METHOD AND APPARATUS FOR FILTERING OF A LIQUID

Abstract: The invention relates to a method and apparatus for filtering a liquid. The filtering is conducted using one or several filtering elements (6) in the filtering room (5), the operation being based on the alternation of filtering stages and following air flushing stages. According to the invention, upon transferring from the flushing stage to the filtering stage, the filtering room (5) is filled with liquid so that the liquid pushes the flushing air in the room from the upper end (9) of the room into a separate air container (7) so that air is simultaneously compressed to a higher pressure in the container. During the filtering stage, air remains in the container (7), and after the filtering stage, air compressed into the container is allowed to push liquid out of the filtering room (5) with its pressure. Further, the connection between the air container (7) and the filtering room (5) can be arranged so that air compressed into the container participates in the backflushing of the filtering elements (6). The invention is especially applicable to an automatic filter filtering fuel or lubricant in a diesel motor.

Description: METHOD AND APPARATUS FOR FILTERING OF A LIQUID The present invention relates to a method for filtering a liquid, using at least one filtering element present in the filtering room, in which method the room is drained of the liquid after each filtering period, and the element is cleaned with flushing air directed through the room. Further, the invention relates to a filtering apparatus intended for applying the method. Continuous automatic filters with alternating filtering and flushing periods, are used, for example, in diesel motors for filtering fuel or lubricant. The filtering is used for removing the principally solid impurities wearing the motor. The patent publication US 4 256 583 discloses a filtering apparatus, in which the filtering is conducted alternately in two parallel filtering chambers, controlled by a rotating valve. The filtering chambers are cleaned with bac_<_flushing between the filtering periods. The patent application FI 982113, which is related to the present application according to the moment 2, section 2 of the Patent Act, discloses a filtering apparatus with three filtering units controlled with a common valve organ, two of the filtering units being intended to operate alternately in the actual filtering process, and the third one forming a reserve unit, into which the flow to be filtered is directed, as the two units mentioned first are being serviced. The valve organ may comprise a spindle with circular cross-section, the operation of which is based on axial movement and on rotary movement around the axle. When after the filtering stage, the flushing stage is adopted in the filtering room, the room is full of liquid, which the pressurised air used for the flushing pushes ahead into a separate reject channel. Besides emptying the filtering room, the flushing air flow cleans the filtering elements in the room with bacl lushing. After the flushing stage, the filtering room is again filled with liquid, according to the said patent application FI 982113 with liquid to be filtered, which is led from the inlet assembly for the filtered flow, for initiating the filtering period. The flushing air in the filter- ing room is then discharged into the air vent beginning from the upper end of the room. Air should be removed from the filtering room as completely as possible, because, for example, in a diesel motor, air bubbles must not be allowed to mix with the filtered fuel or lubricating oil. Some solutions are known, in which a float has been arranged to the upper end of the filtering room to close the exit route for air, as the room has been filled with liquid. After this, it is possible to open the outlet assembly for the filtered flow so that filtering may be conducted as a flow-through from the inlet assembly through the casing of the filtering element into the outlet assembly. The object of the invention is to provide a solution with which the construction formed by the filtering room and related channels can be simplified, the emptying of the filtering room from liquid may be intensified at the beginning of the flushing stage, and the danger that air and the liquid to be filtered be mixed during the filtering stage may be completely eliminated. It is characteristic of the method of the in- vention that, after the flushing stage, the filtering room is filled with liquid so that the liquid pushes the flushing air from the upper end of the room into a separate air container so that air is compressed to a higher pressure and that, after the end of the next filtering stage, liquid is pushed out of the filtering room with the pressure of air compressed into the air container. Thus, it is achieved with the invention that the air remaining in the filtering room after the flushing stage does not need to be removed from the filtering process, and no corresponding outlet channels are needed for it but, on the contrary, this air may be stored to be utilised at a later stage of the process. As the air container is separated from the filtering room, the liquid led into the room may also be allowed to fill part of the air container so that no air is left in the filtering room, and also air in the air container is effectively isolated from the filtering room. Thus, there is no danger that air and liquid be mixed