2. BACKGROUND OF THE INVENTION The filtration of molten polymers is necessary while producing man-made fibers, film, etc. The production processes require continuous flow of clean molten polymer. Impurities, such as contaminants and gels, tend to cause fiber breakage or film ripping during the spinning and orientation phases.

Continuity and uniformity of flow are critical process conditions. Stagnation areas and creeping flows cause polymer degradation due to high residence time at elevated temperatures. Degradation products add impurities to the polymer stream being processed. These impurities have to be removed in order to avoid production problems mentioned earlier. Consequently, the residence time of a molten polymer in a filter system is a critical factor.

Currently, most of the filtration processes are carried out using the so-called screen changer for a small installed filtration area as shown in U. S. Patent No. 3,007,199 (Curtis), and systems that contain two filter housings and two diverter valves for a large installed filtration area as shown in U. S. Patent No. 3,833,121 (Singleton et al) and in U. S. Patent No. 3,727,767 (Itter et al) While there exist many types of screen changers and other small area filters, there is a limited availability of large-filter-area polymer filter, most of which are similar in construction. In these type of filters, the molten polymer flows through the inlet diverter valve, then through one of the filter housings and out through the second outtet diverter vatve. When the filter elements in the housing become exhausted, the flow gets diverted to the second housing, which has fresh filter elements. The exhausted filter housing is then removed, cleaned, returned with fresh filter elements, and put on stand-by mode until the second housing becomes exhausted.

The diverter valves regulate the flow at the inlet and at the outlet of the system. When switching from one filter housing to the second, the valve at the inlet is moved first, allowing a small portion of the flow to enter the fresh filter housing. The valve at the outlet side remains unchanged. A vent valve on the fresh filter housing is opened to allow the incoming product flow to fill the filter housing completely (venting or bleeding of the filter housing to come on-stream). When the fresh filter housing is completely filled with product, the vent valve is closed and the diverter valves at the inlet and at the outlet are moved simultaneously to force the complete product flow through the fresh filter housing, thus taking the first filter housing off-stream.

It may be noted, that because of the bleeding and venting phase, the feed portion used to fill the fresh filter housing sees, at an assumed bleed flow of ten percent of total flow, a residence time ten times that of the normal feed flow. As a consequence, the above described product degradation may occur.

Filter systems with two filter housings and two diverter valves have an installed filter area equal to twice the filter area that is on-stream. Normally at least three complete filter housings are needed for continuous operation: one housing on-line, one housing on stand-by and one housing undergoing external cleaning and replacing of filter elements.

The diverter valves define the most critical parts of these double filter systems. It is particularly difficult to design and manufacture such valves absolutely free of gaps, dead flow areas, and areas with reduced flow velocity. In the filtration of molten polymers, such gaps and areas with different flow characteristics may lead to product degradation with subsequent production problems as described earlier. In addition, it may be noted that in case of an error where an operator completely shifts either one of the inlet or outlet diverter valve without the other, when the product it flowing, the system will dead- head the pump/extruder and may cause the activation of the safety device such as a rupture disk.

Such systems are not inherently safe and do not normally have safety interlocks when provided with manual operation.

Also, filter systems with two filter housings and two diverter vafves do not offer the flexibility to easily change the filtration area of the installed filters in case of production rate and/or filter rating change requirements. This would require a variety of housing sizes to accommodate a variety of production rates and filter ratings.

OBJECTS OF THE INVENTION The primary object of the invention is to provide an apparatus and a process to continuously filter highly viscous fluids, in particular molten polymers and to overcome the disadvantages associated with the prior art.

Another object of the invention is to provide an apparatus and a process to narrow and minimize the residence time distribution of the flowing products.

Another object of the invention is to provide an apparatus and a process without the use of dedicated diverter valves.

Another object of the invention is to provide an apparatus and a process in which the entire available filtration area is used in the best way possible.

Another object of the invention is to provide an apparatus and a process in which the filter replacement would be achieved without flow interruption.

