LIFE OF THE SAME

Field of the invention

The invention relates to a water treatment system and method for predicting remaining filter life of the same. More particularly, the invention relates to how life of filter in a water treatment system can be predicted and communicated to a user.

Background of the invention

Water treatment systems comprise of one of more of different type of filters and prefilter is the one that is usually upstream of the main filter such as a reverse osmosis filter membrane or a microfilter or an ultrafiltration membrane.

These filters usually have a limited life and need to be changed after their life is over. Their life is dependent on a variety of factors such as input water quality, usage of the filter over a period of time, volume of water dispensed through the water treatment device.

Mostly, the filter life of prefilters is predicted basis an assumption of water dispensed through the water treatment device, or device running hours, however these are not basis for accurate assumption as they do not take into account other factors such as input water quality which may change over a period of time, performance and life of other filters, which may affect the output of treated water.

The filter life can be predicted basis an average volume of water at which the prefilter is known to require replacement. That is ‘X’ volumes of water dispensed by the water treatment device/ average volume of water at which the prefilter is known to require replacement. However, this is not the most accurate way of predicting prefilter life and neither is dynamic to take into account the realtime changes in the quality of water. And also, there is a likelihood of change in input quality of water over a period of time, which is not taken into account in these systems. JP4228410 (TOTO LTD.) discloses a water treatment apparatus for generating hypochlorous acid by electrolyzing an aqueous solution supplied from a water supply source after mixing a saline solution with a water supply source and then passing it through a filter. The document also mentions about providing advanced filter replacement notice. However, the document does not state about predicting and reporting end of life of a pre-filter in specific. Also, the document is not capable of predicting the life of a pre-filter in a basic water treatment system as the flow sensor is positioned upstream and has a mixing pot in its low path and therefore is not capable of detecting flow rate of water entering the filter and does not provide any information about the filter, and therefore is not capable of predicting filter life independently.

Therefore, there is a need to predict prefilter life in a basic water treatment system without adding any additional components for filter life prediction, through a more accurate means and which is more dynamic to take into account the realtime changes in the quality of water, and change in input quality of water over a period of time.

Summary of the invention

First aspect of the present invention provides a system for predicting prefilter life, the system comprising:

A. a water treatment device comprising,

i. an inlet;

ii. a prefilter downstream of the inlet;

iii. a water treatment unit further downstream of the prefilter;

iv. a flow sensor positioned downstream of the water treatment unit;

v. an outlet for dispensing treated water; and

B. a control module, capable of,

i. storing data generated by the flow sensor;

ii. storing a value of volume dispensed (V _n ) from the water treatment device at a given time since the last incident of change or installation of prefilter; iii. storing incidents of change of prefilter; wherein, the control module is configured to: a) record values of flowrate (FR _n ) sensed by the flow sensor, wherein FR _n is a direct function of the water treatment system performance; b) plot a graph of FR _n values against V _n values;

c) store a predetermined value of flow rate FR _min ; wherein FR _min is a value of FR _n , a value less than FR _min indicates end of prefilter life. d) extrapolate the graph to deduce V _n at (FR _min ), the deduced value of V _n at FR _min is the estimated volume (VE) indicating prefilter life.

Second aspect of the present invention provides a method of method of predicting prefilter life, the method comprising steps of: i. providing the system according to the first aspect;

ii. recording values of V _n ;

iii. recording values of flowrate (FR _n ) sensed by the flow sensor, wherein FR _n is a direct function of the prefilter performance;

iv. plotting a graph of FR _n values against V _n values;

v. storing a predetermined value of flow rate FR _min ; wherein FR _min is the minimum value of FR _n , a value less than FR _min indicates end of prefilter life; and

vi. extrapolating the graph to deduce V _n at (FR _min ), the deduced value of V _n at FR _min is the estimated volume (VE) indicating prefilter life.

It should be understood that the present invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being implemented in various ways.

The terms“including”,“comprising”,“containing” or“having” and variations thereof as used herein are meant to encompass the items listed thereafter as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and“coupled” and variations thereof are used broadly and encompass direct and indirect mountings, connections, supports, and couplings. The description below are intended to clarify the invention and are not intended to limit the invention to those examples per se. Similarly, all percentages are weight/weight percentages unless otherwise indicated.

