Abstract: A method and apparatus for removing fine particulate matter from a fluid stream without interrupting the overall process or flow. The flowing fluid inflates and expands the flexible filter, and particulate is deposited on the filter media while clean fluid is permitted to pass through the filter. This filter is cleaned when the fluid flow is stopped, the filter collapses, and a force is applied to distort the flexible filter media to dislodge the built-up filter cake. The dislodged filter cake falls to a location that allows undisrupted flow of the fluid after flow is restored. The shed particulate is removed to a bin for periodic collection. A plurality of filter cells can operate independently or in concert, in parallel, or in series to permit cleaning the filters without shutting off the overall fluid flow. The self-cleaning filter is low cost, has low power consumption, and exhibits low differential pressures.

Abstract: A fuel tank deaeration and aeration system, including a first main filter device having an inlet and an outlet, wherein the inlet is in fluid communication with a fuel tank; and a second additional filter device having an inlet and an outlet, wherein the inlet is in fluid communication with the outlet of the main filter device, and the additional filter device outlet is in fluid communication with an environment of a vehicle, and wherein a bypass valve controls a bypass, which bypasses the additional filter device.

Abstract: Tangential flow filtration device is provided wherein liners are provided between the filtration element and the top and bottom holders or manifolds. The liners incorporate the flow channels and inlet and outlet ports, as well as a sensor mount. The liners are made of an inexpensive material and therefore are disposable after a single use, making it more cost effective to dispose of them than to clean the conventional manifolds. The sensor mount accommodates a removable sensor, and isolates it from the fluid path.

Abstract: A V-pack filter includes a frame construction having a first frame structure and a second frame structure. The V-pack filter also includes first and second panel sections mounted in extension between the first and second frame structures. The first panel section has first and second ends. The second panel section has third and fourth ends. The first and third ends have a first distance therebetween while the second and fourth ends have a second distance therebetween. The second distance is generally greater than the first distance. The first and second panel sections and the second frame structure define an air flow aperture. A seal arrangement circumscribes the air flow aperture and projects outwardly from the second frame structure. The first frame structure defines a first receiver indent. Assemblies and methods are also included.

Abstract: An apparatus, system, and method for preventing server contamination. The system includes a server rack and a contamination filter secured to the server rack. The contamination filter may be configured to filter particulate substances and/or chemical substances from air. The system may include a reaction coupon configured to indicate the presence of particulate substances and/or chemical substances in the air.

Abstract: A liquid degassing apparatus is arranged to limit pervaporation through a membrane by attenuating pressure oscillations developed by a vacuum pump. The attenuation is obtained through a combination of one or more flow restrictors and added volume chambers fluidly interposed between the degassing chamber and the vacuum pump. The pressure oscillation attenuation may further inhibit cross-contamination of pervaporated solvents among a plurality of distinct degassing chambers.

Abstract: A clog indicating device indicating clogging of a dust collecting filter in a dust collector id disclosed. The dust collector includes on an upper region of its casing an exhaust port opening upward, and a cover member is mounted interspatially above the exhaust port. A colored indicating float is so located as to be movable upward between the exhaust port and the cover member due to pressure of an air exhausted from the exhaust port. Clogging of a dust collecting filter is indicated according to a degree of exposure or a position in an up and down direction of the indicating float between the exhaust port and the cover member.

Abstract: A method for renewing a sheet-type filtering material to a flowing gas stream inside a conduit by converting some of the energy of a flowing gas stream traversing the filter assembly to rotate a propeller and the propeller shaft. The rotational energy from the propeller shaft is operably coupled to a gear that causes a supply of unused sheet-type filter material on a first side of the filter assembly top move across the filter assembly to a second side of the filter assembly, so that the portion of the sheet-type filtering material in a position to filter a flowing gas stream changes over time as the flowing gas stream rotates the propeller.

Abstract: The invention relates to a fan-and-filter unit to be mounted in the wall off a switch cabinet or housing, comprising a fan unit inserted in a fan housing, a filter mat arrangement mounted upstream of the fan unit and a fan cover immobilizing the filter mat. An embodiment advantageous for operation of the fan-and-filter unit consists in that the fan-and-filter unit has a filter mat monitoring unit which is designed to detect the service life and/or a degree of soiling of the filter mat arrangement and which comprises an insert integrated into the fan housing or the fan cover and having an illuminated display visible from the exterior of the fan cover facing away from the fan unit and being designed to display at least exceeding of a predetermined or predeterminable service life and/or a predetermined or predeterminable degree of soiling.