Another object of the invention is to provide an apparatus and a process in which only one bleeding and venting position is used.

Another object of the invention is to provide an apparatus and a process in which the filtration area may be changed without product flow interruption.

Another object of the invention is to provide an apparatus and a process in which the filtration area may be changed without changing the main apparatus assembly.

Another object of the invention is to provide an apparatus and a process with inherent safety of operation.

Another object of the invention is to provide an apparatus and a process in which the filter elements may be cleaned in place with the filtrate or another fluid reverse-flow.

SUMMARY OF THE INVENTION The basis for the invention is the idea to have a filter system for highly viscous liquids, in particular molten polymers, that provides continuity, that offers a desired range of filter area on-stream, that eliminates the need for switch-over valves, that avoids prolonged residence times typical of bringing fresh filter area on-stream, that needs only one bleeding and venting position, and that offers inherently safe operation.

A process and a filter system according to the invention with the features of the listed claims m neet the above requirements.

The invention defines a continuous filtration process. There is no interruption of operation foreseen whenever filter area gets exhausted. By rotating the filter assembly of the filter system, a small portion of the filter area is taken off-line, and then a fresh filter housing subassembly is introduced to the flow.

During rotation, all but one of the multiple filter housings on-stream remain on-stream.

The invention includes a filter system with basically multiple filter housing subassemblies that are assembled and affixed around rotating inlet and outlet headers which in turn are fitted to fixed inlet and outlet collectors, forming a rotatable filter assembly that at the same time allows a uniform product flow to continuously pass through all of the installed filter housings during the normal filtration cycle, and the majority of the installed filter housings during the rotation cycle. In the rotation cycle, when necessary, the rotatable filter assembly is rotated so that one housing subassembly is isolated from the flowing product and in turn gets depressurized through the depressurization port and then is removed or prepared for servicing and eplacement of the filter element (s). After the service completion, the rotatable filter assembly is rotated further to the one and only bleeding and venting position so that the newly serviced housing subassembly can be filled with product by bleeding through the unique inlet bleeding port and vented through the outlet vent before the rotatable filter assembly is rotated further in order to return it to the filtration service. The rotation cycle would then be repeated for the service of the remaining housing subassemblies. Provisions to decrease the installed filtration areas are made by removing one or more housing subassemblies and replacing them with plugs. Provisions to increase the installed filtration areas are made by removing one or more housing subassemblies and replacing them with larger ones.

The product flow enters the main ; inlet and then gets distributed, by the inlet distributor flow channel, over any desired number (In this case 8 ports are shown in the drawings, this can be changed to any desired number of ports with corresponding housings) of inlet ports. The flow then enters the filter inlet housing, which may have any desired type of opening, and then enters the filter element housings with one or more filter elements. The flow then enters the filter element (s) and then the outlet housing, which may have any desired type of opening, then enters the outlet port. The flow passing through the individual outlet ports is then collected in the outlet collector flow channel. The flow then exits the system through the main outlet.

The filter system according to the invention forces the product flow from its original flow path into the distributor serving multiple filter housings. The size and shape of the distributor, as well as the size and the number of filter housings can be scaled according to individual needs, putting no fundamental restrictions on the filter area that may be installed.

To change filter housing subassemblies or the filter element (s), the filtration process according to the invention lacks the need to install specific diverter valves. The flow distribution over the multiple housings is affected by the fixed inlet distributor and outlet collector, which need not to be changed during any phase of operation.

The particular advantage of the invention for the changing : ot axhatistsdwñlter. a. req. inethe<BR> <BR> <BR> circumstances that only a part of the filter area on line at any gien'tirrie is being replaced by fresh filter area. During normal operation, multiple filter housing subassemblies, say for example ten are on-stream. All these housings see, on the average ten percent of the incoming flow. Bleeding takes place for only one fresh filter housing subassembly at any given time. Assuming ten percent of the flow is used for bleeding, then the bleeding flow portion takes only so much time, as is the typical residence time for the product in the filter during normal operation. After bleeding, one filter housing subassembly is turned off-stream ; the just bled and vented housing subassembly is turned on-stream.

