Self-cleaning fuel oil strainer Number:6,821,444 from the United States Patent and Trademark Office (PTO) owispatent

Title: Self-cleaning fuel oil strainer

Abstract: A self-cleaning fuel oil strainer, coupled to a continuous fuel flow, that includes a pair of canisters, each having a cylindrical wedge wire fuel oil filter screen. An elongated brush running the length of the screen is disposed between two confining walls also running the length of the screen to form a chamber. A elongated partition, including two sets of apertures, is used, along with the elongated brush, to divide the chamber into two particulate dislodge chambers and a drain subchamber. A drain is in fluid communication with the drain subchamber. During cleaning, the drain is opened and the screen is rotated against the brush for liberating the particulate contaminants and a limited amount of fuel oil into the two dislodge subchambers. The particulate contaminants and the limited amount of fuel oil then pass through the apertures at a high velocity and into the drain subchamber which exits through the drain. Alternatively, a reverse flow of clean fuel oil can be used in combination with the elongated brush, for dislodging the particulate contaminants from the fuel oil filter screen. Finally, another variation of using a reverse flow of clean fuel oil for cleaning purposes is discussed whereby a stationary fuel oil strainer is disposed in a system that isolates the fuel oil strainer from the normal fuel oil flow during cleaning.

Patent Number: 6,821,444 Issued on 11/23/2004 to Benenson, Jr.,   et al.

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Inventors:	Benenson, Jr.; James (New York, NY); Laing; David A. (Elyria, OH)
Appl. No.:	283645
Filed:	October 30, 2002

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Related U.S. Patent Documents

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	Application Number	Filing Date	Patent Number	Issue Date
	937411	Dec., 2000	6517722
	417404	Oct., 1999	6177022
	014447	Jan., 1998

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Current U.S. Class:	210/785 ; 210/408; 210/411; 210/791
Field of Search:	210/333.01,342,388,408,411,412,456,457,458,489,499,323.2,422,785,791

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Primary Examiner: Savage; Matthew O.
Attorney, Agent or Firm: Caesar, Rivise, Bernstein, Cohen & Pokotilow, Ltd.

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Parent Case Text

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RELATED APPLICATIONS

This application is a Continuation of application Ser. No. 09/737,411, filed on Dec. 15, 2000, (now U.S. Pat. No. 6,517,722) which is entitled SELF CLEANING FUEL OIL STRAINER, which is a Continuation-in-part of application Ser. No. 09/417,404, filed on Oct. 13, 1999 (now U.S. Pat. No. 6,177,022) which is a Continuation-in-part of Co-pending application Ser No. 09/014,447 filed Jan. 28, 1998, the latter of which is now abandoned, all of which are entitled SELF-CLEANING FUEL OIL STRAINER, and all of whose entire disclosures are incorporated by reference herein.

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Claims

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We claim:

1. A strainer for removing particulates from a fluid flow, said strainer comprising: a stationary cylindrical porous member disposed in the fluid flow and having a first outer surface upstream of the flow and a second inner surface downstream of the flow, the particulates lodging against said first outer surface, said stationary cylindrical porous member defining an inner region; a single ultrasonic energy source contained within a housing, wherein said ultrasonic energy source and housing are positioned inside said inner region adjacent said second inner surface for dislodging particulates from said first outer surface; and means for backwashing that convey a reverse flow of a clean fluid from said second inner surface through said first outer surface to evacuate said dislodged particulates from returning to said first outer surface.

2. The strainer of claim 1 wherein said means for backwashing operates without the use of a nozzle.

3. The strainer of claim 1 wherein said clean fluid comprises said fluid flow that has already passed through said second inner surface.

4. A method for removing particulates from a strainer positioned in a first fluid flow having particulates therein, said method comprising the steps of: disposing a first outer surface of a stationary cylindrical porous member in the first fluid flow to capture particulates against said first outer surface; positioning a housing containing a single ultrasonic energy source within an inner region of said stationary cylindrical porous member defined by a downstream second inner surface of said stationary cylindrical porous member, said second inner surface permitting passage of a cleaned fluid flow; isolating said stationary cylindrical porous member from said first fluid flow; activating said ultrasonic energy source to dislodge particulates from said first outer surface; and sending a reverse flow of a clean fluid through said second inner and first outer surfaces to evacuate said dislodged particulates from returning to said first outer surface.

