Abstract:
An apparatus, for use with a reverse osmosis system comprising a feed input, a concentrate output, and a permeate output, includes (i) at least one pressure sensor operative to measure a pressure of at least the permeate output of the reverse osmosis system and to generate a signal indicative of the pressure of at least the permeate output of the reverse osmosis system and (ii) at least one controller operative to adjust a speed of at least a first pumping mechanism based at least in part on the signal indicative of the pressure of at least the permeate output of the reverse osmosis system. The first pumping mechanism comprises at least one of: (i) a fluid input coupled to at least the permeate output of the reverse osmosis system; and (ii) a fluid output coupled to at least the feed input of the reverse osmosis system.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Technical Field 
         [0002]    This invention relates generally to techniques and devices for providing more effective monitoring and adjustment of operational conditions within a reverse osmosis system or other filtration system, and more particularly to techniques and devices that provide improved pressure monitoring and/or pump speed control in such a system. 
         [0003]    2. Background Art 
         [0004]    The present invention is useful for enhancing the performance of a reverse osmosis system. Although reverse osmosis is perhaps best known for its use in connection with desalinization, it is also widely used to purify fresh water for medical, industrial, and domestic applications. In addition to water, reverse osmosis is also used in connection with other fluids. such as milk and wine, for example, in agricultural applications. 
         [0005]      FIG. 1  is a block diagram which depicts a reverse osmosis system according to the prior art. Input  101  permits a solvent to enter. This solvent may be water, such as sea water, brackish water, tap water or wastewater, and typically has various solutes (including, but not limited to, sea salt) dissolved therein. 
         [0006]    Pretreatment assembly  110  may be included in order to prepare the input  101  for processing by the reverse osmosis (RO) filter  130  by, for example, removing particulates and/or chemicals which can damage the membrane  133  within RO filter  130 . Certain embodiments may omit pretreatment assembly  110 . 
         [0007]    The output  121  from pretreatment assembly  110  is coupled to a valve  122  which serves to modulate the pressure and flow rate of the input  123  to feed pump  124 . For example, valve  122  may be configured to shut off input  123  to feed pump  124  (and hence input  131  to RO filter  130 ) under certain conditions. Valve  122  is preferably electronically actuated, and may be of any suitable type, including but not limited to solenoid valves and/or ball valves. 
         [0008]    A solvent having solutes dissolved therein (often called “feed”) enters the RO filter  130  through input  131 . In order to force solvent through membrane  133  within RO filter  130 , it is necessary to apply a pressure in excess of the osmotic pressure to the input  131  of the RO filter  130 . Feed pump  124  (sometimes referred to as a “booster pump”) may be used to apply this pressure to the input  131  of the RO filter  130 . Feed pump  124  may have a motor coupled thereto and/or incorporated therein. Feed pump  124  may be of any suitable type, including but not limited to displacement pumps (e.g., gear, screw, vane, piston, or diaphragm pumps) and rotodynamic pumps (e.g., centrifugal pumps). 
         [0009]    RO filter  130  consists of a region of high solute concentration  132  and a region of low solute concentration  134  separated by a semipermeable membrane  133 , which has pores of a size (often as small as 0.1 nm) which allows the solvent but not the solute to pass therethrough. Membrane  133  may be made from a variety of materials, including but not limited to, cellulose acetate (e.g., cellulose triacetate (CTA) or cellulose acetate blend (CAB)) or a thin film composite (TFC) which may include, for example, composite polyamide (CPA). Other suitable TFC membranes may comprise one or more of polyamide, polymide, polysulfone, polyethersulfone, polyurea, and polyetherurea. Membrane  133  may be formed in a variety of configurations, including but not limited to spiral-wound, hollow-fiber, tubular and/or plate and frame. Examples of suitable materials and configurations for membrane  133  include those described in a paper entitled “Commercial RO Technology,” published by Hydranautics and dated Jan. 23, 2001, which is submitted herewith and incorporated by reference herein. 