A provision to have one filter housing subassembly on stand-by mode is here considered. This allows the simultaneous removal and introduction of filter housing subassemblies without any change to the size of the installed area. This provision is realized by altering the design of the inlet distributor and outlet collector.

Compared to the known filter operation processes as referred to in the prior art, the invention offers the possibility to replace the exhausted filter area one fraction by fraction at a time.

Preferably a filter system according to the invention is provided in such a way that the system is self- cleaning by means of a reverse flow of clean filtrate or another suitable fluid through the exhausted filter area. The changing of exhausted filter elements can be avoided by such a reverse flow of clean filtrate or another suitable fluid.

The critical design area of the filter system according to the invention is the sealing of the rotating inlet and outlet headers to the inlet fixed distributor and outlet fixed collector respectively. Given the specific process conditions, an appropriate seal would be provided to meet such conditions. The seals may be made of a variety of elastomeric materials, or a special wear-resistant coating may be applied to a metal surface to affect a metal to metal seaiing.

BRIEF DESCRIPTION OF THE DRAWINGS The objects, features and advantages of the invention will become more apparent from the following brief description of the drawings: FIG 1. Front view of filter assembly according to invention.

FIG 2. Top view of inlet assembly. Here the outlet assembly is not shown.

FIG 3. Bottom view of outlet assembly. Here the inlet assembly is not shown.

FIG 4. Top view of inlet assembly where filter housing subassemblies are rotated so that a filter housing subassembly is isolated for service. Here the outlet assembly is not shown.

FIG 5. Top view of inlet assembly where filter housing subassemblies are rotated further so that a filter housing subassembly is in the feed bleed position. Here the outlet assembly is not shown.

FIG 6. Top view of inlet assembly where filter housing subassemblies are rotated further so that the newly serviced filter housing subassembly is returned the to filtration service. Here the outlet assembly is not shown.

FIG 7. Bottom view of outlet assembly where filter housing subassemblies are rotated so that a filter housing subassembly is isolated for service. Here the inlet assembly is not shown.

FIG 8. Bottom view of outlet assembly where filter housing subassemblies are rotated further so. that a filter housing subassembly is in the vent position. Here the inlet assembly is not shown.

FIG 9. Bottom view of outlet assembly where filter housing subassemblies are rotated further so that the newly serviced filter housing subassembly is returned the to filtration service. Here the inlet assembly is not shown.

FIG 10. Top view of inlet assembly where some of the filter housing subassemblies are removed to reduce the installed filtration area..

FIG 11. Bottom view of outlet assembly where some of the filter housing subassemblies are removed to reduce the installed filtration area.

FIG 12. Top view of inlet assembly where the filter housing subassemblies are replaced with larger ones to increase the installed filtration area.

FIG 13. Bottom view of outlet assembly where the filter housing subassemblies are replaced with larger ones to increase the installed filtration area.

FIG 14. Top view of inlet assembly where some of the filter housing subassemblies, with larger installed filtration area, are removed to reduce the installed filtration area.

FIG 15. Bottom view of outlet assembly where some of the filter housing subassemblies, with larger installed filtration area, are'removed to reduce the installed filtration area.

FIG 16. Top view of inlet assembly where one housing subassembly is normally on stand-by mode.

FIG 17. Bottom view of outlet assembly where one housing subassembly is normally on stand-by mode.

FIG 18. Top view of inlet assembly with the reverse flow outlet port. Here the outlet assembly is not shown.

FIG 19. Bottom view of outlet assembly for the clean. filtrats reverse flow case. Here the inlet assembly is not shown.

FIG 20. Top view of inlet assembly in the reverse flow mode. Here the outlet assembly is not shown.