Abstract: A device for diagnosing a particle filter attached onto a main exhaust line of an internal combustion engine, wherein the diagnosis device includes, downstream from the first particle filter, a detection filter and a sensor for measuring an output parameter of the detection filter. The detection filter is arranged in a secondary exhaust line through which a first portion of the gases from the particle filter passes, wherein a second portion of the gases from the particle filter follows the main exhaust line. The device can be used for diagnosing particle filters for an automobile having a combustion engine.

Abstract: A control device for a filtration unit for filtering a fluid, the control device comprising an integrity test unit for performing an integrity test for checking the functional integrity of the filtration unit, and a reaction unit for determining a reaction based on a result of the integrity test.

Abstract: The present invention relates to a separating cyclone for separating a mixture of liquids into a heavy fraction, the cyclone comprising:—a cyclone tube (2) in which a flow space is defined, wherein the cyclone tube is provided with an inlet for infeed of a mixture of at least two different liquids, a heavy fraction outlet for discharging the heavy fraction separated from the mixture and a light fraction outlet for discharging the light fraction separated from the mixture;—a rotation generating unit (8) for setting into rotation the mixture fed in via the inlet;—a flow body (6) arranged substantially concentrically in the cyclone tube, in which body is provided a light fraction discharge channel (12) connected to the light fraction discharge, wherein the discharge channel has in flow direction a cross-section substantially decreasing along at least a portion of the length thereof.

Abstract: There is described a filtering device (1) for systems for supplying gas to internal combustion engines, comprising, integrated in the device, sensor means (10, 11, 12) for detecting the pressure and temperature of the gas being injected into the engine as well as the pressure at the inlet manifold of the engine.

Abstract: Methods and systems for monitoring the condition of a new air filter installed in an HVAC system are disclosed. In one example, an input that indicates a new air filter has been installed may be accepted, and in response, the HVAC system may be automatically operated in an air filter verifying mode, in which the fan of the HVAC system is activated to drive air through the new air filter. While in the air filter verifying mode, a measure related to an amount of flow restriction presented by the new air filter may be received. A status of the new air filter may be determined based, at least in part, on the received measure related to the amount of flow restriction presented by the air filter of the HVAC system. Once the status of the new air filter is determined, an indication may be displayed on a display, which may communicate the determined status of the new air filter to a user.

Abstract: A clean air filter may be used to set an air filter change threshold value for an air filter monitor installed in an HVAC system. The air filter change threshold value may be used to determine a status of an air filter (e.g., clean or dirty).

Abstract: A method and apparatus for supplying oxygen to meet a user demand in which oxygen is separated from air by an electrically driven oxygen separation device to supply oxygen to meet the user demand and to charge an adsorbent bed with all or part of the separated oxygen. When a user demand exists, oxygen can be supplied from both the electrically driven oxygen separation device and from oxygen desorbed from the adsorbent bed.

Abstract: A system for a vehicle includes a regeneration module and a disconnection indication module. The regeneration module indicates when a regeneration of a particulate filter is complete. The disconnection indication module receives a pressure difference across the particulate filter measured using delta pressure sensor. The delta pressure sensor generates the pressure difference based on first and second pressures upstream and downstream of the particulate filter applied to the delta pressure sensor using upstream and downstream pressure lines, respectively. In response to an indication that the regeneration of the particulate filter is complete, the disconnection indication module selectively indicates that the downstream pressure line is disconnected based on a comparison of the pressure difference and a predetermined pressure.

Abstract: A particulate matter detecting apparatus for an internal combustion engine that can estimate a discharge amount of the particulate matter accurately. The particulate matter detecting apparatus for an internal combustion engine, comprises: a sensor disposed at an exhaust passage of the internal combustion engine, the sensor including a pair of electrodes for detecting particulate matter in an exhaust gas; means for estimating a discharge amount of the particulate matter based on an output of the sensor, and means for acquiring a predetermined parameter that serves as an index for a rate with which the particulate matter in the exhaust gas is deposited on the sensor. The discharge amount estimating means corrects an estimated value of the discharge amount of the particulate matter based on the parameter acquired by the parameter acquiring means.