         [0010]    A solvent having solutes dissolved therein (often called “feed”) enters the region of high solute concentration  132  at high pressure through input  131 . This pressure forces the solvent through the semipermeable membrane  133  from the region of high solute concentration  132  to the region of low solute concentration  134 , while the solutes remain within the region of high solute concentration  132 . This movement of the solvent (but not the solutes) into the region of the low solute concentration  134  results in a further decrease in the solute concentration within the region of low solute concentration  134 , thereby forming a purified solvent referred to as the “permeate,” which exits at low pressure through permeate outlet  151 . By contrast, the movement of the solvent (but not the solutes) from the region of high solute concentration  132  will result in a further increase in the concentration of solute within the solvent which remains within this region, thereby forming a highly concentrated fluid, referred to as a “concentrate” or “retentate,” which exits at high pressure through concentrate outlet  141 . 
         [0011]    In desalinization, the feed may comprise saltwater or brackish water, the permeate may comprise purified fresh water, and the concentrate may comprise concentrated brine. In other forms of water purification, the feed may consist of fresh but impure water (e.g., rain water, tap water or waste water), the permeate may comprise purified and/or deionized fresh water, and the concentrate may comprise highly impure water. Although in the aforementioned applications, the concentrate is typically viewed as an undesirable waste product, in other applications, the concentrate is viewed as desirable, and sometimes is even considered more desirable than the permeate. For example, reverse osmosis is often used within the dairy industry to produce a more concentrated form of milk to reduce shipping costs, or to process whey in order to produce whey powder for use as a nutritional supplement. 
         [0012]    Concentrate outlet  141  is coupled to a restrictor  142 , such an orifice plate, which serves to lower the pressure of the concentrate outlet  141  such that the concentrate may be stored in concentrate storage tank  143 . The concentrate within concentrate storage tank  143  may then be discarded as waste or output as a desirable end-product (e.g., in the aforementioned dairy applications). 
         [0013]    Other arrangements may include additional and/or alternative components for distribution and/or storage of concentrate. For example, concentrate outlet  141  may be coupled to input  131  so that the concentrate is fed back into RO filter  130  in a configuration known as “concentrate recirculation,” or concentrate outlet  141  may be coupled to an input of another RO filter to allow for recovery of additional permeate therefrom in a configuration known as “concentrate staging.” 
         [0014]    Permeate output  151  is coupled to permeate pump  152  (also known as a “permeate pump”), which may be used to provide additional pressure to increase the flow rate of permeate output  151 . As with feed pump  124 , permeate pump  152  may have a motor coupled thereto and/or incorporated therein. Permeate pump  152  may be of any suitable type, including but not limited to displacement pumps (e.g., gear, screw, vane, piston, or diaphragm pumps) and rotodynamic pumps (e.g., centrifugal pumps). 
         [0015]    The output  153  of permeate pump  152  is coupled to check valve  154 , which serves to prevent backflow from downstream components such as storage tank  156 . In the absence of a backflow prevention device such as check valve  154 , backflow entering RO filter  130  through permeate output  151  (e.g., when storage tank  156  is at capacity) could damage membrane  133 , for example, by causing membrane envelopes to expand and/or rupture. Other arrangements may utilize other types of backflow prevention devices, including but not limited to an air gap. a double check (DC) valve and/or a reduced pressure (RP) device. 
         [0016]    The output  155  of check value  154  is coupled to a permeate storage tank  156 . Permeate storage tank  156  (which may be pressurized and/or vented in some embodiments) may be utilized to store at least a portion of the permeate for later use. An output  157  of permeate storage tank  156  may be coupled to a distributor  158 . Distributor  158  may be utilized to output at least a portion of the permeate (e.g., to a faucet). In some embodiments, distributor  158  may include a pump known as a “delivery pump” or “demand pump.” 
         [0017]    Other arrangements may include additional and/or alternative components for distribution and/or storage of permeate. For example, in an arrangement known as permeate staging or two-pass filtering, output  153  and/or  155  could be fed into a second RO filter to further purify the permeate. This may be particularly beneficial in applications where input  101  contains a particularly high concentration of solutes, such as seawater desalinization or wastewater treatment. 