5. The method of claim 4 wherein said step of sending a reverse flow of a clean fluid comprises sending a reverse flow of said first fluid flow that has already passed through said second surface.

6. A method for reducing the amount of cleaned fluid required in cleaning a particulate strainer using a reverse flow system, said method comprising the steps of: disposing a stationary cylindrical strainer in a first fluid flow to capture particulates against a first upstream surface of the strainer; positioning a housing containing a single ultrasonic energy source within an inner region of said stationary cylindrical strainer defined by a downstream second surface, said second surface permitting passage of a cleaned fluid flow; stopping said first flow; activating said ultrasonic energy source to dislodge particulates from said first surface; sending a reverse flow of said cleaned fluid flow through said second surface and through said first surface to evacuate said dislodged particulates from returning to said first surface; and restoring the passage of said first flow through said strainer.

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Description

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BACKGROUND OF THE INVENTION

This invention relates generally to filter devices and, more particularly, to fuel system filters for small particulate contaminants.

It is well-known that the mechanical cleaning of a filter surface can be accomplished by having a brush or scraper drag along the filter surface where deposits have accumulated. In certain configurations, the brush or scraper is mounted at one end between two walls but with a significant portion of the brush or scraper projecting beyond the walls. Such configurations are shown in U.S. Pat. No. 148,557 (Gillespie et al.); U.S. Pat. No. 556,725 (Farwell); U.S. Pat. No. 740,574 (Kohlmeyer) and U.S. Pat. No. 793,720 (Godbe). In conventional filter systems, the particulate contaminants are driven off the filter surface and are deposited in a hopper or tank along with the fluid being filtered, thus discarding large amounts of the fluid being filtered.

The use of a brush, or high speed cleaning spray, disposed between a pair of walls for cleaning a cylindrical filter is known in the art, as is disclosed in U.S. Pat. No. 5,423,977 (Aoki et al.) and U.S. Pat. No. 5,595,655 (Steiner et al.) and Swiss Patent No.22,863 (Zingg). Another variation employs a backwash that drives the particulate contaminants off of the cylindrical filter, as is disclosed in U.S. Pat. No. 3,338,416 (Barry).

One desirable use for fuel oil filter systems of the present invention is in ships. Prior art ship fuel oil systems use conventional filter cartridges for cleaning the fuel in-line. However, these filter cartridges require frequent replacement which, in turn, requires the fuel flow to be interrupted during replacement. Interruption of the fuel oil flow will shut down the ship's main engines, thereby rendering the ship incapable of maneuvering. This can be catastrophic where the ship is in tight quarters, e.g., during docking or navigating through narrow passageways, or during storms, or during battle with regard to warships.

Furthermore, there are additional costs of having to store sufficient replacement cartridges onboard, the logistics involved in shipping and disposing the cartridges to and from the ship, and the labor costs involved in replacing the cartridges.

In addition, shipboard fuel oil straining is a specialized straining process. In particular, the fuel oil flow is initially pre-strained for gross particulate contaminants, such that any particulate contaminants remaining in the fuel oil flow are extremely small (e.g., <100 microns, with a large percentage being less than 25 microns). As a result, where these small particulate contaminants are captured by a downstream strainer (e.g., a wedge wire screen strainer), both on and within the strainer surface, and then later dislodged during the strainer cleaning process, these extremely small particulate contaminants do not fall by gravity toward a drain but remain suspended in the fuel oil and will re-attach to the strainer surface. Therefore, there remains a need for a cleaning device that can dislodge such extremely small particulate contaminants off of the downstream strainer surface, as well as from within the strainer surface, and then ensure that these particulate contaminants flow out through the drain rather than re-attaching to the strainer surface.

Thus, there is a need for an improved system for removing undesired particulate contaminants from a fuel oil flow and without interrupting that fuel oil flow to the engines, while minimizing the amount of fluid removed therewith. It is to just such a system that the present invention is directed.

OBJECTS OF THE INVENTION

Accordingly, it is the general object of the instant invention to provide a fuel oil cleaning device that overcomes the problems of the prior art.

It is a further object of this invention to provide a fuel oil cleaning device that permits continuous fuel oil flow even during the cleaning process.

It is a further object of this invention to provide a fuel oil cleaning device that removes small particulate contaminants from a strainer surface, and from within the strainer surface, and ensures that when these small particulate contaminants are dislodged from the strainer during cleaning that they enter a drain rather than re-attaching to the strainer surface.