Abstract: A filter cassette and a method for allowing a leak to be detected are disclosed, in which the filter cassette comprises a main body defining a first chamber. The main body includes an inlet and an outlet, a filter separating the first chamber into first and second sub-chambers, the inlet being in fluid communication with the first sub-chamber and the second sub-chamber being in fluid communication with the outlet. The main body also includes a second chamber is defined by the main body and the filter, wherein in absence of a leak the second chamber is substantially not in fluid communication with the first chamber. The main body further includes a port in fluid communication with the second chamber, whereby measuring a fluid characteristic in the second chamber by means of the port allows a detection of a leak, i.e. an external leak or a bypass leakage.

Abstract: Systems and methods for processing high purity materials are disclosed. A unit operation processes a material stream, an operational parameter of the unit operation is monitored, and a standby unit is charged with pressurized gas to achieve system pressure. The material stream is diverted to the standby unit in response to the operational parameter of the unit operation registering a threshold value. Flow exiting the standby unit is first vented via an outlet, and then directed toward a point of use after the pressurized gas has been purged. The unit operation may then be serviced and subsequently brought back online. A second unit operation may process a second material stream simultaneously, and the second material stream may be periodically diverted to the standby unit in like manner, thus reducing line pressure variation. The disclosed method may be performed manually or implemented automatically through use of a controller.

Abstract: The present invention provides a system and method for transmitting information between a device within a housing to a second device, preferably a test or monitoring unit, outside of the housing. There are numerous issues associated with transferring information from within a sealed housing to an external device. In some cases, the use of wires inside the housing may be impractical, due to internal conditions, such as fluid flow, pressure or temperature. In one embodiment, the antenna of the external RF reading device is electrically connected to the dome of the housing. In another embodiment, the device within the housing is electrically connected to a housing component. In another embodiment, the gasket is used to pass information from within the housing to an external device.

Abstract: The present invention provides a system and method for transmitting information between a device within a housing to a second device, preferably a test or monitoring unit, outside of the housing. There are numerous issues associated with transferring information from within a sealed housing to an external device. In some cases, the use of wires inside the housing may be impractical, due to internal conditions, such as fluid flow, pressure or temperature. In one embodiment, the antenna of the external RF reading device is electrically connected to the dome of the housing. In another embodiment, the device within the housing is electrically connected to a housing component. In another embodiment, the gasket is used to pass information from within the housing to an external device.

Abstract: A real-time monitoring system that monitors various aspects of the operation of a refrigerant-cycle system is described. The system includes a processor that measures power provided to the refrigerant-cycle system and gathers data from one or more sensors in connection with a filter element.

Abstract: Methods for the purification of steam, systems for purifying steam, methods for measuring and/or controlling steam flow rates, and uses for purified steam are provide. Also provided are substantially gas-impermeable membranes, such as perfluorinated ionomers (e.g., perfluoroethylene-sulfonic-acid/tetrafluoroethylene membranes), having a high ratio of water vapor permeation relative to gas permeation through the membrane. Also provided are methods of operation of such membranes at relatively high operating temperatures for the purification of steam and for operation of such membranes at relatively low temperature and sub-atmospheric pressures for the purification of steam. In a preferred embodiment, the system 400 for purifying steam comprises heater 404 for creating a source of a steam feed, and a purification device 416 for housing a substantially gas-impermeable membrane 424. In the operation of system 400, water, such as deionized water, is added to vessel 402 to provide a source of the steam feed.

Abstract: A particulate matter sensor includes a first detection filter provided in an exhaust gas flow passage and capable of collecting particle matter. A second detection filter is provided on a downstream side of the first detection filter in the exhaust gas flow passage and capable of collecting the particle matter. A first differential pressure detection unit is configured to detect a first differential pressure between pressures of an upstream side and the downstream side of the first detection filter. A second differential pressure detection unit is configured to detect a second differential pressure between pressures of an upstream side and a downstream side of the second detection filter. A particle matter amount detection unit is configured to detect an amount of particle matter based on a detection result of the first differential pressure detection unit and a detection result of the second differential pressure detection unit.

Abstract: A system and method for supercritical fluid enrichment of radioactive isotope/s are disclosed. The method involves pressurizing an outer chamber and an inner centrifugal chamber of a stage to supercritical pressure; supplying material including target isotope/s at supercritical pressure to the inner chamber; spinning the inner chamber to centrifuge the material including target isotope/s; providing a differential pressure between the inner chamber and the outer chamber; wherein windows in the inner chamber enable passage of the target isotope from the inner chamber to the outer chamber in response to the differential pressure.

