Note: Descriptions are shown in the official language in which they were submitted.
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WATER SOFTENER SYSTEM USING NANOFILTRATION TO RECLAIM
A PORTION OF THE REGENERATING SOLUTION
CROSS-REFERENCE TO RELATED APPLICATIONS
This is a continuation-in-part application filed under 37 CFR 53(b) claiming
priority
under 35 U.S.C. 120 of co-pending U.S. patent application Ser. No. 12/842,644
filed July
23, 2010, which claims priority from U.S. patent application Ser. No.
10/587,955 having a
371(c) filing date of July 31, 2006 which is a U.S. national election
consistent with 35 U.S.C.
363 of international patent application Ser. No. PCT/US05/02537 filed January
28, 2005
claiming priority under 35 U.S.C. 119(e) (1), of provisional application Ser.
No. 60/540,396,
having a filing date of January 30, 2004, each of which is incorporated herein
by reference in
their entireties.
FIELD OF THE INVENTION
The present invention relates to water softening systems. In particular, the
present
invention relates to a water softening system having a filtration system that
separates hardness
ions from a softening solution so that the softening solution can be reused
instead of being
discharged with the hardness ions into a drain.
BACKGROUND OF THE INVENTION
Among industrialized nations of the world, there is a growing concern for, and
emphasis on, environmentally responsible practices. For example, more and more
governments and communities are interested in minimizing the kinds and
quantities of
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chemicals that are deposited into water systems, including wastewater systems.
A common
form of wastewater pollution is the alkali metals such as sodium and potassium
discharged
into sewers or septic systems during typical regeneration processes of water
softeners.
For the last fifty years or so, water softening has become widely used in
those regions
where water supplies contain high concentrations of calcium and magnesium, and
are
therefore considered "hard". Utilizing a sodium or potassium ion exchange
process,
resin-based water softeners are installed on water lines, particularly those
leading into
residences, to soften most if not all of the water used inside such homes. As
a water supply
passes through ion exchange resins inside a water softener, the calcium and
magnesium ions
bond to the resins and are removed from the water flow.
Periodically, these ion exchange resins must be regenerated by removing the
hardness
ions on the resins. Typically this regeneration is accomplished utilizing by
washing the resins
with an aqueous solution of alkali metal salts such as sodium or potassium
chloride. The
term "regenerant" in this application means "a liquid suitable for causing
sodium or
potassium to replace hardness ions on the surface of the softening resin."
In a typical regeneration process, the regenerant is slowly pumped through the
resin
bed. Through a chemical exchange process, the calcium and magnesium ions which
were
adsorbed onto the resin during the softening process are stripped off the
resins and replaced
with sodium or potassium ions. At the conclusion of this process, the "spent"
solution
containing both the hardness ions and the regenerant is discharged into the
sewer or septic
system. It is this discharge that has serious long-term effects on the
environment, as the
regenerant salinity, total dissolved solids, and/or chloride cause corrosion
in the sewage
system, and contaminate the planet's fresh water supplies.
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Presently, because this pollution problem has defied resolution by
economically
acceptable means, some communities are resorting to banning or limiting water
softening in
homes. For example, on October 12, 2009, California governor Arnold
Schwarzenegger
signed into law, a bill giving local California water agencies the authority
to restrict or even
to ban the use of water softeners using on-site salt-based regeneration.
Scientific studies such as one conducted by Santa Clarita, California are
finding that
regenerant discharged from water softeners is a significant source of water
pollution. This
finding supports prohibitions of, or restrictions on, current commercially
available water
softening systems. Consequently, removing the alkali salts from the spent
regenerant before
the solution is discharged has become an immediate and real concern both for
communities
that want soft water and for water softener manufacturers.
SUMMARY OF THE INVENTION
The present invention relates to an improved water softener system comprising
apparatus by which the apparatus operates to separate hardness ions from
regenerant in a way
to allow most of the regenerant to be reclaimed, thereby reducing the
discharge of regenerant
into the environment.
Nanofiltration (NF) is a pressure driven, membrane separation technology that
separates ionic solute from water supplies based on the ionic charge of the
solute. Preferred
embodiments of the present invention include a pump that supplies the force
required to
effect the separation and the feeding of a regenerant or feed stream into a
housing containing
a nanofilter membrane element.