FIG 21. Bottom view of outlet assembly in the reverse flow mode. Here the inlet assembly is not shown.

FIG 22. Bottom view of outlet assembly with the reverse flow inlet for another liquid reverse flow case. Here the inlet assembly is not shown.

FIG 23. Bottom view of outlet assembly for another liquid reverse flow mode. Here the inlet assembly is not shown.

FIG 24. Front view of the combined rotating inlet and outlet headers, and the combined inlet fixed distributor and outlet fixed collector.

SPECIFIC DESCRIPTION By its nature, the invention is subject to many design variations and details. The following figures are to be considered schematic illustrations of the concepts and should not be used as limiting design factors: FIG. 1 Schematically shows the filter system according to the invention with a main inlet (13) and a main outlet (14). Attached to the main inlet (13) is an inlet fixed distributor (1) with an inlet distribution flow channel (5). Attached to the main outlet (14) is an outlet fixed collector (2) with an outlet distributor flow channel (6). A rotating inlet header (3) with inlet ports (17) is installed around the inlet fixed distributor (1). A rotating outlet header (4) with outlet ports (18) is installed around the outlet fixed collector (2). Filter housing subassemblies ; comprising of an inlet housing (7) with a housing inlet channel (9), a filter element housing (12) in which the filter element (s) (11) are located, and an outlet housing (8) with a housing outlet channel (10), are affixed to the rotating inlet header (3) and the rotating outlet header (4). The filter housing subassemblies along with rotating inlet header (3) and the rotating outlet header (4) form one whole rotatable filter assembly.

FIG. 2 Schematically shows the top view of the main inlet (13), the inlet fixed distributor (1) with the- inlet distributor flow channel (5) and the inlet bleed (15). A rotating inlet header (3) with inlet ports (17) and oval port (21) is installed around the inlet fixed distributor (1). The inlet housing (7) and the filter element housing (12) in which the filter element (s) (11) are located are affixed to the rotating inlet header (3).

FIG. 3 Schematically shows the bottom view of the main outlet (14), the outlet fixed collector (2) with the outlet distributor flow channel (6) and the outlet vent (16) and depressurization port (20). A rotating outlet header (4) with outlet ports (18) is installed around the outlet fixed collector (2). The outlet housing (8) and the filter element housing (12) in which the filter element (s) (11) are located are affixed to the rotating outlet header (4).

FIG. 4 Schematically shows the top view of the main inlet (13), the inlet fixed distributor (1) with the inlet distributor flow channel (5) and the inlet bleed (15). A rotating inlet header (3) with inlet ports (17) and oval port (21) is installed around the inlet fixed distributor (1). In this view, the rotating inlet header (3) is rotated so that one housing subassembly (7,11,12) is depressurized and isolated for service.

The inlet housing (7) and the filter element housing (12) in which the filter element (s) (11) are located are affixed to the rotating inlet header (3).

FIG. 5 Schematically shows the top view of the main inlet (13), the inlet fixed distributor (1) with the inlet distributor flow channel (5) and the inlet bleed (15). A rotating inlet header (3) with inlet ports (17) is installed around the inlet fixed distributor (1). In this view, the rotating inlet header (3) is rotated further so that the same housing subassembly (7,11,12) that was isolated as shown in FIG. 4 is in the bleed position. The inlet housing (7) and the filter element housing (12) in which the filter elements) (11) are located are affixed to the rotating inlet header (3).

FIG. 6 Schematically shows the top view of the main inlet (13), the inlet fixed distributor (1) with the inlet distributor flow channel (5) and the inlet bleed (15). A rotating inlet header (3) with inlet ports (17) is installed around the inlet fixed distributor (1). In this view, the rotating inlet header (3) is rotated further so that the same housing subassembly (7,11,12) that was bled as shown in FIG. 5 is returned to the filtration service. The inlet housing (7) and the filter element housing (12) in which the filter element (s) (11) are located are affixed to the rotating inlet header (3).