         [0018]    Energy usage is often the single largest factor in the cost of reverse osmosis systems, and can account for 20-30% of the total cost of water. An energy analysis of one reverse osmosis system, as described in FILMTEC Membranes Tech Fact No. 609-00472, submitted herewith and disclosed by reference herein, revealed that almost three-quarters of the energy cost was the result of pressure loss across the membrane, and more particularly within the feed-to-permeate section. The second largest factor in energy cost was inefficiency of the pumps used to apply pressure to the fluid, including the use of throttling valves to control flow from pumps. 
         [0019]    The prior art recognizes these problems and discloses various expedients with a view to solving these problems. For example, U.S. Patent Application Publication No. 2011/0049050, the disclosure of which is incorporated by reference herein, describes an arrangement in which a raw water pump is controlled in response to a flow rate measurement of the raw water between the raw water pump and a reverse osmosis element, and in which a control valve within a concentrate conduit may be controlled in response to a flow measurement provided by a flow meter in the concentrate conduit. Application of these techniques to the  FIG. 1  arrangement would include controlling pump  124  in response to a flow measurement of input  131  and controlling restrictor  142  in response to a flow measurement of output  141 . 
         [0020]    International Patent Application Publication No. WO  96 / 41675 , the disclosure of which is incorporated by reference herein, describes an arrangement in which the flow of concentrate is automatically adapted to the flow of raw water so as to maintain a constant ratio between the flow of concentrate and the flow of raw water and/or a constant ratio between the flow of permeate and the flow of concentrate. The flow of raw water is detected by a flow meter disposed upstream of the pump which provides for the filter pressure and is used to control the flow cross-section and flow resistance in the concentrate outlet conduit. Application of these techniques to the  FIG. 1  arrangement would include controlling restrictor  142  in response to a flow measurement of input  131 . 
         [0021]    U.S. Pat. No. 4,626,346, the disclosure of which is incorporated by reference herein, describes an arrangement which includes a pressure sensing switch means coupled to sense the pressure in a water storage compartment. When the sensed pressure increases to a point above a predetermined value, the pressure sensing switch means opens a switch thereby interrupting operation of the reverse osmosis system. The inventors have noted that this arrangement, would be unable to provide any control finer-grained than so-called “bang-bang” (i.e., on-off) control. 
         [0022]    Moreover, Aquatec International Inc. of Irvine, Calif., USA (hereinafter “Aquatec”) sells variable speed delivery/demand pumps (e.g., DDP series models 55X and 58XX) which vary their speed based on the pressure associated with their outputs (e.g., a pump located within distributor  158  of  FIG. 1  which changes its speed based on a pressure associated with its output), but these variable-speed pumps are not suitable for use as either feed pumps (e.g., pump  124  in  FIG. 1 ) or as permeate pumps (e.g., pump  152  in  FIG. 1 ). Instead, Aquatec sells feed pumps (e.g., CDP series models 68XX and 88XX) which do not offer variable speed, but rather only allow for “bang-bang” (i.e., on-off) control using components such as pressure switches (e.g., PSW series), vacuum switches (e.g., VSW series), tank level controllers (e.g., TLC series) and/or electronic shut-off valves (e.g., ESO series). Likewise, Aquatec&#39;s permeate pumps (e.g., ERP-1000) only allow for “bang-bang” (i.e., on-off) control using hydraulic shut-off valves (e.g., ASV series). Literature describing the aforementioned products commercially available from Aquatec is submitted herewith and incorporated by reference herein. Such arrangements which would involve controlling valve  122  and/or pump  124  responsive to pressure in output  155  and/or tank  156 . 
         [0023]    Some conventional reverse osmosis systems, such as those commercially available from Water Tec of Tuscon (Ariz., USA) and described in the Instruction Manual submitted herewith and incorporated by reference herein, include pressure gauges which display the pressure currently present at various points within the reverse osmosis system. The inventor has noted that these conventional arrangements fail to provide monitoring of differences between pressures at various points within the system (e.g., the difference between input pressure and output pressure) and/or variations in pressure over time (e.g., increasing or decreasing pressure), both of which can be important indicators of conditions within the filter. Moreover, the inventor has noted that these conventional arrangements require a user to manually monitor the gauges and manually make adjustments to the operation of the filter responsive to the pressure measurements displayed by the gauges. 