In the NF process, multivalent salts are rejected to a higher degree than
monovalent
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salts. Thus, NF used as part of a water softener system can be used to
selectively remove the
multivalent hardness ions from a regenerant and direct them to a drain while
monovalent salts
that make up the regenerant are recycled to a water softener brine tank. With
the present
invention, approximately 90% or more of the regenerant that typically is
discharged into a
drain can be recovered and recycled, thereby minimizing water pollution as
well as the cost of
water softener salt from which regenerant is prepared.
The softener system of the invention has normal and regeneration modes. During
normal mode, hardness ions exchange positions with salts ions held onto the
resin particles.
When most of the salts on the resin particles has been replaced with hardness
ions, the
softener system goes into regeneration mode.
The invention's regeneration mode has two phases of operation that are
modifications
of the current industry standard. These modifications substantially reduce the
amount of salt
discharged into the drain during regeneration.
The apparatus regenerates a water softening system that removes multivalent
ions
from water provided by a hard water source, and recovers at least a portion of
the
regenerating salt used for the regeneration. Such a water softening system
conventionally
includes a softener tank through which the water from the source passes from
an upstream
end thereof to a downstream end thereof, and a brine tank for holding a
regenerant comprising
monovalent ions.
A first diverter valve supplies liquid selectively from either the water
source or the
brine tank to the upstream end of the softener tank depending on the system's
current mode.
For improved regeneration, the system includes a nanofilter having upstream
and downstream
sides. The upstream side of the nanofilter has an inlet and an outlet, and the
downstream
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25 side has an outlet. The nanofilter passes monovalent ions to the
downstream side and retains
multivalent ions on the upstream side;
A second diverter valve is connected to receive liquid from the downstream end
of the
softener tank and to selectively supply liquid at a first outlet to a water
distribution system
and to a second outlet. There is a connection between the downstream side
outlet of the
30 nanofilter and the brine tank. A first throttling valve is connected
between the upstream side
outlet of the nanofilter.
A pump receives liquid from the second outlet of the second diverter valve and
supplies pressurized liquid to the upstream side inlet of the nanofilter. A
third diverter valve
has an inlet and first and second selectable outlets. The third diverter valve
inlet is connected
35 to receive liquid from the second outlet of the second diverter valve.
The first outlet of the
third diverter valve is connected to the pump, and the second outlet of the
third diverter valve
connected to another destination.
A controller in response to a regeneration signal enters the system into a
regeneration
mode. During a first phase of the regeneration mode the controller:
40 a) operates the first diverter valve to pass regenerant from the brine
tank through the softener
tank of the water softening system;
b) operates the second diverter valve to direct liquid from the downstream end
of the softener
tank to the second outlet of the second diverter valve; and
c) operates the third diverter valve to supply liquid from the second outlet
of the second
45 diverter valve to the first outlet of the third diverter valve.
During a second phase of the regeneration cycle which follows the first phase
of the
regeneration cycle, the controller operates the third diverter valve to direct
liquid from the
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second diverter valve to the second outlet of the third diverter valve.
The apparatus further includes a buffer tank interposed between the third
diverter
50 valve's first outlet and the pump, and the controller operates the
second and third diverter
valves to direct liquid from the downstream end of the softener tank to the
buffer tank during
the regeneration cycle.
The first throttling valve in one preferred embodiment of the apparatus has a
pressure
drop that causes from 5 ¨ 25% of the flow to the nanofilter's upstream side
inlet to divert
55 through the upstream outlet to the drain.
Another version of the softening system also comprises a pipe between the
third
diverter valve's second output and the drain. During the second, fast rinse
phase of the
regeneration mode, liquid having almost no hardness ions and little alkali
metal ion
concentration may be directed to the drain with little harm. The controller
accomplishes this
6 0 by causing the third diverter valve to connect the inlet thereof to the
second outlet during the
second phase of the regeneration mode.