It is still yet another object of this invention to provide a fuel oil cleaning device that generates a high velocity flow of dislodged particulate contaminants away from the strainer and into a drain.

It is a further object of this invention to provide a fuel oil cleaning device that minimizes the amount of fuel oil that must be discarded during cleaning.

It is still yet a further object of this invention to eliminate the need for frequent replacement of the fuel oil filter.

It is still another object of this invention to minimize the costs associated with frequent fuel oil filter replacements.

It is still yet even another object of this invention to improve the efficiency of particulate removal.

It is still yet another object of this invention to provide a fuel oil filter that can be self-cleaned with the use of a reverse flow of clean fuel oil.

It is even yet another object of this invention to provide a self-cleaning fuel oil filter system that permits the fuel oil filter element to remain stationary during cleaning.

SUMMARY OF THE INVENTION

These and other objects of the invention are achieved by providing a fuel oil cleaning system disposed within a fuel oil flow having particulate contaminants therein. As mentioned earlier, the particulate contaminants that need to be removed from the fuel oil flow are extremely small, less than 100 microns, and a large percentage of these less than 25 microns, therefore do not settle out by gravity. The invention of the present application is well-suited to removing these small particulate contaminants from the fuel oil flow and into a drain.

The fuel oil cleaning system comprises: an inlet valve for controlling the fuel oil flow having particulate contaminants therein which forms a contaminated fuel oil flow and wherein the contaminated fuel oil flow flows through a first output port of the inlet valve; a stationary porous member positioned in the contaminated fuel oil flow that passes through the first output port and wherein the contaminated fuel oil flow enters the stationary porous member through a first porous member surface and exits through a second porous member surface towards a second output port; and wherein the contaminated fuel oil flow deposits the particulate contaminants on the first porous member surface to form a clean fuel oil flow that flows toward the second output port; an outlet valve coupled to the second output port for controlling the clean fuel oil flow; a flow control means, operated during a porous member cleaning process, having a flow control means input coupled to a source of clean fuel oil and a flow control means output coupled to the second output port; and wherein the flow control means controls a reverse flow of the clean fuel oil that flows from the second porous member surface through the first porous member surface for dislodging the particulate contaminants from the first porous member surface to form a contaminated reverse flow of fuel oil; a drain valve coupled to the first output for directing the contaminated reverse flow of fuel oil towards a drain during the cleaning process; and wherein the inlet valve and outlet valve are closed during the cleaning process.

The above invention also includes a method for cleaning a fuel oil flow having particulate contaminants therein. The method comprises the steps of: positioning a stationary porous member in the contaminated fuel oil flow such that the contaminated fuel oil flow enters the stationary porous member through a first porous member surface and exits through a second porous member surface toward an output port, and wherein the contaminated fuel oil flow deposits the particulate contaminants on the first porous member surface; isolating the stationary porous member from the contaminated fuel oil flow during a cleaning process; passing a reverse flow of clean fuel oil from the output port and through the stationary porous member from the second porous surface member surface to the first porous member surface for dislodging the particulate contaminants from the first porous member surface to form a contaminated reverse flow of fuel oil; opening a drain to receive the contaminated reverse flow of fuel oil; discontinuing the reverse flow of clean fuel oil while closing the drain to complete the cleaning process; and recoupling the stationary porous member to the contaminated fuel oil flow.

Another embodiment of the present invention comprises a fuel oil cleaning system for use with a fuel oil flow having particulate contaminants therein and wherein the cleaning system comprises: an inlet valve for controlling the fuel oil flow having particulate contaminants therein forming a contaminated fuel oil flow and wherein the contaminated fuel oil flows through a first output port of the inlet valve; a stationary porous member positioned in the contaminated fuel oil flow that passes through the first output port and wherein the contaminated fuel oil flow enters the stationary porous member through a first porous member surface and exits through a second porous member surface towards a second output port and wherein the fuel oil flow deposits the particulate contaminants on the first porous member surface to form a clean fuel oil flow that flows towards the second output port; a third output port coupled to a drain through a drain valve; the inlet valve being closed while the drain valve is opened during a cleaning process for generating a reverse flow of the clean fuel oil that flows from the second output port towards the third output port, and wherein the reverse flow of the clean fuel oil flows through the stationary porous member from the second porous member surface through the first porous member surface for dislodging the particulate contaminants from the first porous member surface to form a contaminated reverse flow of fuel oil that flows into the drain; and the drain valve being closed and the inlet valve being opened after the cleaning process is completed.