         [0024]    There is a long-felt need for an arrangement which provides more effective monitoring and adjustment of operational conditions within a reverse osmosis system or other filtration system in order to ensure optimal operation. In particular, there is a long-felt need for an arrangement which provides improved pressure monitoring and/or pump speed control in such a system. 
       SUMMARY OF THE INVENTION 
       [0025]    It is to be understood that both the general and detailed descriptions that follow are exemplary and explanatory only and are not restrictive of the invention. 
       DISCLOSURE OF INVENTION 
       [0026]    A first object of the invention is to provide for more effective monitoring of conditions within a filtration system. This object may be accomplished at least in part by measuring a pressure of a given input of the filtration system, measuring a pressure of a given output of the filtration system, and generating a signal indicative of a difference between the pressure of the given input of the filtration system and the pressure of the given output of the filtration system. 
         [0027]    The signal may be transmitted over at least one of a wired and a wireless connection to facilitate remote monitoring of the fluid processing system. Multiple values of the signal may be recorded at differing times on a storage medium to facilitate detection of variations in the signal. 
         [0028]    In one embodiment in which the filtration system comprises a reverse osmosis filter, the signal may be indicative of the difference between the pressure of an input of the reverse osmosis filter and the pressure of the permeate output of the reverse osmosis filter. In another embodiment in which the filtration system comprises at least one pretreatment filter within a reverse osmosis system, the given output of the fluid processing system may be coupled to an input of a reverse osmosis filter within the reverse osmosis system. 
         [0029]    A second object of the invention is to provide for more accurate adjustment of pressure and pump speed within a reverse osmosis system comprising a feed input, a concentrate output, and a permeate output. In some embodiments, this object is accomplished at least in part by adjusting a speed of at least a first pumping mechanism based at least in part on pressure of the permeate output of the reverse osmosis system. 
         [0030]    In other embodiments, this object is accomplished at least in part by adjusting a speed of at least a first pumping mechanism based at least in part on a signal indicative of a difference between a pressure of the feed input of the reverse osmosis system and a pressure of the permeate output of the reverse osmosis system. The speed of at least the first pumping mechanism may adjusted so as to maintain the difference between the pressure of at least the feed of the reverse osmosis system and the pressure of at least the permeate output of the reverse osmosis system at a substantially constant level. 
         [0031]    Adjusting the speed of the first pumping mechanism may include increasing or decreasing the speed of the first pumping mechanism from a first non-zero value to a second non-zero value without enabling or disabling the first pumping mechanism. The speed of at least the first pumping mechanism may be adjusted so as to at least partially compensate for variations in a pressure of the feed input of the reverse osmosis system. 
         [0032]    The speed of the at least first pumping mechanism may be adjusted so as to maintain the pressure of the permeate output of the reverse osmosis system at a substantially constant level. For example, the pressure of the permeate output of the reverse osmosis system may be maintained within a range of approximately 3 pounds per square inch (psi) and 5 psi. 
         [0033]    The present invention seeks to overcome or at least ameliorate one or more of several problems, by providing more effective monitoring of conditions (e.g., filter performance) within, and/or more accurate adjustment of feed pressure within, a reverse osmosis system in order to ensure optimal operation. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0034]    The accompanying figures further illustrate the present invention. 
         BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0035]      FIG. 1  is a block diagram depicting a reverse osmosis system according to the prior art. 
           [0036]      FIG. 2  is a block diagram depicting a reverse osmosis system according to a first illustrative embodiment of the present invention. 
           [0037]      FIG. 3  is a block diagram depicting a reverse osmosis system according to a second illustrative embodiment of the present invention. 
           [0038]      FIG. 4  is a block diagram depicting a reverse osmosis system according to a third illustrative embodiment of the present invention. 
           [0039]      FIG. 5  is a block diagram depicting a reverse osmosis system according to a fourth illustrative embodiment of the present invention. 
       
    
    
     LIST OF REFERENCE NUMBERS FOR THE MAJOR ELEMENTS IN THE DRAWING 
       [0040]    The following is a list of the major elements in the drawings in numerical order.