Abstract: An air treatment apparatus and method are disclosed in the present invention, wherein, at least one air treatment unit is included. The unit comprises air inlet, air outlet, air treatment devices and connecting components. The air treatment device is located between the air inlet and the air outlet. The air treatment device comprises at least one of the following components: component for air purification and filtering, blow-through fan, draw-through fan, pump, component for heating, component for dehumifying, component for humidifying, component for air-cooling. The air treatment unit can be used alone for improving the air quality of the environment. When more than one unit are connected together with the connecting components, the units are teamed up and work together, and an air treatment system is formed.

Abstract: The present invention describes a system and method for accurately measuring the pressure within a filter housing. A pressure sensor and a communications device are coupled so as to be able to measure and transmit the pressure within the filter housing while in use. This system can comprise a single component, integrating both the communication device and the pressure sensor. Alternatively, the system can comprise separate sensor and transmitter components, in communication with one another. In yet another embodiment, a storage element can be added to the system, thereby allowing the device to store a set of pressure values. The use of this device is beneficial to many applications. For example, the ability to read pressure values in situ allows integrity tests to be performed without additional equipment. In addition, integrity testing for individual filters within multi-filter configurations is possible.

Abstract: A filter, in particular for compressed gas systems, includes a filter top part having at least one inlet channel and at least one outlet channel and a filter bottom part having a filter element, wherein the filter top part has a pressure-resistant housing and an insert which is suited in an optimal manner to the course of the inlet and outlet channels.

Abstract: A filter system for an explosion-proof enclosure is described herein. The filter system can include a pre-filter assembly located outside the explosion-proof enclosure. The pre-filter assembly can include a pre-filter material configured to control air passing therethrough. The filter system can also include a filter assembly coupled to the pre-filter assembly. The filter assembly can further control the air received from the pre-filter assembly and passing therethrough into the explosion-proof enclosure.

Abstract: A system recognizes a check-up time of a filter of an air cleaner. The system includes a power unit that supplies power to the system, a pressure sensor that measure pressure of a filter, at an outlet connected with a filter unit, a conversion circuit that converts the measured value into a predetermined type, a processor that controls the measurement period of the pressure sensor and receives and compare the measured value converted by the conversion circuit with a predetermined reference value, and a display unit that displays a filter replacement period.

Abstract: A method is described for identifying faults relating to an HVAC system, such a clogged filter. Sensor data is used to estimate HVAC system efficiency. Trends in system efficiency are then used to identify faults such as clogged filters. The sensor(s) can include one or more of the following types: optical sensor, temperature sensor, pressure sensor, acoustic transducer, humidity sensor, resistive sensor, capacitive sensor, and infrared sensor. The efficiency estimation can also be based on conditions external to the building, such as data from exterior sensors and/or data gathered from third parties such as government or private weather stations. The efficiency estimation can also be based on performance metrics such as the time used to reach a set point temperature. The fault identification includes filtering out non-fault related events. An instrumented air filter for use with an HVAC system is also described.

Abstract: One example embodiment includes a system for removing cooling liquid from a mist. The system includes an intake, where the intake is configured to receive the cooling mist. The system also includes a mist filter, where the mist filter is configured to remove cooling liquid from the mist. The system further includes an exhaust, where the exhaust is configured to output the demisted air.

Abstract: Embodiments of the invention generally include a filter housing having a bagging ring coated to enhance a bag-to-bagging ring seal. In one embodiment, the housing assembly includes a housing having an inlet, an outlet and an access port. A bagging ring is disposed around the access port and includes a material having a property that enhances the bag-to-bagging ring seal. Examples of materials that have a property that enhance the bag-to-bagging ring seal include materials that are attracted to a plastic bag, materials that are tacky, materials that have a static attraction to a plastic bag.

Abstract: An active carbon filter unit for a tank system consists of a housing (13) in which two chambers (31, 32) are formed, carrying an active carbon filling, which form a section of a flow path which at its one end leads via a valve (6) and an air filter (7) into the ambient atmosphere and at its other end leads via a valve (9) and a non-return valve (10) to a connection for producing an underpressure or into the suction region of an internal combustion engine and via a connection (17) into the tank system. The valves (6, 9), the non-return valve (10) and a housing part (27) receiving the electrical connections thereof are part of a uniform control module (15), which is exchangeably inserted into a recess (14) of the housing (13).