The apparatus may further include an alkali metal ion concentration (salinity)
detector
receiving liquid from the second diverter valve's second outlet. The alkali
metal ion
concentration (salinity) detector provides a signal indicating the salinity of
the received
6 5 liquid. Upon detecting the salinity of said liquid to be below a
preselected concentration, the
alkali metal ion concentration detector sets the third diverter valve to
connect the inlet thereof
to the second outlet thereof. In one embodiment, this detector measures the
conductivity of
the liquid that the second diverter valve's second outlet provides.
In regeneration mode, during a first slow rinse phase, the system uses
modified
70 diverter valves to direct the effluent during this phase through a
nanofilter to the brine tank.
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During a later fast rinse phase, at least a portion of the water in the
softener tank that has
dissolved salt may also be directed to the brine tank.
The system is also compatible with a further improvement that, while the
softener is
in normal mode, allows the nanofilter to process the contents of the brine
tank, removing and
discharging any remaining hardness ions in the brine tank.
BRIEF DESCRIPTION OF THE DRAWING
The FIG. is a diagram of a water softener system including water treatment by
a
nanofilter allowing reuse of the softener salt.
DETAILED DESCRIPTION OF THE INVENTION
Referring to the FIG., a water softening system 10 according to the invention
conventionally includes a connection to a source 20 of hard water to be
softened such as a
municipal water main or a well. During a normal operating mode or cycle, water
from source
20 is directed to an input connection of a softener tank 19. Tank 19 contains
resin particles
on which hardness ions in the water adsorb to soften the water as it flows
through tank 19.
The softened water from tank 19 is then supplied to a user such as a building
through a
plumbing connector 40.
Also conventionally, system 10 operates in addition to the normal mode, in a
regeneration mode. The regeneration mode has a first slow rinse phase during
which bivalent
hardness ions adsorbed onto the resin particles are replaced by monovalent
salt ions by flow
of regenerant from a brine tank 43. A fast rinse phase follows the slow rinse
phase, during
which salt remaining in the liquid within softening tank 19 is flushed from
tank 19.
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Operation of system 10 is controlled in part by a controller 14 which selects
the
settings of first through third diverter valves 17, 35, and 45. Controller 14
receives a
regeneration signal on a path 15. The signal may be generated by nothing more
than a clock
sequencer or may comprise internal signals of a microprocessor that serves as
controller 14.
Each of these diverter valves 17, 35, and 45 operates in a similar way. A
control
signal supplied by controller 14 on a group of paths 16 sets the operating
state for each of the
diverter valves 17, 35, and 45 dependent on the desired operating mode of
system 10. These
operating modes of system 10 are normal, slow rinse regeneration, and fast
rinse regeneration.
In a first diverter valve state, an "a" or first internal path of the diverter
valve is open
and a "b" or second internal path is closed. In the first state, liquid flows
through the "a' path
only. In a second diverter valve state, liquid flows through the "b" path and
the "a" path is
closed.
Controller 14 also manages the operation of a pump 51. A control signal on a
path 22
causes pump 51 to operate as controller 14 specifies during the regeneration.
Diverter valve 45 may also be controlled by an optional conductivity test
element 78
receiving a conductivity signal from a conductivity sensor 70, also optional.
In all other
respects, operation of diverter valve 45 is identical to that of diverter
valves 17 and 35.
First and second diverter valves 17 and 35 control the operating mode in a
conventional softening system. First diverter valve 17 has first and second
inputs to "a" and
"b" paths, from source 20 and brine tank 43 respectively. Valve 17 selectively
directs the
liquid from the selected input to an output 21 as specified by controller 14.
Second diverter valve 35 receives liquid from softener tank 19 in pipe 27 at
the input,
and selectively directs this liquid along "a" and "b" paths to first and
second outputs
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respectively as specified by a schematically shown controller 14. In a
conventional system,
the "b" or second output of valve 35 flows to a drain. In both a conventional
system and in
system 10, water flows from the "a" or first output of valve 35 to users
through connection
40. In conventional systems, valves 17 and 35 are typically combined in a
single physical
unit with functionality as shown.
During normal mode, diverter valve 17 causes liquid to flow only from source
20 to
softener tank 19 and diverter valve 35 allows water to flow only from softener
tank 19 to
connection 40. Thus, in normal operating mode, water flows from source 20 to
softener tank
19 and from there to connection 40 for distribution to the building.