FIG. 7 Schematically shows the bottom view of the main outlet (14), the outlet fixed collector (2) with the outlet distributor flow channel (6) and the outlet vent (16) and depressurization port (20). A rotating outlet header (4) with outlet ports (18) is installed around the outlet fixed collector (2). In this view, the rotating inlet header (3) is rotated so that one housing subassembly (8,11,12) is depressurized and isolated for service. The outlet housing (8) and the filter element housing (12) in which the filter element (s) (11) are located are affixed to the rotating outlet header (4).

FIG. 8 Schematically shows the bottom view of the main outlet (14), tAe otillet-flpd ct) lli ! ctar. (2)"t4<BR> <BR> <BR> <BR> the outlet distributor flow channel (6) and the outlet vent (16) and depressurization port (20). A rotating outlet header (4) with outlet ports (18) is installed around the outlet fixed collector (2). In this view, the rotating outlet header (4) is rotated further so that the same housing subassembly (8,11,12) that was isolated as shown in FIG. 4 and 7 is in the vent position. The outlet housing (8) and the filter element housing (12) in which the filter element (s) (11) are located are affixed to the rotating outlet header (4).

FIG. 9 Schematically shows the bottom view of the main outlet (14), the outlet fixed collector (2) with the outlet distributor flow channel (6) and the outlet vent (16) and depressurization port (20). A rotating outlet header (4) with outlet ports (18) is installed around the outlet fixed collector (2). In this view, the rotating-outlet header (4) is rotated further so that the same housing subassembly (8,11,12) that was isolated as shown in FIG. 5 and 8 is in the bleed position. The outlet housing (8) and the filter element housing (12) in which the filter element (s) (11) are located are affixed to the rotating outlet header (4).

FIG. 10 Schematically shows the top view of the main inlet (13), the inlet fixed distributor (1) with the inlet distributor flow channel (5) and the inlet bleed (15). A rotating inlet header (3) with inlet ports (17) and oval port (21) is installed around the inlet fixed distributor (1). The inlet housing (7) and the filter element housing (12) in which the filter element (s) (11) are located are affixed to the rotating inlet header (3). Plugs (19) serve to block the flow to the inlet ports (17) so that some of the housing subassemblies (7,11,12) can be removed to reduce the installed filtration area.

FIG. 11 Schematically shows the bottom view of the main outlet (14), the outlet fixed collector (2) with the outlet distributor flow channel (6) and the outlet vent (16) and depressurization port (20). A rotating outlet header (4) with outlet ports (18) is installed around the outlet fixed collector (2). The outlet housing (8) and the filter element housing (12) in which the filter element (s) (11) are located are affixed to the rotating outlet header (4). Plugs (19) serve to block the flow to the outlet ports (18) so that some of the housing subassemblies (8,11,12) can be removed to reduce the installed filtration area.

FIG. 12 Schematically shows the top view of the main inlet (13), the inlet fixed distributor (1) with the inlet distributor flow channel (5) and the inlet bleed (15). A rotating inlet header (3) with inlet ports (17) and oval port (21) is installed around the inlet fixed distributor (1). The inlet housing (7) and the filter element housing (12) in which the filter element (s) (11) are located are affixed to the rotating inlet header (3). In this case, the inlet housing (7) and filter element housing (12) are replaced with larger ones to hold more filter elements (11) in order to increase the installed filtration area.

FIG. 13 Schematically shows the bottom view of the main outlet (14), the outlet fixed collector (2) with the outlet distributor flow channel (6) and the outlet vent (16) and depressurization port (20). A rotating outlet header (4) with outlet ports (18) is installed around the outlet fixed collector (2). The outlet housing (8) and the filter element housing (12) in which the filter element (s) (11) are located are affixed to the rotating outlet header (4). In this case, the outlet housing (8) and filter element housing (12) are replaced with larger ones to hold more filter elements (11) in order to increase the installed filtration area.