Abstract: A gas liquid separator system for a hydrogen generating apparatus includes a collection area for collecting liquid from the generated gases. To empty the collection area occasionally so that liquid does not build up and become entrained again in the dried gas, a vent solenoid is provided in communication with the collection area and a pump is used to create a vacuum periodically on the electrolysis cells. Such arrangement is used to open the liquid gas filter and possibly just the sump to atmosphere occasionally and vacuum generated to draw the liquid from the sump back to the electrolysis cells.

Abstract: A method for determining the charge state of a particle filter installed in the exhaust gas line of an internal combustion engine comprises the following steps: determining the exhaust gas volumetric flow in the flow direction of the exhaust gas downstream of the particle filter (2), detecting the pressure present in the exhaust gas line (1) in the direction of flow of the exhaust gas prior to the particle filter (2), comparing the exhaust gas volumetric flow determined hinter the particle filter (2) with the detected pressure present upstream of the particle filter (2) and evaluating the results of the comparison with consideration to the exhaust gas back pressure of the uncharged particle filter (2) and the exhaust gas back pressure caused by the particle filter charge, said pressure being higher than the uncharged filter. Further described is a corresponding device for reducing the particle emissions of an internal combustion engine.

Abstract: A display device of a dryer, which can achieve the reliability of a function to display a clogging degree in the dryer, is disclosed. The display device includes a display unit for displaying a clogging degree of an air passage through at least one level indicator, and a controller for controlling the display unit when power is supplied, such that the level indicator flickers for a predetermined time, and then displays the clogging degree of the air passage. The display for the clogging degree of the air passage is executed, following the display of a normal operation state of the display unit.

Abstract: A system and process for gas homogenization is disclosed. This has application in the areas of generation of gas and its conversion to electricity in downstream applications. The homogenization system minimizes variance in the gas characteristics (composition, flow, pressure, temperature), thereby rendering a steady stream of gas of consistent quality to the downstream machinery. This homogenization system can be adjusted to optimize the output gas stream for specific end-applications, or to optimize the output gas stream for different input feedstocks. This ensures that overall conversion efficiencies are maximized while keeping the process cost-effective. Such a uniform, steady output gas stream has a wide range of applications in the broad areas of generation of electricity (e.g. using internal combustion engines and combustion turbine engines), chemical synthesis (e.g.

Abstract: An exhausting method includes determining an exhaust flow rate of a process gas to be a predetermined value that is less than or equal to a gas flow rate corresponding to a maximum process capability of a purification system when the process gas is diluted to a lower explosive limit; calculating a pressure drop amount per unit time to maintain the determined exhaust flow rate of the process gas, based on a relation between the exhaust flow rate and the pressure drop amount per unit time; and evacuating an inside of the chamber to maintain the determined exhaust flow rate, while controlling the pressure through an automatic pressure control valve by setting a target pressure value to be updated as a control value of the automatic pressure control valve at every predetermined time interval so as to achieve a calculated pressure drop amount per unit time.

Abstract: A heating, ventilating and air conditioning (HVAC) return air system actuator device which could, among other things, be employed to notify a user of a clogged air filter and/or disperse a fragrance into a forced air HVAC system is disclosed. In one embodiment the actuator device has a movable actuator mounted within a housing. The movable actuator moves in response to a user pre-set pressure differential. When the pre-set pressure differential is reached, the movable actuator impacts a lever which activates a switch. The switch could be connected to a host of items such as a light emitting device to notify the user to a clogged air filter condition and/or to activate a pump to release a fragrance into the HVAC system.

Abstract: An air filter with a clog-detecting device includes a housing having a wind outlet and a wind intake, a filter unit positioned between the wind outlet and the wind intake, an exhauster disposed between the wind outlet and the filter unit, a magnetic induction unit positioned on the exhauster, and a warning unit assembled on the housing and electrically connected with the magnetic induction unit. A metallic plate is axially fixed on the rotating spindle of a motor and positioned adjacent to the magnetic induction unit, having its upper side formed with at least one projection to enable the magnetic induction unit to induce the metallic plate and produce pulse signals. Thus, by detecting the frequency of the pulse signal, a user can know whether the air filter is clogged or not and proceed to remove the clogged condition to let the air filter continue to work normally.