         101  input (of pretreatment assembly  110 )     110  pretreatment assembly     111  sediment filter (within pretreatment assembly  110 )     112  first carbon filter (within pretreatment assembly  110 )     113  second carbon filter (within pretreatment assembly  110 )     121  output (of pretreatment assembly  110 )     122  electro valve     123  input (of feed pump  124 )     124  feed pump     130  reverse osmosis (RO) filter     131  input (of RO filter  130 )     132  region of high solute concentration (within RO filter  130 )     133  semipermeable membrane (within RO filter  130 )     134  region of low solute concentration (within RO filter  130 )     141  concentrate output (of RO filter  130 )     142  restrictor (for concentrate outlet  141 )     143  concentrate storage tank     151  permeate output (of RO filter  130 )     152  permeate pump     153  output (of permeate pump  152 )     154  check valve     155  input of permeate storage tank  156       156  permeate storage tank     157  output of permeate storage tank  157       158  permeate distributor     261  pressure sensor (for permeate output  151 )     262  pressure signal (from pressure sensor  261 )     267  control logic (for permeate pressure signal  262 )     268  pump speed control signal (for feed pump  124 )     269  pump speed control signal (for permeate pump  152 )     372  pressure sensor (for RO filter input  131 )     373  pressure signal (from pressure sensor  372 )     374  pressure signal (from pressure sensor  261 )     375  control logic (for pressure signals  373  and  374 )     376  differential pressure signal (for pressure signals  373  and  374 )     487  control logic (for differential pressure signal  376 )     488  control signal (for feed pump  124 )     489  control signal (for permeate pump  152 )     591  pressure sensor (for input  101  of pretreatment assembly  110 )     592  pressure sensor (for output  121  of pretreatment assembly  110 )     593  pressure signal (from pressure sensor  591 )     594  pressure signal (from pressure sensor  592 )     595  control logic (for pressure signals  593  and  594 )     596  differential pressure signal (for pressure signals  593  and  594 )       
 
       DETAILED DESCRIPTION OF THE INVENTION 
     Mode(s) for Carrying Out the Invention 
       [0085]    The preferred embodiment of the present invention is described herein in the context of water filtration using a reverse osmosis system, but is not limited thereto, except as may be set forth expressly in the appended claims. For example, Although the preferred embodiments of the present invention are described herein in the context of water filtration, one skilled in the art would understand that other fluids may be used, such as wine or milk. 
         [0086]      FIG. 2  is a block diagram depicting a reverse osmosis system according to a first illustrative embodiment of the present invention.  FIG. 2  includes most of the components discussed hereinabove with reference to  FIG. 1 , and these components function in a similar manner within the  FIG. 2  embodiment as in the  FIG. 1  embodiment. However,  FIG. 2  includes additional components which are not present within the  FIG. 1  embodiment. 
         [0087]    In the  FIG. 2  embodiment, pretreatment assembly  110  comprises sediment filter  211  and activated carbon filters  212  and  213 . It is important to note that this arrangement is exemplary. Depending on the composition of the input  101  and/or the configuration of the filter  130 , the pretreatment assembly  110  could include differing numbers, types and/or orderings of components. For example, the pretreatment assembly  110  could include equipment for hollow fiber microfiltration, capillary ultrafiltration, gravity filtration, lime clarification, flocculation and/or coagulation in addition to or instead of sediment filter  211  and/or activated carbon filters  212  and  213 . 
         [0088]    Sediment filter  211  may be included in order to trap particles, which may include, but need not be limited to, rust and/or calcium carbonate. Other embodiments may omit sediment filter  211 , while still other embodiments may include additional sediment filters with equal and/or decreasing pore sizes (e.g., decreasing from 5 μm to 1 μm). In one embodiment, a single string-wound polypropylene filter may be used with pores of approximately 1 μm. 
         [0089]    Activated carbon filters  212  and  213  may be included in order to trap, for example, organic chemicals and/or chlorine. In one embodiment, activated carbon filters  212  and  213  may be capable of removing particles of approximately 5 μm. In other embodiments, activated carbon filters  212  and  213  may be configured to remove particles of other sizes (e.g., decreasing from 50 μm to 0.5 μm). In some embodiments, including but not limited to those in which membrane  133  within RO filter  130  is formed from cellulose acetate rather than a thin film composite, activated carbon filters  212  and  213  may be omitted, or activated carbon filters  112  and  113  may be included after, rather than before, RO filter  130 . 