in the filtering room during the filtering stage. After the filtering stage, air compressed into the air container effectively drains the filtering room from liquid so that it is then possible to lead the actual flushing air flow into the substantially empty filtering room. Emptying the filtering room substantially from liquid at the end of the filtering stage merely by opening the reject channel is also of advantage taking into consideration service measures performed in the filtering room. In the filtering room, the liquid to be filtered may be, for example, fuel oil at the temperature of 100 - 150°C which, for reasons of safety, is removed from the room before opening the cover of the room. In known solutions, bacl__flushing should be performed in the filtering room before the cover of the room can be opened. According to an especially advantageous embodiment of the invention, the discharge of compressed air from the air container into the filtering room occurs so that air participates in the backflushing of the filtering element or elements. The flushing effect of air is most intensely directed to the upper end of the filtering element, which first becomes free of the discharging liquid. As the air pressure drops, the flushing effect to the lower parts of the filtering element is left weaker. If however, the actual flushing air flow led through the lower part of the filtering room is simultaneously initiated, efficient bacl lushing is achieved to both ends of the element at the same time. The filtering apparatus of the invention intended to be used for applying the above method comprises at least one filtering element placed in the filtering room, which is equipped with an inlet assembly for the liquid flow to be filtered, with an outlet assembly for the filtered flow, and with an air channel for cleaning the filtering element with air flushing between the filtering periods. According to the invention, it is essential in the apparatus that the upper end of the filtering room is connected to the air container through a connection channel, air in the room being arranged to be compressed in the air channel as the room is filled with liquid. There is advantageously a connection from the air container through the connecting channel to the exhaust side of each filtering element in the filtering room, i.e. to the side from which the filtered liquid flow is discharged to the outlet assembly so that the air discharging under pressure from the air container is available for the back- flushing of the element. From the point of view of the design and space utilisation of the apparatus it may be appropriate to arrange the air container partly or entirely lower than the upper end of the filtering element and to arrange the connecting channel to connect the upper end of the filtering room with the lower end of the air container. As cylindrical filtering elements, so-called candles, are typically used in the filtering room, the centre of the room is easily left with unused space, which may especially advantageously be utilised by changing it to the air container required by the invention. The candle- shaped filtering elements may then be placed as a ring around the air container, or it is possible to arrange only one single cylindrical filtering element of sandwiched or fluted filtering material to surround the air container in the filtering room. The invention is next explained in more detail with the help of examples, referring to the enclosed drawings, in which Figure 1 shows a filtering apparatus of the invention in vertical section; Figure 2 shows the filtering unit in the apparatus as horizontal section II - II of Fig. l; Figure 3 is a vertical section of the upper end of the filtering unit in accordance with a second embodiment of the invention; Figure 4 is a vertical section of the upper end of the filtering unit according to a third embodiment of the invention; and Figure 5 shows the filtering unit of Fig. 4 in horizontal section V - V. The filtering apparatus of Fig. 1, which may, for example, be used as an automatic filter for the fuel or lubricant system in a diesel motor, comprises in accordance with the figure a base 1 and two parallel filtering units 2, on the alternating use of which the operation of the apparatus is principally based. The filtering units 2 are controlled with a spindle 3 so that, as the filtering is running in the one unit, the other unit is being cleaned by bacldlushing with compressed air, whereafter the functions are switched between the units. The apparatus also includes a third filtering unit, which is found behind the spindle 3 in the figure. The third filtering unit is controlled with the same spindle, and it operates as a reserve unit during the main- tenance of the units 2 shown in the figure. Of these parts, the structure and operation of the apparatus corresponds to the patent application FI 982113 or the international application PCT/FI99/00798, these applications being with this reference incorporated as part of this specification. In Fig. 1, the leftmost of the two filtering units 2 is in the filtering stage, in which the travel of the flow to be filtered through the unit is indicated with arrows. The spindle 3 guides the flow to be filtered to the units 2 from a common inlet channel (not shown) through the inlet assembly 4 into the filtering room 5 which, according to Fig. 2, includes eight cylindrical, candle-shaped filtering elements 6 arranged as a ring around the air container 7 separated from the centre of the filtering room. An axial connecting channel 8 connects the upper end 9 of the filtering room 5 and the lower end of the air container 7. During filtering, the filtering room 5 is completely filled with the liquid to be filtered. The liquid also fills the said connecting channel 8 and the lower part of the air container 7. Above the liquid level 11 in the air container, air is compressed to the pressure prevailing in the apparatus during filtration. typically to approx. 