Water softener abstract
Detection of exhaustion of sodium form water softeners is accomplished
by subjecting sample of the outflow from a water softener to reverse
osmosis in order to separate monovalent (sodium) and divalent (hardness
or magnesium and calcium) ions differentially from the outflow and
measuring conductivity before and after the reverse osmosis. The
two conductivities are compared in a ratiometer or differential
device. After the softener becomes exhausted the divalent ion concentration
in the outflow increases. Consequently the conductivity ratio changes
to indicate that the water softener has become exhausted.
Water softener claims
What is claimed is:
1. A method of determining the relative exhaustion of a sodium
form water softener which comprises the steps of:
measuring the conductivity of a sample of the outflow of the water
removing sodium and hardness ions from the sample at different
rates downstream of said measuring;
measuring the conductivity of the sample downstream of said removal;
determining the ratio of said measurements; and
determining said relative exhaustion from changes in said ratio.
2. The method of claim 1 including the step of:
applying forces proportional to said measurements to an indicating
device to indicate said relative exhaustion.
3. The method of claim 1 for indicating breakthrough of the water
softener including the step of:
indicating breakthrough when the change in said ratio of measurements
exceeds a predetermined threshold level.
4. The method of claim 1 including the step of:
taking the sample of water to be measured upstream of the output
of the water softener, whereby total exhaustion of the water softener
may be anticipated.
5. The method of claim 4 for continuously operating a water softener
in a nonexhausted condition, including the additional steps of:
applying forces proportional to said measurements to a switching
device to maintain the switch in a first state during normal operation
of the water softener, said forces causing the switch to change
to a second state when the ratio of said measurements changes more
than a predetermined threshold amount indicating anticipated breakthrough;
causing regeneration of the water softener to begin upon change
to said second state;
maintaining regeneration for a predetermined time period thereafter.
6. The method of claim 1 wherein the difference in said removal
rates is in the order of 10 to 1.
7. The method of claim 6 wherein the sodium ions and hardness ions
are removed at the rates of approximately 90% and 99% respectively.
8. The method of claim 1 wherein the sodium and hardness ions are
removed from the sample by applying the sample to a membrane exhibiting
9. The method of claim 8 wherein said differential rejection is
accomplished by reverse osmosis.
10. Apparatus for determining the relative exhaustion of a sodium
form water softener having a tank including ion exchange material
in the flow path of the water to be softened, comprising:
a first flow-through cell for measuring the conductivity of water
flowing therethrough connected to the tank to receive a sample of
the water therein that has contacted the ion exchange material;
means connected to the downstream side of the first cell for removing
sodium and hardness ions from the sample flowing therethrough at
a second flow-through cell for measuring the conductivity of water
flowing therein connected to the downstream side of the ion removing
signal processing means connected to both conductivity cells to
determine the relative exhaustion of the water softener by detecting
changes in the ratio of the conductivities measured.
11. The apparatus of claim 10 wherein the signal processing means
a member mounted for motion;
means connected to the first cell for applying a force to the member
proportional to the conductivity measured by said first cell;
means connected to the second cell to apply a counterbalancing
force to the member proportional to the conductivity measured by
said second cell; and
means for determining the relative exhaustion of the water softener
as a function of the position of the movable member.
12. The apparatus of claim 10 for indicating breakthrough of the
water softener wherein the signal processing means includes:
means connected to the cells to detect any change in the ratio
of the measurements exceeding a predetermined threshold level.
13. The apparatus of claim 10 wherein the first flow cell is connected
to the tank upstream of the outlet thereof whereby total exhaustion
may be anticipated.
14. The apparatus of claim 13 wherein the signal processing means
a member mounted for motion;
means connected to the first cell to apply a force to the member
proportional to the conductivity measured by the first cell;
means connected to the second cell to apply a counterbalancing
force to the member proportional to the conductivity measured by
the second cell, said forces being balanced to maintain the member
in a first state until a change in the ratio of the measurements
exceeds a predetermined threshold level whereupon said forces maintain
the member in a second state; and
means connected to the member to cause regeneration of the water
softener for a predetermined time period after the change to the
15. The apparatus of claim 10 wherein the removal means includes
a membrane across the flow path of the sample of water exhibiting
Water softener description
BACKGROUND OF THE INVENTION
In water softening, utilizing the zeolite or ion exchange process,
divalent or hardness, calcium and magnesium ions are replaced by
monovalent ions. In the case of a sodium form water softener the
hardness ions are replaced by sodium ions. This leaves a product
water or outflow from the water softener that has a very slight
conductivity difference from the hard water feed. The problem is
compounded if the feed has a high sodium ion background, as the
conductivity differences between product and feed will be minute.
The renders difficult the detection of water softener exhaustion
by merely measuring the conductivity of the effluent.
It is accordingly an object of the invention to provide a system
for detecting exhaustion of a water softener and controlling the
regeneration thereof which does not depend upon high degree of sensitivity
in the measurement of product conductivity or continuous recalibration
under various conditions of operation which would be necessary in
the utilization of highly sensitive conductivity measurement instruments.