Except in the operating and comparative examples, or where otherwise explicitly indicated, all numbers in this description indicating amounts of material or conditions of reaction, physical properties of materials and/or use are to be understood as modified by the word "about".

Numerical ranges expressed in the format "from x to y" are understood to include x and y. When for a specific feature multiple preferred ranges are described in the format "from x to y", it is understood that all ranges combining the different endpoints are also contemplated.

The phrase ‘direct function of the membrane filter performance’ throughout the specification means as the value which is a direct function increases, it indicates good performance of membrane and as the value decreases, indicates poor membrane filter performance.

The phrase ‘inverse function of the membrane filter performance’ throughout the specification means as the value which is an inverse function increases, it indicates poor performance of membrane and as the value decreases, indicates good membrane filter performance.

Detailed description of the invention

The present invention relates to a system for predicting prefilter life, the system comprising a water treatment device and a control module, wherein, the control module is configured to: record values of flowrate (FR _n ) sensed by the flow sensor, wherein FR _n is a direct function of the water treatment system performance; plot a graph of FR _n values against V _n values; store a predetermined value of flow rate FR _min ; wherein FR _min is a value of FR _n , a value less than FR _min indicates end of prefilter life; and extrapolate the graph to deduce V _n at (FR _min ), the deduced value of V _n at FR _min is the estimated volume (VE) indicating prefilter life. Throughout the description, it shall be understood that for the purposes of the present invention, the term ‘communication’ shall mean to include both direct or indirect communication, wired or wireless communication, electrical or non-electric communication, though waves, radiations and all kinds of communication used as known in the art.

This system and method helps in most accurate way of predicted prefilter life as opposed to the existing ways where the prefilter life is based on the collated average data of performance of a prefilter based on lab results. Where, the filter life can be predicted basis an average volume of water at which the prefilter is known to require replacement. That is‘X’ volumes of water dispensed by the water treatment device/ average volume of water at which the prefilter is known to require replacement. However, this is not the most accurate way of predicting prefilter life and neither is dynamic to take into account the realtime changes in the quality of water. And also, there is a likelihood of change in input quality of water over a period of time, which is not taken into account in these systems.

The present invention finds a solution to predict life and report end of life of a pre-filter in a basic water treatment system. It is only during normal functioning of a basic water purification device, that the inventors of the present invention set to find a way to predict the pre-filter life, without having to add any additional components and without adding any additional costs of the basic water treatment device

Further, the inventors realized that a pre-filter is different from other filters, if present, of a water treatment system. This is because it is the first to face the raw water supply which could be from varied sources and most often than not having larger size particles which the pre-filter removes, so there is a high likelihood that there is sudden clogging of the pre-filter or clogging happens over a period of time. And for this reason, the inventors set to find a specific solution to this specific problem.

The present invention provides a system for predicting prefilter life, the system comprising:

A. a water treatment device comprising, i. an inlet;

ii. a prefilter downstream of the inlet;

iii. a water treatment unit further downstream of the prefilter;

iv. a flow sensor positioned downstream of the water treatment unit;

v. an outlet for dispensing treated water; and

B. a control module, capable of,

i. storing data generated by the flow sensor;

ii. storing a value of volume dispensed (V _n ) from the water treatment device at a given time since the last incident of change or installation of prefilter; iii. storing incidents of change of prefilter; wherein, the control module is configured to: a) record values of flowrate (FR _n ) sensed by the flow sensor, wherein FR _n is a direct function of the water treatment system performance; b) plot a graph of FR _n values against V _n values;

c) store a predetermined value of flow rate FR _min ; wherein FR _min is a value of FR _n , a value less than FR _min indicates end of prefilter life; and d) extrapolate the graph to deduce V _n at (FR _min ), the deduced value of V _n at FR _min is the estimated volume (VE) indicating prefilter life.

It is preferred that the water treatment device is preferably a water purifying device having one or more filters and a prefilter is preferably positioned upstream of the water treatment unit and is preferably the first filter to come in contact with the input or raw water

It is preferred that in the system of the present invention, the control module is a part of the water treatment device or is a part of remotely located server and preferably when the control module is a part of remotely located server, the control module comprises a communication module.

It is preferred that in the system of the present invention, the system further comprises a display device and the display device is preferably a part of water treatment device or control module or is an is an independent portable device. It is preferred that in the system of the present invention, further comprises a communication module when other components of the system, control module and/or display device are not electrically connected to the water treatment device.