4 - 7 bar. The liquid to be filtered is infiltrated in the filtering room 5 through jackets manufactured of the filtering material of the filtering elements 6, such as metal or plastic net into the elements, and is discharged as cleaned through the open lower ends of the elements into the outlet assembly 12 of the spindle 3, from which the flow is directed into the outlet channel (not shown) common to the filtering units 2. In the leftmost filtering element 2 in Fig. 1, the inlet channel 13 for flushing air is closed by the valve 14 during the filtering stage. The rightmost filtering unit 2 in the figure is shown in the flushing stage, in which the valve 14 is open and the compressed air directed from the base 1 through the air channel 13 backflushes the fil- tering elements 6, whereafter it is discharged into the reject channel (not shown) guided by a reject spindle common to the units 2. At this stage, the filtering room as well as the air container 7 in the middle of it are empty from liquid. When transferring from the flushing stage to the filtering stage in the filtering unit 2, the filtering room 5 is first filled with liquid led slowly from separate filling channels 15. At this stage, both the inlet channel 13 for flushing air and the connection to the said reject channel are closed. The liquid, with which the filtering room 5 is filled, comprises filtered clean liquid led from the outlet assembly 12 for the flow. Upon initiating the filling, the filtering rooms 5 and the air channel 7 connected to it through the connecting channel 8 are full of air. During filling, the liquid pushes air ahead towards the air container 7, so that the air pressure increases. As the filling continues, the filtering room 5 is entirely filled with liquid, and liquid is additionally pushed into the air container 7 through the connecting channel 8 so that liquid fills the lower part of the container. Thus, air present in the filtering unit at the beginning of the filling is compressed into the air container 7, in which it is isolated from the filtering room 5 and in which it stays during the next filtering stage. The filtering stage is initiated by rotating the spindle 3 so that its inlet and outlet assemblies 4, 12 are connected to the respective assemblies of the filtering unit 2, and the flow to be filtered is allowed to travel through the filtering room 5 and the filtering elements 6 in it. The filtering stage in the filtering unit 2 ends as the spindle 3 rotates so that the flow assemblies 4, 12 into the inlet and outlet channels for the flow are closed. For flushing, the connection from the filtering room 5 into the reject channel is opened so that air compressed in the air container 7 is able to utilise its pressure to push the liquid out of the filtering room. In Fig. 1, the connecting channel 8 connects the air container 7 in the filtering room 5 outside the filtering elements 6 so that air compressed in the air container 7 empties the filtering room 5. The bacMushing of the filtering elements 6 is conducted with pressurised air led from the flushing air channel 13. The embodiment of the invention in Fig. 3 differs from the one shown in Fig. 1 ιr_ that that the connecting channel 8 leading to the air container 7 is connected inside the filtering elements 6 in the room through the upper end of the filtering room 5. For this purpose, the upper end of each candle-shaped filtering element 6 is provided with a flow opening 16. With this arrangement it is achieved that, as the flushing begins, air discharging under pressure from the air container 7 participates in the backflushing of the filtering elements 6 as the flushing effect is principally di- rected to the upper end of the elements. If flushing air flow is simultaneously initiated through the air channel 13, the effect of the flow being most efficiently directed to the lower ends of the filtering elements 6, these flows achieve a joint effect, in which the elements are efficiently flushed along their entire length. Figures 4 and 5 show an embodiment of the invention, in which air compressed into the container 7 in accordance with Fig. 3 may be used for backflushing the filtering element. Differing from the embodiments in Fig. 1 and 3, in this embodiment the filtering room 5 comprises one single cylindrical, fluted filtering element 17 surrounding the cylindrical air container 7 separated from the centre of the filtering room. The connecting channel 8 is connected to the interior of the filtering element 17 at the upper end 9 of the filtering room so that air discharging from the air container 7 has to penetrate the jacket of the filtering element as it travels into the reject channel foiming the exit route for liquid and flushing air. It is obvious for one skilled in the art that the various embodiments of the invention are not limited to the examples shown above, but they may vary within the scope of the following claims.