Abstract: A drainage system is for a compressor assembly that includes at least one separator with a chamber. The system includes a drain valve fluidly coupled with the separator chamber and adjustable between open and closed states. An actuator is operatively coupled with and adjusts the valve between the open and closed states or/and a sensor senses when the valve is open. A pressure sensor is configured to sense pressure within the chamber and a logic circuit is coupled with the pressure sensor and determines when the valve either has been or should have been adjusted to the open state. The logic circuit also generates an output signal or/and operates a device when the chamber pressure remains substantially constant or varies by less than a predetermined amount subsequent to the valve being opened and/or when the chamber pressure varies by at least the predetermined amount after the valve is opened.

Abstract: An air filter coupled to an air inlet, which draws in air. The air filter is automatically cleaned to prevent clogging. When the supply of power is cut off during a cleaning operation sequence of the air filter and the electronic device restarts operation thereafter, the interrupted cleaning operation sequence is completed. An automatic cleaning operation may be performed on the air filter when a video projector, which serves as an electronic device, starts to operate. In addition, an automatic cleaning operation may he performed on the air filter when clogging of the air filter is detected.

Abstract: An inlet filter house is provided for use with a turbine engine including an inlet duct. The inlet filter house is coupled to the inlet duct and includes an inlet hood including a filter assembly selectively positionable between an operating position and a bypass position. An actuating assembly is coupled to the filter assembly to selectively position the filter assembly. A sensor is configured to detect at least one operating parameter. A controller is coupled to the sensor for actuating the actuating assembly based on the at least one operating parameter.

Abstract: A self-governing continuously variable inertial gas-liquid separator has an axially movable valve controlling axial flow through a nozzle orifice, and a variable flow controller upstream of and controlling the valve.

Abstract: A degassing device (203) comprises a first chamber (21) having an inlet for a liquid, and a second chamber (22) having an opening (23) closed by a hydrophobic membrane (24) and an outlet (25) for discharging the liquid. The first chamber (21) has a downstream portion that partially extends within the second chamber (22) and communicates therewith by a passageway (28). The second chamber (22) has a downstream portion that extends below the passageway (28) and asymmetrically surrounds the downstream portion of the first chamber (21).

Abstract: A real-time monitoring system that monitors various aspects of the operation of a refrigerant-cycle system is described. In one embodiment, the system includes a processor that measures power provided to the refrigerant-cycle system and that gathers data from one or more sensors and uses the sensor data to calculate a figure of merit related to the efficiency of the system. In one embodiment, the sensors include one or more of the following sensors: a suction line temperature sensor, a suction line pressure sensor, a suction line flow sensor, a hot gas line temperature sensor, a hot gas line pressure sensor, a hot gas line flow sensor, a liquid line temperature sensor, a liquid line pressure sensor, a liquid line flow sensor. In one embodiment, the sensors include one or more of an evaporator air temperature input sensor, an evaporator air temperature output sensor, an evaporator air flow sensor, an evaporator air humidity sensor, and a differential pressure sensor.

Abstract: An improved system and method for monitoring contamination loading of a filter in a biological safety cabinet comprising a housing defining a work chamber and a filtration chamber, a system for circulating air between the work chamber and the filtration chamber via a fan which draws air under negative pressure from the work chamber and delivers the air under positive pressure through the filter and into the filtration chamber. The filter monitoring system determines a pressure differential between the negative and positive air pressure at opposite sides of the fan, and evaluates the degree of contamination loading of the filter on the basis of the pressure differential. An air flow baffle is disposed within the filtration chamber adjacent the fan for dividing the pressurized air delivered by the fan and partially redirecting a portion thereof for more uniformly delivering the air to the filter.

Abstract: A furnace filter indicator system comprises a pressure differential switch that monitors air pressure near a furnace filter, and a transmitter coupled to the pressure differential switch sends a signal to a receiver within a thermostat. The receiver includes an indicator for indicating the status of the furnace filter. If the pressure differential near the furnace filter triggers the switch, then the indicator will receive a “dirty” signal and will indicate that the furnace filter is dirty and should be replaced. The furnace filter indicator system is able to be installed on a previously installed furnace/thermostat system by utilizing the pre-existing wiring.