It is preferred that in the system of the present invention, the water treatment device further comprises a pressure sensing unit upstream of the water treatment unit and preferably the communication module is further capable of storing data from the pressure sensing unit and incidents Έ’ when the pressure sensing unit detects pressure less than a predetermined value of pressure P _m in.

It is preferred that in the system of the present invention, when the pressure sensing unit is positioned downstream of the prefilter, the control module is further configured to report that prefilter life is over if the Έ’ is reported for at least‘t’ number of times within a predetermined value of volume dispensed through the water treatment unit.

Water Treatment device

The water treatment device of the present invention comprises:

i. an inlet;

ii. a prefilter downstream of the inlet;

iii. a water treatment unit further downstream of the prefilter;

iv. a flow sensor positioned downstream of the water treatment unit;

v. an outlet for dispensing treated water; and

It is preferred that the water treatment device of the present invention is a water purifying device, wherein an inlet is provided for entry of raw/untreated water and a prefilter is provided downstream of the inlet and in fluid communication with the inlet.

Prefilter:

It is preferred that the prefilter is the first filter or stage of water purification and more preferred that the prefilter is intended to remove particulate matter from the water. It is more preferred that the prefilter is a sediment filter. If the prefilter is not the first stage of water purification then, it at least precedes main stages of filtration in the water purification process.

Water treatment unit:

Water treatment unit is the main filtration unit in fluid communication with the prefilter and can be a RO membrane, microfiltration membrane, Ultrafiltration membrane or any other filtration unit.

Flow Sensor:

Flow sensor measures the water flow. It is preferred that the Flow sensor is placed in the flow path of the treated water from the water treatment unit which permits measurement of water being dispensed out of the system. The FS preferably gives input pulses to either the control module and more preferably when the control module is a part of the water treatment device or a control circuit within the water treatment device. The control module or the control circuit is able to measure flow rate based on input from flow sensor and calculates the quantity of water passing through it.

Control Circuit:

The water treatment device of the present invention preferably comprises a control circuit, which could be a part of the control module, when control module is a part of the water treatment device or could be an independent controlling unit of the water treatment device.

When the control circuit is an independent controlling unit of the water treatment device, it preferably comprises a micro-computer unit (MCU) and a communication module adapted to communicate with the control module and send information with respect to flow sensor data etc. It is preferred that the micro-computer unit (MCU) of the control circuit unit and is responsible for the logical control of the device. The MCU forms the seat of control circuit intelligence. The control circuit of the water treatment device is capable of:

i. storing data generated by the flow sensor;

ii. storing a value of volume dispensed (V _n ) from the water treatment device at a given time since the last incident of change or installation of prefilter; and

iii. storing incidents of change of prefilter; and may be configured to: a) record values of flowrate (FR _n ) sensed by the flow sensor, wherein FR _n is a direct function of the water treatment system performance; b) plot a graph of FR _n values against V _n values;

c) store a predetermined value of flow rate FR _min ; wherein FR _min is a value of FR _n , a value less than FR _min indicates end of prefilter life. d) extrapolate the graph to deduce V _n at (FR _min ), the deduced value of V _n at FR _min is the estimated volume (VE) indicating prefilter life.

The control circuit is also capable of storing data from the pressure sensing unit, when present; and incidents Έ’ when the pressure sensing unit detects pressure less than a predetermined value of pressure P _min .

It is preferable that when the pressure sensing unit is positioned downstream of the prefilter, the control circuit is further capable of being configured to report that prefilter life is over if the Έ’ is reported for at least‘t’ number of times within a predetermined value of volume dispensed through the water treatment unit.

The control circuit may further be configured to send alerts to change the prefilter. Sending of alerts may be via the display device or any other medium.

The control circuit is preferably capable of being configured to send alerts in advance of the end of prefilter life, for example at 80% of the VE, or any such value may be picked which gives sufficient time to change the prefilter before its life is over. Communication module

It is preferred that the water treatment device of the present invention comprises a communication module, which is a part of control module or control circuit when present in the water treatment device or is an independent unit.

The communication module of the present invention is preferable a part of the control circuit or the communication module, however it is capable of functioning as an independent unit connected to the control circuit or the control module when present in the device. The communication module is responsible for data communication between the device and the control module when the control module is not a part of the device. The communication module could also be configured to communicate with any other external device such as portable devices such as a phone, laptop, a display device and the likes.