In response to a regeneration signal on path 15, controller 14 starts the
regeneration
mode by closing the "a" paths and opening the "b" paths of valves 17 and 35,
thereby shutting
off water flow from source 20 to softener tank 19 and to plumbing connection
40. For this
reason, regeneration is preferably done when little or no water usage occurs
such as during
nighttime. The design of diverter valve 17 may also directly connect source 20
to connection
40 during regeneration, to provide unsoftened water to users during that time.
The improved softening system 10 shown in the FIG. has modifications compared
to
current systems during the handling of liquid from softening tank 19 in
regeneration mode.
As mentioned, the regeneration mode has a slow rinse phase, followed by a fast
rinse phase
that clears residual salt from the softener tank 19. Controller 14 selects the
normal and
regeneration modes responsive to the regeneration signal on path 15 and during
the
regeneration mode, the two phases of the regeneration mode.
The description hereafter explains the improvements found in the regeneration
mode
of system 10. In system 10, diverter valve 35 directs the effluent from the
regeneration cycle
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back to brine tank 43 through a buffer tank 53, a pump 51, and a nanofilter
(NF) 25 rather
than directly to a drain. Nanofilter 25 has a high pressure inlet to which
pipe 23 from pump
51 attaches, a high pressure outlet to which pipe 32 attaches, and a low
pressure outlet to
which pipe 28 attaches.
The system 10 includes additional elements to efficiently reuse or reclaim a
substantial percentage of the regeneration salts. Thus, system 10 provides for
directing much
of the liquid bearing salt ions flowing from the softening tank 19 during both
the slow and
fast rinse phases back to brine tank 43. The flow of liquid to brine tank 43
during the fast
rinse phase may stop when of salinity of this liquid falls below a
predetermined level or when
tank 43 is full.
The structure of third diverter valve 45 is functionally very similar to that
of second
diverter valve 35. The second, "b" path of second diverter valve 35 connects
to the inlet of
third diverter valve 45. The first or "a" path in third diverter valve 45
connects to buffer tank
53. The second, "b" path of third diverter valve 45 connects directly to the
drain.
During the slow rinse phase, the "b" path of both first and second diverter
valves 17
and 35 is open and the "a" path of valve 45 is open. Regenerant from tank 43
flows through
softener tank 19 picking up divalent hardness ions such as calcium adsorbed on
the resin
particles. Liquid comprising this regenerant/hardness ions solution then flows
from the
softener tank 19 through the "b" path of valve 35 to the inlet of valve 45.
During the slow rinse phase, controller 14 holds the "a" path of diverter
valve 45 open
allowing liquid carrying the hardness ions and regenerating salt to flow from
valve 35 through
pipe 48 to buffer tank 53. The liquid then flows to pump 51 and the inlet of
nanofilter 25.
During the slow rinse phase, controller 14 activates pump 51, which supplies
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pressurized liquid from buffer tank 53 through pipe 23 to nanofilter 25 having
an element
25a. Pump 51 increases the pressure of the regenerant with the dissolved
hardness ions to
perhaps 100 ¨ 150 psig. A throttling valve 31 connects the upstream side of
nanofilter 25 to a
drain.
Element 25a typically comprises a spirally wound membrane that blocks a
substantial
percentage of the hardness ions and allows a high percentage of the salt ions
to pass through
the membrane. The NF membrane element 25a has an upstream or high pressure
side
(indicated as NFH) and a downstream, low pressure side (indicated as NFL) that
is at
essentially atmospheric pressure. The NFH side has an inlet to which pipe 25
connects and
an outlet connecting to pipe 32 carrying a liquid with a high concentration of
hardness ions.
The liquid on the downstream side of nanofilter 25 comprises a liquid permeate
stream provided to a pipe 28. The liquid permeate stream has a reduced
concentration of the
hardness ions, and a relatively high concentration of sodium or potassium
ions.
The permeate stream returns to brine tank 43 through pipe 28, a check valve
56, and a
pipe 29. The absence of the hardness ions in the permeate stream in pipe 28
results from the
flow of the regenerant through the NF membrane element 25a. Check valve 56 may
be
integral with nanofilter 25.