         [0090]    In a reverse osmosis system, there is an inverse relationship between pump speed (e.g., the speed of feed pump  124  and/or permeate pump  152 ) and the pressure of permeate output  151 : as pump speed decreases, permeate output pressure increases. There is also an inverse relationship between the pressure of permeate output  151  and the efficiency of RO filter  130 , hence the efficiency of RO filter  130  could often be enhanced by maintaining a substantially constant pressure within permeate output  151 , for example, a pressure of approximately 3 to 5 psi. 
         [0091]    In the  FIG. 2  embodiment, permeate output  151  is coupled to a pressure sensor  261  which may be, for example, an analog pressure sensor. Many types of pressure sensors, including but not limited to pressure transducers and/or pressure transmitters, may be used in connection with embodiments of the present invention. Pressure sensor  261  generates a signal  262  indicative of the pressure within permeate output  151 . In some embodiments, signal  262  may comprise an electrical signal having a voltage, current, and/or frequency which varies in direct and/or indirect proportion to the pressure within permeate output  151 . 
         [0092]    Signal  262  may be coupled to control logic  267 , which generates feed pump control signal  268  and permeate pump control signal  269  based on signal  262 . Pump control signals  268  and  269  are respectively coupled to, and operative to control the speeds of, feed pump  124  and permeate pump  152 . 
         [0093]    In one embodiment, feed pump  124  and/or permeate pump  152  may be driven by one or more electric motor units, and at least one of the one or more electric motor units has at least one variable speed drive (VSD) incorporated therein. Feed pump  124  and permeate pump  152  may each be driven by a respective electric motor, or they may be driven by a common electric motor (either with a respective VSD for each pump or with a common VSD for both pumps). 
         [0094]    In a preferred embodiment, pressure sensor  261  and control logic  267  implement a closed control loop which controls (e.g., servos) the speeds of pumps  124  and/or  152  in order to maintain a substantially constant pressure within permeate output  151 , for example, a pressure of approximately 3 to 5 psi. Adjusting the speeds of pumps  124  and/or  152  based on pressure within permeate output  151  using a closed control loop is preferable to maintaining a constant pump speed because the closed control loop is better able to account for pressure variations within permeate output  151  caused by, for example, pressure variations within inputs  131  and/or  101 . 
         [0095]    Although the  FIG. 2  embodiment shows control logic  267  generating two control signals  268  and  269 , thereby controlling the speed of both pumps  124  and  152 , other embodiments may omit one of these control signals and thereby control the speed of only a single pump. Furthermore, although the  FIG. 2  embodiment shows control logic  267  which generates pump control signals  268  and  269  from a pressure signal  262  generated by pressure sensor  261 , other arrangements fall within the scope of the present invention. For example, pressure sensor  261  could be operative to directly generate pump control signals  268  and/or  269  (e.g., by having control logic  267  incorporated therein), or pumps  124  and/or  152  could operate directly on pressure signal  262  (e.g., by having control logic  267  incorporated therein). 
         [0096]      FIG. 3  is a block diagram depicting a reverse osmosis system according to a second illustrative embodiment of the present invention. As with  FIG. 2 ,  FIG. 3  includes most of the components discussed hereinabove with reference to  FIG. 1 . These components function in a similar manner within the  FIG. 3  embodiment as in the  FIG. 1  embodiment. 
         [0097]      FIG. 3 , like  FIG. 2 , includes a pressure sensor  261  coupled to permeate output  151  of RO filter  130 . However,  FIG. 3  also includes a pressure sensor  372  coupled to input  131  of RO filter  130 . In some embodiments, at least one of pressure sensor  261  and pressure sensor  372  may comprise an analog pressure sensor. Rather than generating signal  262  for transmission to control logic  267  (as in  FIG. 2 ), pressure sensor  261  generates a signal  374  for transmission to control logic  375 . Likewise, pressure sensor  372  generates a signal  373  for transmission to control logic  375 . 