DESCRIPTION OF THE DRAWINGS

Other objects and many of the intended advantages of this invention will be readily appreciated when the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is a block diagram of the fuel oil system in which the present invention is located;

FIG. 2 is a top view of the present invention;

FIG. 3 is a partial side view of the present invention;

FIG. 4 is a bottom view of the present invention;

FIG. 5 is a cross-sectional view of the present invention taken along line 5--5 of FIG. 2;

FIG. 6 is partial sectional view taken along line 6--6 of FIG. 5;

FIG. 7 is a partial sectional view taken along line 7--7 of FIG. 5;

FIG. 8 is a cross-sectional view of the present invention using a reverse flow of clean fuel oil as part of the particulate-removing means;

FIG. 9 is a partial sectional view taken along line 9--9 of FIG. 8;

FIG. 10 is similar to FIG. 9 except that a different reverse flow direction is depicted;

FIG. 11 is an enlarged, cross-sectional view of a portion of FIG. 5, depicting different portions of the partition and one of the associated wipers;

FIG. 12 is an enlarged, cross-sectional view of a portion of FIG. 5, depicting the passageways in the particulate-removing means support for use with the alternative drain configuration;

FIG. 13 is a partial isometric view of the internal particulate chamber depicting the partition and one of the wipers comprising the shoes;

FIG. 14 is a schematic of a fuel oil cleaning system using a stationary fuel oil strainer;

FIG. 15 is a variation of the fuel oil cleaning system of FIG. 14 wherein the downline fuel flow is used as the source of the reverse clean oil fuel flow;

FIG. 16 is another variation of the invention of FIG. 15;

FIG. 17 is a cross-sectional view of a stationary filter, that can be used in the systems shown in FIGS. 14-16, and having an ultrasonic generator disposed therein;

FIG. 18 is an enlarged view of the circled portion shown in FIG. 17; and

FIG. 19 is a sectional view of the stationary filter taken along line 19--19 of FIG. 17.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following is a detailed description of the present invention. The present invention has wide application where straining very small particulate contaminants, less than 100 microns and large percentage of these are less than 25 microns, from a fuel oil flow is required, and is not limited to the environment shown in FIG. 1, as will be discussed in detail below. The present invention is characterized as a non-disposable cleaning device, i.e., having a porous member that can be cleaned rather than being thrown away. The term non-disposable is defined as an item that does not require periodic replacement, e.g., once a day, week or month. Thus, such a non-disposable item has obvious advantages in environments where storage is limited and cleaning device replenishment facilities are unavailable, e.g., ocean-going vessels. Other example systems include power plants, cogeneration facilities, etc.

As an exemplary environment, Applicants have depicted a ship fuel oil system for disclosing the preferred embodiment. Referring now in greater detail to the various figures of the drawing, wherein like reference characters refer to like parts, there is shown in FIG. 1 at 20 an oil strainer of the present invention. The oil strainer 20 forms part of a compensated fuel system for use on watercraft, e.g., ships and boats. The compensated fuel oil system comprises a fuel oil service subsystem which includes a service tank 24 which is filled daily from a main fuel storage tank 22 with approximately one day's amount of fuel. The flow of fuel from the service tank 24 to the engine (which in the preferred embodiment is either a gas turbine or a diesel engine) must be a continuous fuel oil flow, as defined above, in that any interruption in that flow will shut down the main engines of the ship, thereby rendering the ship incapable of maneuvering. As such, there cannot be any shutdown of the flow, even to clean a fuel oil filter located therein. To meet this requirement, the self cleaning fuel oil strainer 20 provides the means for filtering such a continuous fuel oil flow without interrupting that flow, as will be discussed below in detail.