The communication module is preferably electrically or electronically connected to the control circuit of the device.

When the control module is outside the device, the communication module preferably establishes wireless connection with the control module. The communication module is also capable of establishing a connection with an electronic or electrical communication device when configured in a suitable manner. It is highly preferred that the communication module is preferably configured to establish a wireless connection with a communication device such as a phone or a computer.

The communication module most preferably comprises at least one integrated circuit for establishing the connection between the device and the control module or any other external device as the case may be. It is highly preferred to use a GSM/CDMA/WCDMA/LTE and the like technology based wireless network to communicate data by the communication module. Pressure Sensing Unit (LPS)

It is preferred that the device comprises a pressure sensing unit which is preferably a Low-pressure Sensor (LPS) for sensing the input water pressure and communicating the status to the control circuit or the control module. It also functions as a switch. LPS is preferably related to the input pressure of water. An LPS is configured to switch off and report an error Έ’ when the pressure sensing unit detects pressure less than a predetermined value of pressure P _min. When water is not present at the input side or pressure is low, the LPS switch will be OFF and Έ’ will be reported. If water is present with required pressure at the input then the LPS switch will be ON. If the Έ’ is reported for at least‘t’ number of times within a predetermined value of volume dispensed through the water treatment unit, the control module is further configured to report that prefilter life is over.

Control Module

A control module of the present invention is capable of:

i. storing data generated by the flow sensor;

ii. storing a value of volume dispensed (V _n ) from the water treatment device at a given time since the last incident of change or installation of prefilter; and

iii. storing incidents of change of prefilter; and is configured to: a) record values of flowrate (FR _n ) sensed by the flow sensor, wherein FR _n is a direct function of the water treatment system performance; b) plot a graph of FR _n values against V _n values;

c) store a predetermined value of flow rate FR _min ; wherein FR _min is a value of FR _n , a value less than FR _min indicates end of prefilter life. d) extrapolate the graph to deduce V _n at (FR _min ), the deduced value of V _n at FR _min is the estimated volume (VE) indicating prefilter life. The control module could be a part of the water treatment device or could be a part of a remotely located server and when the control module is a part of remotely located server, the control module preferably comprises a communication module.

It is preferable that the communication module is further capable of storing data from the pressure sensing unit, when present; and incidents Έ’ when the pressure sensing unit detects pressure less than a predetermined value of pressure P _m in.

It is preferable that when the pressure sensing unit is positioned downstream of the prefilter, the control module is further configured to report that prefilter life is over if the Έ’ is reported for at least‘t’ number of times within a predetermined value of volume dispensed through the water treatment unit.

The control module may further be configured to send alerts to change the prefilter. Sending of alerts may be via the display device or any other medium.

The control circuit may preferably be configured to send alerts in advance of the end of prefilter life, for example at 80% of the VE, or any such value may be picked which gives sufficient time to change the prefilter before its life is over.

Server

It is preferable that the water treatment device of the present invention is in communication with a server, preferably a remotely located server and preferably through a wireless medium such as internet.

The server may also comprise the control module of the present invention.

A server according to the present invention may be a computer program or a device that provides functionality for other programs or devices.

It is also preferable that server communicates with other external device such as portable devices such as a phone, laptop, a display device and the likes. The server of the present invention may be accessed over a network such as a WAN or LAN or GPRS or the likes.

The term‘remotely located’ for the purposes of the present invention in the context of server means connected through wireless means.

The server of the water treatment device is capable of:

iv. storing data generated by the flow sensor;

v. storing a value of volume dispensed (V _n ) from the water treatment device at a given time since the last incident of change or installation of prefilter; and

vi. storing incidents of change of prefilter; and may be configured to: e) record values of flowrate (FR _n ) sensed by the flow sensor, wherein FR _n is a direct function of the water treatment system performance; f) plot a graph of FR _n values against V _n values;

g) store a predetermined value of flow rate FR _min ; wherein FR _min is a value of FR _n , a value less than FR _min indicates end of prefilter life. h) extrapolate the graph to deduce V _n at (FR _min ), the deduced value of V _n at FR _min is the estimated volume (VE) indicating prefilter life.

The server is also capable of storing data from the pressure sensing unit, when present; and incidents Έ’ when the pressure sensing unit detects pressure less than a predetermined value of pressure P _min .