Other and further objects, features and advantages will become
apparent as the description proceeds.
SUMMARY OF THE INVENTION
In carrying out the invention in accordance with a preferred form
thereof the softened water product or outflow from a water softener
is subjected to means for discriminating between monovalent and
divalent ions. This is done by differentially rejecting monovalent
and divalent ions from the product. Differential rejection is preferably
done by means of a reverse osmosis unit.
Then conductivity is measured both before and after the product
has flowed through the reverse osmosis unit, and the two conductivities
are compared. When the water softener has become exhausted the difference
between the two conductivities becomes much greater and an indication
of water softener exhaustion is provided. The conductivities are
in the ratio 10:1 when the softener is functional, and increase
to higher value, e.g. 100:1 when the softener has become exhausted.
A better understanding of the invention will be afforded by the
following detailed description considered in conjunction with the
accompanying drawing in which:
FIG. 1 is a schematic diagram of an embodiment of the invention
for indicating exhaustion of a sodium type water softener column;
FIG. 2 is a schematic diagram of a modification in the apparatus
of FIG. 1 illustrating the manner in which the detection system
is employed for automatically effecting regeneration of a water
Like reference characters are utilized throughout the drawing to
designate like parts.
As represented in the drawing there is a tank 11 containing a column
of ion exchange material such as zeolite resin 12 with an inlet
pipe 13 for the feed of hard water to be treated. There is an outlet
pipe 10 for delivering the softened water or product and a sample
pipe 14 for supplying a sample to be tested.
In accordance with the invention a unit 15 is connected to the
sample pipe 14 for discriminating between monovalent and divalent
ions in the product by differentially rejecting such ions. A suitable
ion discriminator takes the form of a reverse osmosis unit such
as described in U.S. Pat. No. 3133137 of Loeb, Sourirajan and
Weaver issued May 12 1964. However, the reverse osmosis unit may
be of any desired type such as a spiral wrap type cartridge. The
tubular, hollow fiber, or flat plate and frame configuration may
also be used. A standard cellulose acetate reverse osmosis membrane
or other suitable membrane having different rejections for mono-
and di-valent ions may be utilized.
The reverse osmosis unit 15 has an outlet pipe 16 for the product
of the reverse osmosis unit and a discharge pipe 17 for the rejected
brine stream with any suitable type of back pressure device 18 on
the brine stream. A first through-flow conductivity cell 19 is connected
in the sample line 14 in advance of the reverse osmosis unit 15
and a second through-flow conductivity cell 21 is connected in the
product line 16 for the outflow from the reverse osmosis unit 15.
Suitable means are employed for comparing the conductivities measured
in the two conductivity cells 19 and 21. For example, as illustrated
schematically, there may be a source of electrical current 22 connected
in series with the conductivity cell 19 through one coil 23 of a
conventional ratio meter and connected in series with the conductivity
cell 21 through a second coil 24 of the ratio meter 25 having a
pointer 26 cooperating with a scale 27 calibrated in some convenient
Alternatively, the instrument 25 may be provided with contacts
28 and biasing means (not shown) for causing the contacts 28 to
close only when the relationship between the currents flowing in
the conductivity cells 19 and 21 reaches the value corresponding
to water softener column exhaustion.
Although the conductivity detection elements 19 and 21 have been
shown as flow type conductivity cells, the invention is not limited
thereto and does not exclude the use of other suitable types of
conductivity measuring elements such as screw-in or other type conductivity
measurement devices. They may be composed of glass, epoxy or other
materials or construction, whether or not temperature compensated.
The instrument 25 may be employed for actuating an alarm, recorders
or various output devices (not shown).
The apparatus will operate efficiently at any pressure above the
osmotic pressure of the feed solution. Typically this will be approximately
60 pounds per square inch. As shown, the ion discrimination apparatus
15 is installed so that its feed through the line 14 will be from
a point slightly above the bottom of the softener column 12 so that
total exhaustion of the zeolite softening resin can be anticipated.
This feed will contain sodium ions as the primary cation, since
the softener column acts to replace other cations with sodium. The
rejection of a standard cellulose acetate reverse osmosis membrane
toward sodium is normally 90%, and therefore the product water from
outlet pipe 29 will have a conductivity approximately one tenth
that of the water in the line 14 from the softener column 12. By
suitable selection of cell constants the signals from the two cells
19 and 21 can be balanced in the instrument 25. Alternatively, the
balance or zero point may be adjusted by suitable biasing means
such as biasing springs or by selection of a suitable point on the
scale 27 as the zero value.
It will be understood that in case the current source 22 is a direct
current source and the magnetic field in which the coils 23 and
24 rotate is supplied by a permanent magnet 31 the coils 23 and
24 shown as crossed coils mounted upon a pivoted rotatable unit
(not shown) will take up a position in which the tendency for each
coil 23 and 24 to become aligned with the magnetic field will be
When the column 12 breaks through or becomes exhausted and calcium
and magnesium ions are no longer replaced with sodium ions, the
sodium content in the supply through sample line 14 to the reverse
osmosis unit 15 decreases and the divalent ion content increases.
