroll through the available salt types, such
as NaCl and KCl, and to make a selection. Other means for indicating
the regenerant salt type, such as other types of computer interfaces
or mechanical switches, could also be used.
From the desired capacity to which resin bed 26 is to be regenerated,
the required salt dose may be determined from empirical data as
described above. The salt dosages, D, for each desired regenerated
capacity, C, are programmed into controller 48 for the various salt
types intended to be used, such as NaCl and KCl. Thus, from the
type of salt used and the regenerated capacity required, controller
48 is able to determine the salt dosage, D, needed for regeneration.
The value of D, the salt dosage, determines the amount of water
that must be supplied to brine tank 34 during the fill step, based
on the solubility of that salt. Preferably, the amount of water
added during the fill step is determined by the fill time, the flow
rate being a fixed quantity. The required fill time may thus be
calculated as follows:
where F=fill time in minutes, D=the salt dosage in pounds, R=the
fill rate in gallons per minute, and S=the solubility of the salt
in pounds per gallon. When KCl is used as the regenerant salt, however,
an added complication arises in that its solubility is markedly
temperature dependent over the typical range of water temperatures
encountered, namely, 34.degree. F. to 80.degree. F., whereas the
solubility of NaCl is relatively constant over this range. In particular,
the solubilities of NaCl and KCl are both approximately 2.99 lbs./gal.
at 80.degree. F. At lower temperatures, the solubility of KCl is
significantly less than that of NaCl as summarized in Table 1. The
information in Table 1 has been generated from empirical data linearized
in the range of 34.degree. F. to 80.degree. F., with the solubility
of NaCl taken to be a constant 2.99 lbs./gal. The data of Table
1 is representative only, in that results can be affected by the
water chemistry in the particular application.
TABLE 1 Temp. KCl Solubility KCl/NaCl Difference (.degree. F.)
(lbs./gal.) (%) 34 2.35 27.2% 36 2.38 25.7% 38 2.40 24.2% 40 2.43
22.8% 42 2.46 21.4% 44 2.49 20.1% 46 2.51 18.8% 48 2.54 17.5% 50
2.57 16.2% 52 2.60 14.9% 54 2.63 13.7% 56 2.65 12.5% 58 2.68 11.4%
60 2.71 10.2% 62 2.74 9.1% 64 2.76 8.0% 66 2.79 6.9% 68 2.82 5.9%
70 2.85 4.9% 72 2.88 3.8% 74 2.90 2.8% 76 2.93 1.9% 78 2.96 0.9%
80 2.99 0.0%
To accommodate the use of KCl, the fill times should be adjusted
on the basis of water temperature to reflect the temperature dependent
solubility of KCl. The simplest approach to account for this effect
is not to measure the actual water temperature at all but to simply
assume a typical water temperature and to increase accordingly the
fill time for KCl by a fixed percentage relative to the fill time
that would be required if NaCl were used. An increase in the fill
time of 25% is found to be a reasonably adequate approximation for
the most typical water temperatures encountered.
A more accurate system includes temperature sensor 56 in order
to enable controller 48 to determine the temperature of the water
being supplied to brine tank 34. Temperature sensor 56 is preferably
located in brine tank 34 but may alternatively be located upstream,
such as in source pipe 14. Controller 48 is programmed with the
solubilities of KCl at various water temperatures, so that when
KCl is used as the regenerant salt controller 48 measures the water
temperature and sets the required fill time accordingly.
Alternatively, the water temperature may be a user-adjustable parameter
entered into computer controller 48 by means of user interface 50
as previously described.
The temperature of the brine formed in brine tank 34 does not remain
constant during the course of the fill. An example of how the brine
temperature changes during the course of a fill when KCl is used
as the regenerant salt is shown in tabular form in Table 2. This
temperature changed is caused by two factors. First, before the
fill begins, the temperatures of the water and of brine tank 34
with dry regenerant salt 36 present within will not in general be
equal, so that the brine temperature will naturally equilibrate
during the course of the fill. Second, the dissolution process of
the salt also changes the temperature of the brine. In particular,
the dissolution of KCl is significantly endothermic, so that the
dissolution process itself cools the brine.
The temperature change of the brine during the course of the fill
thus presents an added difficulty in the case of KCl because of
its temperature dependent solubility. Temperature sensor 56 should
thus measure the temperature during the course of the fill, preferably
at regular intervals such as every minute. Typical results under
this method are tabulated in Table 2.
TABLE 2 Required Sample Fill Required Fill Time Temp Solubility
Water Fill Time (Min) (.degree. F.) (lbs/gal) (gal) (min) 0 60 2.7048
2.219 7.40 1 56 2.6492 2.265 7.55 2 52 2.5937 2.3133 7.71 3 48 2.5381
2.3640 7.88 4 46 2.5103 2.3902 7.97 5 44 2.4826 2.4168 8.06 6 42
2.4548 2.4442 8.15 7 41 2.4409 2.4581 8.19 8 40 2.4270 2.4722 8.24
8.24 -- END OF FILL --
The preferred method of using KCl as the regenerant is described
as follows. At regular time intervals during the fill, the temperature
at temperature sensor 56 is measured. From this temperature, the
solubility of the salt is calculated, and from this value the required
volume of fill water and ultimately the required fill time may be
calculated, as shown in Table 2. The fill then proceeds until the
required fill time is approximately equal to the actual fill time.
Even after the fill ends, the brine temperature is often observed
to continue to drop when KCl is used. This may be due to the dissolution
rate of KCl which is less than that of NaCl. In other words, the
KCl continues to dissolve even after the flow of water stops, thereby
cooling the brine even further. The temperature drop is observed
to be fairly small--typically 2.degree. F. The temperature drop
reduces the solubility of KCl even further, so that less dissolved
KCl is present in the brine as result. The way to compensate for
this effect is to add more water during the fill step by increasing
the fill time. Typically, a 1% increase in the fill time is all
that is required.
When the fill time is adjusted, the brine draw time must also be
adjusted to ensure that the required amount of brine is withdrawn
from brine tank 34. Typically, the ratio of the brine draw time
to the fill time is a fixed quantity, so that the brine draw time
may be taken to be the fill time multiplied by this quantity. The
slow rinse time is typically fixed. Preferably, controller 48 calculates
the necessary brine draw time based on the fill time actually used.
The total "brine time" is then the sum of this necessary
brine time and the slow rinse time. Controller 48 maintains control
valve 24 in the brine draw/slow rinse configuration for this "brine
time" to ensure that the required amount of brine is withdrawn.
In the case where the fill time for KCl is increased by 25% relative
to NaCl, a corresponding increase in the "brine time"
for KCl of approximately 12.5% relative to NaCl is found to be sufficient.
The above described embodiments are merely illustrative of the
features and advantages of the present invention. Other arrangements
and advantages may be devised by those skilled in the art without
departing from the spirit and scope of the present invention. Accordingly,
the invention should not be deemed to be limited to the above detailed
description but only by the claims that follow.