It is preferable that when the pressure sensing unit is positioned downstream of the prefilter, the server is further capable of being configured to report that prefilter life is over if the Έ’ is reported for at least‘t’ number of times within a predetermined value of volume dispensed through the water treatment unit.

The server may further be configured to send alerts to change the prefilter. Sending of alerts may be via the display device or any other medium. The server is preferably capable of being configured to send alerts in advance of the end of prefilter life, for example at 80% of the VE, or any such value may be picked which gives sufficient time to change the prefilter before its life is over.

Display device

The predicted life of the prefilter according to the system and method of the present invention may be displayed on a display device which is a part of water treatment device or control module or server or is an is an independent portable device.

The display device is preferably a user interface of the water treatment device.

It is most preferable that the display device has a screen, preferably an LED screen to display the prefilter life.

The display device is capable of displaying other information with respect to the water purifier such as connectivity, quality of water dispensed, status of other filters and such similar information, data which is useful for the user or consumer.

It is possible that there are more than one display devices, such as one on the water treatment device, other on the server and one on an independent device, anyone or combinations thereof.

The display of the prediction of prefilter life could be graphical, numerical, statistical, such as display of colours for showing life of filter, timeline, maps, ladders, scales, graphs, percentages, decimal, fraction, pyramid, pie, circle, chart, bar graph, and the likes.

The display device of the present invention may also be used to show alerts for changing prefilter.

A portable device, as the name suggests is a device which is portable and has a communication module capable of communicating with the apparatus via the communication module of the apparatus. The portable device preferably comprises a hardware and a software.

The portable device comprises a communication module capable of communicating with the communication module of the apparatus when present and with the control module and/or server.

The portable device could be a laptop computer, a tablet, a phone, a computer or a hand- held device. It is highly preferred that the portable device comprises a mobile phone.

It is highly preferred that the portable device communicates through a conventional means such as electric, electronic or wired or through wireless means with the water treatment device and/or communication module and/or server. It is highly preferable that the portable device communicates through wireless means with the water treatment device.

It is also possible that the portable device communicates with the apparatus or server through an intermediate device, cloud, system, software etc. or the likes.

When the portable device is a phone, the display or the user interface of the information of the water treatment system is preferably through an APP.

Method

The present invention provides a method of method of predicting prefilter life, the method comprising steps of: i. providing the system according to the first aspect;

ii. recording values of V _n ;

iii. recording values of flowrate (FR _n ) sensed by the flow sensor, wherein FR _n is a direct function of the prefilter performance;

iv. plotting a graph of FR _n values against V _n values;

v. storing a predetermined value of flow rate FR _min ; wherein FR _min is the minimum value of FR _n , a value less than FR _min indicates end of prefilter life; and vi. extrapolating the graph to deduce V _n at (FR _m in), the deduced value of V _n at FR _min is the estimated volume (VE) indicating prefilter life.

It is preferred that the method further comprises reporting end of prefilter life through the display device.

It is most preferable to begin plotting of graph with at least 3 data points for a more authentic plotting of the graph.

The Data points of FR _n are collected at fixed intervals of V _n , for example after every V litres of volume of water is dispensed from the water treatment device, preferably between 1 to 50 litres.

It is preferred that according to the method of the present invention, when the pressure sensing unit is positioned downstream of the prefilter, the method further comprises reporting end of prefilter life when Έ’ is reported for at least‘t’ number of times for a predetermined value of volume dispensed through the water treatment unit and it is preferred that reporting end of life of the prefilter at an event Έ’ overrides the VE value at any stage of V _n during prefilter life.

This method takes care of the event when the prefilter could get such severely clogged that there is hardly any pressure of water sensed which has passed through the prefilter, indicating the end of life of prefilter.

The value of ‘t’ number of times is chosen at a higher value than at which normal or average expected low-pressure errors would be expected within a value of volume. For example, if on an average, an incident Έ’ is expected to occur once in 20 litres of dispensed through the water treatment unit, then if Έ’ occurs 10 times in 1 litre, it is an indication of end of prefilter life and therefore this value, overrides the VE value at any stage of V _n during prefilter life.

The method may further comprise of sending alerts to change the prefilter. Sending of alerts may be via the display device or any other medium. The alerts may be triggered in advance of the end of prefilter life, for example at 80% of the VE, or any such value may be picked which gives sufficient time to change the prefilter before its life is over.