FIG. 14 Schematically shows the top view of the main inlet (13), the inlet fixed distributor (1) with the inlet distributor flow channel (5) and the inlet bleed (15). A rotating inlet header (3) with inlet ports (17) and oval port (21) is installed around the inlet fixed distributor (1). The inlet housing (7) and the filter element housing (12) in which the filter element (s) (11) are located are affixed to the rotating inlet header (3). Plugs (19) serve to block the flow to the inlet ports (17) so that some of the larger housing subassemblies (7,11,12), that were enlarged as shown in FIG. 12, can be removed to reduce the installed filtration area using the larger housings.

FIG. 15 Schematically shows the bottom view of the main outlet (1lt), the otítlet fixed co0çctprJ) with the outlet distributor flow channel (6) and the outlet vent (16) and depressurization port (20). A rotating outlet header (4) with outlet ports (18) is installed around the outlet fixed collector (2). The outlet housing (8) and the filter element housing (12) in which the filter element (s) (11) are located are affixed to the rotating outlet header (4). Plugs (19) serve to block the flow to the outlet ports (18) so that some of the larger housing subassemblies (8,11,12) that were enlarged as shown in FIG. 13 can be removed to reduce the installed filtration area using the larger housings.

FIG. 16 Schematically shows the top view of the main inlet (13), the inlet fixed distributor (1) with the inlet distributor flow channel (5) and the inlet bleed (15). A rotating inlet header (3) with inlet ports (17) and oval port (21) is installed around the inlet fixed distributor (1). The inlet housing (7) and the filter element housing (12) in which the. filter element (s) (11) are located are affixed to the rotating inlet header (3). In this view, one housing subassembly (7,11,12) is shown to be normally in the stand-by mode. This is achieved by reducing the length of the inlet distributor flow channel (5).

FIG. 17 Schematically shows the bottom view of the main outlet (14), the outlet fixed collector (2) with the outlet distributor flow channel (6) and the outlet vent (16) and depressurization port (20). A rotating outlet header (4) with outlet ports (18) is installed around the outlet fixed collector (2). The outlet housing (8) and the filter element housing (12) in which the filter element (s) (11) are located are affixed to the rotating outlet header (4). In this view, one housing subassembly (8,11,12) is shown to be normally in the stand-by mode. This is achieved by reducing the length of the outlet distributor flow channel (6).

FIG. 18 Schematically shows the top view of the main inlet (13), the inlet fixed distributor (1) with the inlet distributor flow channel (5) and the reverse-flow outlet (22). A rotating inlet header (3) with inlet ports (17) is installed around the inlet fixed distributor (1). The inlet housing (7) and the filter element housing (12) in which the filter element (s) (11) are located are affixed to the rotating inlet header (3).

FIG. 19 Schematically shows the bottom view of the main outlet (14), the outlet fixed collector (2) with the'outlet distributor flow channel (6). A rotating outlet header (4) with outlet ports (18) is installed around the outlet fixed collector (2). The outlet housing (8) and the filter element housing (12) in which the filter element (s) (11) are located are affixed to the rotating outlet header (4).

FIG. 20 Schematically shows the top view of the main inlet (13), the inlet fixed distributor (1) with the inlet distributor flow channel (5) and the reverse-flow outlet (22). A rotating inlet header (3) with inlet ports (17) is installed around the inlet fixed distributor (1). The inlet housing (7) °and the filter element housing (12) in which the filter element (s) (11) are located are affixed to the rotating inlet header (3).

In this reverse-flow case, a specific portion of the clean filtrate is allowed to flow in the reverse direction through the filter element (s) (11) for cleaning purposes. The filtrate portion, being used for cleaning, exits through the reverse-flow outlet (22).

FIG. 21 Schematically shows the bottom view of the main outlet (14), the outlet fixed collector (2) with the outlet distributor flow channel (6). A rotating outlet header (4) with outlet ports (18) is installed around the outlet fixed collector (2). The outlet housing (8) and the filter element housing (12) in which the filter element (s) (11) are located are affixed to the rotating outlet header (4). In this reverse-flow case, a specific portion of the clean filtrate is allowed to flow from the outlet fixed collector (2), in the reverse direction through the filter element (s) (11) for cleaning purposes.