Claims: Claims 1. Method for filtering liquid with at least one filtering element (6, 17) in the filtering room (5), in which method the room is drained from liquid after every filtering stage, and the element is cleaned with flushing air led through the room, char- acterised in that, after the flushing stage, the filtering room (5) is filled with liquid so that liquid pushes the flushing air from the upper end (9) of the room into the separate air container (7), and air is compressed to a higher pressure, and that, after the next filtering stage, the liquid is pushed out of the filtering room utilising the pressure of air compressed into the air container. 2. Method according to claim 1, characterised in that, upon initiating the filling of the filtering room (5) with liquid, the outlet channel for flushing air is closed so that air filling the filtering room is entirely compressed by the liquid. 3. Method according to claim 1 or 2, characterised in that the compressed air is discharged from the air container (7) into the filtering room (5) so that it participates in the bac___flushing of one or several filtering elements (6, 17). 4. Method according to one of the preceding claims, characterised in that the flushing air is compressed to the operating pressure of the filtering apparatus prevailing in the air container (7). 5. Method according to one of the preceding claims, characterised in that the liquid pushes air from the upper end (9) of the filtering room (5) through the connecting channel (8) into the air container (7), which is at least partly placed lower than the upper end of the filtering room. 6. Method according to claim 5, characterised in that the liquid fills the lower end of the air container (7) through the connecting channel (8) so that the liquid level (11) in the air container is left below the upper end (9) of the filtering room (5). 7. Method according to one of the preceding claims, characterised in that the liquid to be filtered is fuel oil for a diesel motor. 8. Filtering apparatus for applying the method according to one of the preceding claims, the apparatus comprising at least one filtering element (6, 17) placed into the filtering room (5) and equipped with the inlet assembly (4) for the liquid flow to be filtered, the outlet assembly (12) for the filtered liquid flow, and the air channel (13) for cleaning the filtering element with air flushing between the filtering stages, characterised in that the upper end (9) of the filtering element (5) is through the connecting channel (8) connected to the air container (7), into which air in the room is arranged to be compressed as the room is being filled with liquid. 9. Filtering apparatus according to claim 8, characterised in that there is a connection (8, 9, 16) from the air container (7) to the exit side of each filtering element (6, 17) in the filtering room (5) so that air compressed into the air container is available for backflushing the element. 10. Filtering apparatus according to claim 8 or 9, characterised in that the air container (7) is at least partly arranged lower than the upper end (9) of the filtering room (5), and that the connecting channel (8) connects the upper end of the filtering room to the lower part (10) of the air container. 11. Filtering apparatus according to one of the claims 8 - 10, characterised in that the air container (7) is separated from the centre of the filtering room (5), and that the apparatus comprises cylindrical filtering elements (6) arranged as a ring around the air container. 12. Filtering apparatus according to one of the claims 8 - 10, characterised in that the air container (7) is separated from the centre of the filtering room (5), and that the apparatus comprises a cylindrical filtering element (17), which surrounds the air container in the filtering room. 13. Filtering apparatus according to claim 11 or 12, characterised in that the connecting channel (8) is situated in the air container (7) on its vertical axis, ending close to the lower end (10) of the air container.

Inventors: KOIVULA TUOMO, KOIVULA, TUOMO
Applicants: KOIVULA TUOMO, PARKER HANNIFIN OY, KOIVULA, TUOMO
Application year: 2000
Main classification: B01D29
IPC codes: B01D29, B01D35