Use

The present invention provides a system comprising:

A. a water treatment device comprising,

i. an inlet;

ii. a prefilter downstream of the inlet;

iii. a water treatment unit further downstream of the prefilter;

iv. a flow sensor positioned downstream of the water treatment unit;

v. an outlet for dispensing treated water; and

B. a control module, capable of,

i. storing data generated by the flow sensor;

ii. storing a value of volume dispensed (V _n ) from the water treatment device at a given time since the last incident of change or installation of prefilter; iii. storing incidents of change of prefilter; wherein, the control module is configured to: a) record values of flowrate (FR _n ) sensed by the flow sensor, wherein FR _n is a direct function of the water treatment system performance; b) plot a graph of FR _n values against V _n values;

c) store a predetermined value of flow rate FR _min ; wherein FR _min is a value of FR _n , a value less than FR _min indicates end of prefilter life. d) extrapolate the graph to deduce V _n at (FR _min ), the deduced value of V _n at FR _min is the estimated volume (VE) indicating prefilter life. for use in predicting prefilter life of the water treatment device.

The present invention provides a system comprising: A. a water treatment device comprising,

i. an inlet;

ii. a prefilter downstream of the inlet;

iii. a water treatment unit further downstream of the prefilter;

iv. a flow sensor positioned downstream of the water treatment unit;

v. an outlet for dispensing treated water; and

B. a control module, capable of,

i. storing data generated by the flow sensor;

ii. storing a value of volume dispensed (V _n ) from the water treatment device at a given time since the last incident of change or installation of prefilter; iii. storing incidents of change of prefilter; wherein, the control module is configured to: a) record values of flowrate (FR _n ) sensed by the flow sensor, wherein FR _n is a direct function of the water treatment system performance; b) plot a graph of FR _n values against V _n values;

c) store a predetermined value of flow rate FR _min ; wherein FR _min is a value of FR _n , a value less than FR _min indicates end of prefilter life. d) extrapolate the graph to deduce V _n at (FR _min ), the deduced value of V _n at FR _min is the estimated volume (VE) indicating prefilter life. for use in reporting prefilter life of the water treatment device, and preferably through a display device.

Use of the system of the present invention to send alerts for changing prefilter.

In an exemplary embodiment of the present invention, the control module stores data generated by the flow sensor; value of volume dispensed (V _n ) from the water treatment device at a given time since the last incident of change or installation of prefilter and incidents of change of prefilter. The control module also records values of flowrate (FR _n ) sensed by the flow sensor. Suppose the flow rate was sensed to be 400ml/min at the time of installation of the device or the change of prefilter, then this value is plotted against Volume O’, then the values taken at predetermined volume intervals are plotted, for example after every 50 litres.

A predetermined value of flow rate FR _min is stored in the control module for example 80ml/min, the graph is extrapolated to check the value of volume dispensed (V _n ) at 80ml/min, which shall then be the predicted life of prefilter. If suppose such value of V _n at which the FR _n values are extrapolated to meet 80ml/min is 2000 Litres, then that means that the VE, that is the estimated volume (VE) indicating prefilter life is 2000 litres, that is the prefilter needs to be replaced after 2000 litres of water is dispensed from the water treatment device. This will also be the case when the pressure sensing unit is positioned upstream of the prefilter. However, when the pressure sensing unit is positioned downstream of the prefilter, the control module also stores incidents Έ’ when the pressure sensing unit detects pressure less than a predetermined value of pressure P _min and is further configured to report that prefilter life is over if the Έ’ is reported for at least‘t’ number of times within a predetermined value of volume dispensed through the water treatment unit. So, if P _min is 5 psi and‘t’ is stored as 10 times and predetermined value of volume is 1 litre, then if the pressure sensing unit senses pressure less than 5 psi for at least 10 times, i.e., 10 times or more within a predetermined value of volume, i.e., 1 litre then the control module is configured to report end of life of the prefilter. This reporting of end of life happens irrespective of whatever is the estimated volume (VE) indicating prefilter life.

The various features of the present invention referred to in individual sections above apply, as appropriate, to other sections mutatis mutandis. Consequently, features specified in one section may be combined with features specified in other sections as appropriate. Any section headings are added for convenience only and are not intended to limit the disclosure in any way.