FIG. 22 Schematically shows the bottom view of the main outlet (14), the outlet fixed collector (2) with the outlet distributor flow channel (6) and the reverse-flow inlet (23). A rotating outlet header (4) with outlet ports (18) is installed around the outlet fixed collector (2). The outlet housing (8) and the filter element housing (12) in which the filter element (s) (11) are located are affixed to the rotating outlet header (4).

FIG. 23 Schematically shows the bottom view of the main outlet (1', 4) the odleFfixed cot tofO w7th the outlet distributor flow channel (6). A rotating outlet header (4) wfth oiAlbet ports (18) is installed around the outlet fixed collector (2). The outlet housing (3) and the filter element housing (12) in which the filter element (s) (11) are located are affixed to the rotating outlet header (4). In this reverse-flow case, a suitable liquid is allowed to flow from the reverse flow inlet (23) in the reverse direction through the filter element (s) (11) for cleaning purposes.

FIG. 24 Schematically shows the filter system with a main inlet (13) and a main outlet (14). Attached to the main inlet (13) and main outlet (14) is the combined rotating inlet and outlet headers (3,4) with inlet ports (17) and outlet ports (18), and the combined inlet fixed distributor and outlet fixed collector (1,2) with inlet distribution flow channel (5) and outlet distributor flow channel (6).

The above figures illustrate the simple design of the element filter housing (12), which is basically a cylinder with one small, or one large hole to hold multiple filter elements (11). The invention covers similar designs where multiple holes for individual filter elements (11) may be provided in the element filter housing (12) to streamline the flow and minimize the residence time and its distribution. The invention covers similar designs with multiple concentric circles just the same. Also, the above figures show the filter element (11) as a cartridge type filter element; the invention covers filter systems with differently shaped filter elements just the same. For example, a stack of filter discs could be used in every single element filter housing (12).

To further illustrate the procedure to renew the filter area, the procedure is as follows while referring to figures 1 through 10: When a specific condition such as the differential pressure over the filter system indicates that a change of filter area is required, the rotatable filter assembly is rotated so that one housing subassembly (7,8,12) is isolated from the flowing product and in turn gets depressurized through the depressurization port (20). Then the housing subassembly (7,8,12) is either removed for remote servicing or is serviced on the filter ; in either case the filter element (s) (11) would be replaced with clean one. All along, the product is still flowing. After the service completion, the rotatable filter assembly is rotated further to the one and only bleeding and venting position of the filter, so that the newly serviced housing subassembly (7,8,12) can be filled with product by bleeding through the inlet bleeding port (15) and vented through the outlet vent (16). Then, the rotatable filter assembly is rotated further in order to return the newly serviced housing subassembly (7,8,12) into the filtration service. The rotation cycle would then be repeated for the service of the remaining housing subassemblies (7,8,12). Again, all along the complete rotation cycle, there is no interruption of product flow.

In the case of the reverse flow cleaning, the procedure is as follows while referring to figures 18 through 23: When a specific condition such as the differential pressure over the filter system indicates that the cleaning of the filter elements is required, the rotatable filter assembly is rotated so that one housing subassembly (7,8,12) is isolated from the flowing product on the inlet side only at the reverse-flow port (22). A part of the filtrate being, or another suitable liquid, under pressure flows from the outlet fixed collector or reverse flow inlet, in the reverse direction through the filter element (s) (11) and exits via the reverse-flow port (22). After an appropriate period of time and the cleaning completion, the rotatable filter assembly is rotated further in order to return the newly cleaned housing subassembly (7,8,12) into the filtration service. The rotation cycle would then be repeated for the cleaning of the remaining fitter elements (11). All along the complete rotation cycle, there is no interruption of product flow.