         [0098]    Signal  373  is indicative of the pressure in input  131  of RO filter  130 , and signal  374  is indicative of the pressure in permeate output  151  of RO filter  130 . In some embodiments, signals  373  and/or  374  may comprise electrical signals having a voltage, current, and/or frequency which varies in direct and/or indirect proportion to the pressure of input  131  and/or permeate output  151 , respectively. Control logic  375  generates a signal  376 , which is indicative of the difference between signal  373  and signal  374 . Hence, signal  376  is indicative of the difference between the pressure in input  131  of RO filter  130  and the pressure in permeate output  151  of RO filter  130 . 
         [0099]    This pressure difference may be indicative of the condition of membrane  133  within RO filter  130 . For example, the pores within membrane  133  may become clogged over time as the RO filter is used (a condition commonly referred to as “fouling” or “scaling”). This will result in an increased difference between the pressure of input  131  and the pressure of permeate output  151  because of the greater resistance provided by membrane  133  to the solvent. Fouling or scaling may result in decreased performance of the RO filter  130  (e.g., a given quantity of feed resulting in production of more concentrate and less permeate). An increased difference between the pressure of input  131  and the pressure of permeate output  151  will also increase the pressure which must be provided at input  131  to maintain a constant pressure at permeate output  151  and therefore can increase the energy requirements for, and decrease the energy efficiency of, RO filter  130 . 
         [0100]    Signal  376  may be output to allow a user to monitor the condition of RO filter  130 , such as to indicate whether it is necessary to clean and/or replace membrane  133  (e.g., due to excessive “fouling” or “scaling”). For example, signal  376  could be coupled to a display mechanism, such as one or more light-emitting diodes (LEDs) capable of providing a binary indication (e.g., a light which either turns on or changes color responsive to the pressure difference exceeding a predetermined threshold) and/or a numeric display of the pressure difference. Additionally or alternatively, signal  376  could be transmitted over a wired or wireless network connection to facilitate remote monitoring of the RO filter  130 . Additionally or alternatively, the value of signal  376  could be periodically and/or continuously recorded on a computer-readable storage medium (locally and/or remotely) to track changes over time. 
         [0101]    Although  FIG. 3  shows an arrangement in which signal  376  is generated by control logic  375  based on respective signals  373  and  374  generated by two pressure transducers  372  and  261 , other arrangements fall within the scope of the invention. For example, signal  376  could be generated using a single differential pressure transducer having inputs respectively coupled to input  131  and permeate output  151 . Signal  376  may comprise an electrical signal having a voltage, current and/or frequency which varies in direct and/or indirect proportion to the difference in the pressure of input  131  and the pressure of permeate output  151 . 
         [0102]      FIG. 4  is a block diagram depicting a reverse osmosis system according to a third illustrative embodiment of the present invention.  FIG. 4  includes the components discussed hereinabove with reference to  FIG. 3 . These components function in a similar manner within the  FIG. 4  embodiment as in the  FIG. 3  embodiment. 
         [0103]    However, in the  FIG. 4  embodiment, signal  376  is input to control logic  477 , which generates control signals  478  and  479  to control the speeds of feed pump  124  and permeate pump  152 , respectively. In a preferred embodiment, pressure transducers  372  and  261  and control logic  375  and  477  implement a closed control loop which controls (e.g., servos) the speeds of pumps  124  and/or  152  so as to maintain a substantially constant difference in pressure between input  131  and output  151  of RO filter  130  (e.g., to attempt to hold pressure substantially constant across RO filter  130 ). Adjusting the speeds of pumps  124  and/or  152  based on the difference in pressure between input  131  and permeate output  151  using a closed control loop is preferable to merely maintaining a constant pump speed because the closed control loop is better able to account for pressure variations within permeate output  151  caused by, for example, pressure variations within inputs  131  and/or  101 . 