Buffer tank 53 may be unnecessary in some systems. In some types of softener
systems whose flow of regenerant through softener tank 19 during slow rinse is
greater than
the capacity of nanofilter 25, buffer tank 53 may be interposed between valve
45 and pump
51 to allow a suitable flow rate of regenerant through softening tank 19. Over
a period of
time, pump 51 then draws down any excess liquid in tank 53.
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The liquid that does not pass through the NF membrane element 25a has a high
concentration of hardness ions (relative to the NFL side of element 25a). This
concentrate
stream thus contains most of the hardness ions in the liquid flowing in pipe
23 and possibly a
small amount of regenerant. Liquid not passing through nanofilter 25 flows
through a pipe 32
to throttling valve 31 and from valve 31, to the drain. Throttling valve 31
and membrane 25a
cooperate to divide flow between membrane element 25a and throttling valve 31.
Valve 31
may comprise an orifice or other pressure-dropping device.
The high pressure at the NFH side of membrane 25a forces a major portion of
the
pumped liquid through membrane element 25a. The pressure drop across both
membrane
element 25a and throttling valve 31 are each approximately equal to each other
and to the
pump 51 pressure, assuming the brine tank 43 is maintained at approximately
atmospheric
pressure.
In one preferred embodiment, throttling valve 31 comprises a flow restrictor
such as
an orifice whose pressure drop relative to element 25a divides the liquid flow
from pipe 23 so
that approximately 75 ¨ 95% of this liquid flows through element 25a to brine
tank 43 and
approximately 5 ¨ 25% flows through throttling valve 31 to the drain. 90% of
the flow in
pipe 23 reaching pipe 28 is one current preferred value.
Almost all of the bivalent hardness ions in the liquid supplied by pipe 23 are
contained in the liquid flowing through the high pressure outlet of nanofilter
25 to pipe 32.
The salt concentration in the liquid carried by both pipes 28 and 32 is nearly
equal. However,
most of the liquid flowing in pipe 23 passes through membrane 25a and returns
to brine tank
43, thereby substantially reducing both the volume of drain water and the
total mass of salt
entering the drain. Since the flow of liquid through throttling valve 31 is
substantially less
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than that through nanofilter 25, most of the salt ions in the flow through
pipe 23 thus return to
brine tank 43. Directing most of the flow through pipe 23 to flow through
nanofilter 25 to
brine tank 43 dramatically reduces the total amount of salt flowing to the
drain.
Preferably, the membrane element 25a has a spiral-wound configuration,
although
other configurations are possible, such as capillary fiber, tubular, or plate
and frame. A
common configuration for such a membrane 25a comprises many turns of a strip
of
membrane material with the edges sealed in some manner to cause a great
majority of the
liquid entering the NFH side to either pass through the membrane 25a pores or
flow to valve
31.
The following examples, without limitation, are types of NF membrane elements
25a
that are acceptable for use in the present invention, although their
manufacturers may or may
not have their products evaluated for this application: a spiral wound NF-270
membrane
made by Dow Filmtec; a spiral-wound XN45 membrane made by TriSep Corp.; a
spiral-wound SR2 membrane, by Koch Membrane Systems; a spiral-wound NF
membrane
using a special polymer, by Hydranautics; and a spiral-wound NF membrane using
a special
polymer, by GE Osmonics.
Generally, a suitable NF membrane element 25 has a minimum of approximately
90%
multivalent salts rejection and a maximum of approximately 20% monovalent
salts rejection.
If the concentration of the regenerant in tank 43 is maintained above
approximately 10%
alkali salts, pH adjustment is usually unnecessary. NF membrane element 25 can
remove
hardness ions from unmodified regenerant in buffer tank 53. The term
"unmodified" in this
context refers to regenerant that has not been subjected to pH adjustment or
other chemical
treatment before passing to NF membrane element 25.
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In conventional systems during the fast rinse phase, controller 14 closes the
"b" path
of valve 17 and opens the "a" path for a period of time. Valve 35 remains with
the "a" path
closed and the "b" path open. This allows water from source 20 to flush salts-
containing
liquid from softener tank 19. In a conventional system, this salt-containing
liquid flows
directly to the drain. Eventually controller 14 sets both valves 17 and 35 to
activate their "a"
paths, ending the regeneration mode.