The cellulose acetate membrane in the unit 15 has a rejection toward
divalent ions of close to 99%, and therefore the amount of divalent
ions in the product line 29 will be 1% or less of the feed. The
amount of sodium in the product will also decrease, since the membrane
rejects 90% of the feed concentration of sodium and the sodium content
in the feed will decrease in proportion to the divalent increase.
This will cause the conductivity meter to become unbalanced from
its normal position, giving an indication of column breakthrough.
As an example, if water containing 500 ppm NaCl with 500 ppm CaCl.sub.2
were softened, the product water would contain 1026 ppm NaCl. Assuming
the conductivities to be additive, the feed conductivity would be
1000 .mu.mhos/cm (NaCl) plus 1100 .mu.mhos/cm CaCl.sub.2) = 2100
.mu.mhos/cm. The product conductivity would be 2050 .mu.mhos/cm.
The feed water to the reverse osmosis unit 15 before the column
is exhausted will contain 1026 ppm NaCl (2050 .mu.mhos/cm). The
reverse osmosis product water will contain 103 ppm NaCl (220 .mu.mhos/cm),
assuming a 90% rejection. When the column breaks through or is exhausted,
the feed to the reverse osmosis unit will contain 500 ppm NaCl (1000
.mu.mhos/cm) and 500 ppm CaCl.sub.2 (1100 .mu.mhos/cm). The sodium
rejection will be 90%, but the calcium rejection will be 99%. Therefore,
the reverse osmosis product water will contain 50 ppm NaCl (106
.mu.mhos/cm) and 5 ppm CaCl.sub.2 (15 .mu.mhos/cm). The conductivity
of this water will be 121 .mu.mhos/cm, or an approximate 50% decrease,
readily observable on standard conductivity equipment.
The novel use of a reverse osmosis membrane unit to separate hardness
or divalent cations from sodium or monovalent cations, and measuring
the difference in conductivity change as an indication of the presence
of hardness, enables the hardness in water and softener exhaustion
to be measured relatively inexpensively with rugged and reliable,
Thus, it becomes unnecessary to rely upon the use of ion selective
electrodes, which are sensitive to fouling, breakage, etc. and require
expensive monitoring equipment or to rely upon the use of a colorimetric
analysis. Moreover, the arrangement of the invention is useful over
the entire concentration range and is unaffected by a high background
of sodium ion in the unsoftened water.
Although the conductivity cells 19 and 21 have been illustrated
and described as mounted in lines 14 and 16 before and after the
reverse osmosis unit 15 the invention is not limited thereto. The
invention does not exclude mounting the conductivity cells 19 and
21 in lines 14 and 17 or in lines 16 and 17 for example. Thus,
the conductivity cells may be used to monitor sample feed and brine,
sample feed and water product of the reverse osmosis unit or product
Apparatus of the foregoing type is useful whenever it is necessary
to discriminate between any ion concentrations, as long as the two
different ions are rejected to different extents by the reverse
osmosis membrane. This differing rejection may be achieved by using
a different membrane or by using some chemical additive to the feed
which will alter the rejections of the ions.
Moreover, the arrangement is useful for high conductivity waters
as well as those of low conductivity.
Although a ratio-type instrument 25 has been illustrated in FIG.
1 and described in connection with the operation of that apparatus,
it will be understood that the invention is not limited thereto
and does not exclude the use of a differential type of device such
as the differential relay 41 illustrated in FIG. 2 having opposing
coils 42 and 43 in series with conductivity cells 19 and 21 respectively
and acting differentially upon an armature carrying a movable contact
44 adapted to close a circuit to a stationary contact 45 to close
an actuating circuit in a time switch 46 when the softener column
As shown in FIG. 2 the time switch 46 may be connected to actuate
a torque motor 40 serving to reverse the positions of various valves
in the water lines. During normal operation of the water softening
system, the following valves are open: valve 47 in sample line 14
valve 48 in line 13 and valve 55 in the soft water output line 10;
and the following valves are closed: valve 49 in waste discharge
or purging line 51 from the tank 11 valves 52 and 53 bypassing
the valve 48 and connecting the input line 13 and the tank 11 to
a regenerator salt supply 54. When the time switch 46 is actuated
by closure of the contacts 45 and 44 the torque motor 40 is energized
to rotate each of the valves to its opposite condition so that water
flows through the input line 13 through valve 53 regenerator 54
valve 52 tank 11 waste discharge pipe 51 and discharge valve 49
while valves 55 and 47 are closed to prevent delivery of salt water
through the output line 10 and the sample line 14 and the valve
48 is closed to cause all of the feed water to flow through the
regenerator 54. Then after the lapse of the time set by the time
switch 46 determined by the characteristics of the system, regeneration
ceases and the original valve connections are restored. If desired,
the arrangement may be such as to delay the reopening of the valves
47 and 55 so as to flush the column 12 with clean water before restoring
flow through the valve 55 and the product line 10.
While certain embodiments of the invention have been fully illustrated
and described, it will be obvious to those skilled in the art that
various modifications and alterations may be made therein and it
is intended to cover all such modifications and alterations as may
fall within the spirit and scope of the invention.