         [0104]    Although the  FIG. 4  embodiment shows control logic  477  generating two control signals  478  and  479 , thereby controlling the speed of both pumps  124  and  152 , other embodiments may omit one of these control signals and thereby control the speed of only a single pump. Moreover, although  FIG. 4  shows an arrangement in which signal  376  is generated by control logic  375  based on respective signals  373  and  374  generated by two pressure sensors  372  and  261 , other arrangements fall within the scope of the invention. For example, signal  376  could be generated using a single differential pressure transducer having inputs respectively coupled to input  131  and output  151 . Other embodiments could combine the functionalities of control logic  375  and control logic  377  within a single control logic unit operative to receive to generate one or more pump control signals  478  and  479  based directly on pressure signals  373  and  374 , rather than generating and/or utilizing signal  376 . 
         [0105]      FIG. 5  is a block diagram depicting a reverse osmosis system according to a fourth illustrative embodiment of the present invention. As with  FIG. 2 ,  FIG. 5  includes most of the components discussed hereinabove with reference to  FIG. 1 . These components function in a similar manner within the  FIG. 5  embodiment as in the  FIG. 1  embodiment 
         [0106]    The  FIG. 5  embodiment includes a first pressure sensor  591  coupled to input  101  of pretreatment assembly  110  and a second pressure sensor  592  coupled to output  121  of pretreatment assembly  110 . Pressure sensor  591  generates signal  593 , which is indicative of the pressure in input  101  of pretreatment assembly  110  and pressure sensor  592  generates signal  594 , which is indicative of the pressure in output  121  of pretreatment assembly  110 . 
         [0107]    Control logic  595  receives signals  593  and  594  from pressure transducers  591  and  592 , respectively, and generates a signal  596 , which is indicative of the difference between signal  593  and signal  594 . Hence, signal  596  is indicative of the difference between the pressure in input  101  of pretreatment assembly  110  and the pressure in permeate output  121  of pretreatment assembly  110 . This pressure difference is indicative of conditions within the pretreatment assembly  110 . 
         [0108]    In particular, the pressure difference may be indicative of the condition of one or more components (e.g., filters  211 ,  212  and/or  213 ) within pretreatment assembly  110 . For example, in a manner similar to that discussed with reference to RO filter  130 , pores within sediment filter  211  may become clogged as sediment filter  211  is used (a condition commonly referred to as “fouling” or “scaling”). This will result in an increase in the difference between pressure in input  101  and pressure in output  121 , as well as reduced efficiency of sediment filter  211  and pretreatment assembly  110 . 
         [0109]    Signal  596  may be output to allow a user to monitor the condition of pretreatment assembly  110 , and more particularly to indicate whether it is necessary to repair and/or replace component(s) within pretreatment assembly  110 . For example, signal  596  could be coupled to a display mechanism, such as one or more light-emitting diodes (LEDs) capable of providing a binary indication (e.g., a light which either turns on or changes color responsive to the pressure difference exceeding a predetermined threshold) and/or a numeric display of the pressure difference. Additionally or alternatively, signal  596  could be transmitted over a wired or wireless network connection to facilitate remote monitoring of pretreatment assembly  110 . Additionally or alternatively, the value of signal  596  could be periodically and/or continuously recorded on a computer-readable storage medium (locally and/or remotely) to track changes over time. 
         [0110]    Although  FIG. 5  shows an arrangement in which signal  596  is generated by control logic  595  based on respective signals  593  and  594  generated by two pressure transducers  591  and  592 , other arrangements fall within the scope of the invention. For example, signal  596  could be generated using a single differential pressure transducer having inputs respectively coupled to input  101  and output  121 . 
         [0111]    Finally, those skilled in the art will appreciate that features of the  FIGS. 2-5  embodiments may be combined with each other, and moreover that the present invention can be applied to many types of filtration or other fluid processing systems in addition to reverse osmosis systems. 
       INDUSTRIAL APPLICABILITY 
       [0112]    To solve the aforementioned problems, the present invention is a unique system which provides more effective monitoring and adjustment of operational conditions within a reverse osmosis system or other filtration system. 
       Alternate Embodiments 
       [0113]    Alternate embodiments may be devised without departing from the spirit or the scope of the invention. For example, the inventive device could be adapted to many types of fluid processing systems in addition to the reverse osmosis filtration systems described herein.