Pipe 32 also connects to a throttling valve 61 which then connects to an input
of
buffer tank 53. The flow rate along the high-pressure side of NF membrane
element 25a
from the inlet to the high pressure outlet at pipe 32 should be high enough to
maintain
1 0 sufficient turbulence adjacent the membrane 25a surface to limit
fouling. This may be
accomplished by directing a portion of the liquid leaving the high pressure
outlet of
nanofilter 25 through line 32 to throttling valve 61 and back into tank 53.
The system 10 may also include a further improvement relating to the fast
rinse
phase. Liquid flowing through path "a" of diverter valve 45 during the fast
rinse phase first
flows through a conductivity sensor 70. Sensor 70 provides a conductivity
signal to a
conductivity tester 78. The conductivity signal indicates the conductance of
the liquid
flowing through sensor 70, which indicates the concentration of salts or
alkali metal ion
concentration (salinity) in this liquid. When the conductivity signal
indicates a salts
concentration below a preselected level, tester 78 supplies a signal on path
81 to diverter
valve 45 overriding the signal on path 16 to close path "a" and open path "b".
The fast rinse
liquid carried by pipe 41 at this point in the fast rinse cycle contains a
sufficiently low salts
concentration that directing fast rinse liquid to the drain is harmless.
During at least the first part of the fast rinse phase of regeneration
however, tester 78
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may detect salts concentration in the flow through sensor 70 to be above the
preselected
The open "a" path of valve 45 directs this relatively concentrated regenerant
back to the
tank 43 through pump 51 and nanofilter 25. Of course, the amount of liquid
flowing to
tank 53 must not cause either buffer tank 53 or brine tank 43 to overflow, so
the level at
which tester 78 changes the setting of diverter valve 45 must be properly
selected.
To summarize, this improvement serves two purposes. First of all, some salts
rinsed
from softener tank 19 during the fast rinse cycle return to brine tank 43,
further reducing the
amount of salt sent to the drain. Secondly, the water lost to the drain during
regeneration is
replaced by previously used water, so the overall regeneration process uses
less water.
The FIG. shows further improvements related to monitoring the functionality of
nanofilter 25. A pressure sensor 64 is connected between the nanofilter inlet
23 and
nanofilter low pressure outlet 28 and provides a pressure difference signal to
a pressure test
element 67 encoding the pressure difference sensed by sensor 64.
If the sensed pressure difference is outside of a preselected range the test
element 67
provides a fault signal of some kind, such as an appropriate indicator light.
In this way both
clogging and perforation of nanofilter 25 will be detected. The range will be
determined by
pump and nanofilter 25 characteristics.
The FIG. shows another pressure sensor 84 monitoring the functionality of
nanofilter
25. Pressure sensor 84 is connected between the nanofilter inlet 23 and the
nanofilter high
pressure outlet 32 and provides a pressure difference signal to a pressure
test element 87
encoding the pressure difference sensed by sensor 84. Sensor 70 and tester 78
together
comprise a salinity detector.
If the sensed pressure difference is outside of a preselected range the test
element 87
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provides a fault signal of some kind, such as an appropriate indicator light.
Recall that
nanofilter 25 is configured as a spirally wound filter element. It is possible
that after
extended usage, the passage within filter element 25a from pipe 23 to pipe 32
will partially
clog. The pressure drop between pipes 23 and 32 will increase due to this
clogging. By
detecting this increased pressure drop, the clogging of nanofilter 25 will be
detected. The
appropriate pressure drop to indicate clogging will be determined by pump and
nanofilter 25
characteristics.
Although the preferred embodiments of the NF water treatment system for water
softeners have been described herein, it should be recognized that numerous
changes and
variations can be made to these embodiments, which changes and variations are
still within
the scope and spirit of the present invention. The present invention should
not be unduly
limited by the illustrative embodiments and examples set forth herein for
exemplary
purposes. Rather, the scope of the present invention is to be defined by the
claims.
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