As shown more clearly in FIG. 2, the fuel oil strainer 20 comprises two canisters 26 and 28 that are fed fuel oil from a common input manifold 30 (e.g., 21/2 inch class 150 ANSI flanged input) at the top portion of the strainer 20. Each canister 26 and 28 has two inputs from the common manifold 30, as indicated by inputs 32A and 32B for canister 26 and by inputs 34A and 34B for canister 28. Each canister 26 and 28 comprises a cylindrical-shaped porous member 36 and 38, respectively, through which the fuel oil flows, as will be discussed in detail later. The porous members 36 and 38 comprise a screen selected from the group consisting of wedge wire, wire cloth and perforated metal. In the preferred embodiment, the porous members 36 and 38 comprise wedge wire screens, such as those manufactured by Leem Filtration Products, Inc. of Mahwah, N.J. It is also within the broadest scope of the present invention that the porous members 36 and 38 may comprise wire cloth or perforated metal, as opposed to wedge wire screens. One of the main features of the oil strainer 20 is its ability to filter out fine particulate matter, e.g., particulates less than 100 microns, where a large percentage of these are less than 25 microns.

Drive mechanisms 40 and 42 (FIG. 3) are provided to rotate the respective porous members 36 and 38 during the cleaning process about their respective center axes, only one (44) of which is clearly shown in FIG. 5. Otherwise, during normal operation, the porous members 36 and 38 remain stationary.

As can be seen in FIG. 2, fuel oil enters each canister through its respective inputs and then flows around the periphery of each porous member 36 and 38; in particular, fuel oil flow from inputs 32A and 32B are shown by arrows 46A and 46B, respectively, and fuel oil flow from inputs 34A and 34B are shown by arrows 48A and 48B, respectively. The inputs 32A and 32B are located on both sides of an internal particulate chamber 50 (FIG. 7, which comprises two dislodge subchambers 50A/50B and a drain subchamber 50C, all of which are discussed later) in canister 26; similarly, although not shown, the inputs 34A and 34B in canister 28 are also located on both sides of a internal particulate chamber, also comprising two dislodge subchambers and a drain subchamber. Thus, fuel oil input flow moves away from the chamber 50 and around the periphery of the porous members 36 and 38 and then through them, as is discussed next.

Fuel oil flow through the porous member is more easily depicted in FIG. 5, which is a cross-sectional view of the canister 26, although it should be understood that the following discussion is applicable to the other canister 28. The main fuel oil flow is through the porous member 36, from an outside surface 37 to an inside surface 39, as indicated by the arrows 52, and down through the hollow interior 41 of the porous member 36. As the fuel oil then flows through the porous member 36, particulate contaminants are then trapped against the outer surface 37 of the porous member 36. The filtered fuel oil exits into a main output 54 of the canister, as shown by the arrow 56. FIG. 4 is a bottom view of both canisters 26 and 28 and it shows the main output 54 of canister 26 and a main output 58 of canister 28 feeding into a common output manifold 60. Thus, fuel oil flow through the strainer 20 is basically continuous.

When cleaning of the porous member 36 and 38 is required, as indicated by pressure drop across the strainer 20 (as measured by a pressure transducer, not shown), the drive mechanisms 40 and 42 are activated to rotate the respective porous members. In addition, solenoid valves 72 and 74 (FIG. 3) are activated to open respective drains (only one 76 of which is shown in FIG. 5), located directly below the drain subchamber 50C, for diverting the particulate debris and a limited amount fuel oil down through a respective drain, rather than through the main outlets 54 and 58. Furthermore, it is within the broadest scope of this invention to include other alternative locations for the drain, e.g., along the chamber, rather than under it, as will be discussed in detail later. Opening of the drain 76 (or the alternative drain) is kept to a minimum to discard as little fuel as possible while flushing the particulate contaminants from the chamber. Thus, for example, the drain 76 can be open all or any part of the time that the porous members 36 and 38 are rotating.

Cleaning of the porous members 36 and 38 is accomplished by the particulate-removing means, only one of which is shown most clearly in FIGS. 5, 7, 8 and 9; as such, the following discussion applies to the particulate-removal means in the canister 28 also. In the preferred embodiment, the particulate-removing means comprises an elongated wire brush 62 that spans the length of the porous member 36. The brush fibers are in contact with the outside surface 37 of the porous screen 36 and thus bear on the outside surface 37 of the porous member 36 along its entire length. The brush 62 forms the separation between the two dislodge subchambers 50A and 50B, while the majority of a brush support 63 is disposed inside the drain subchamber 50C, as shown in FIG. 7.

As mentioned previously, the chamber 50 comprises the two dislodge subchambers 50A/50B and a drain subchamber 50C. The chamber 50 comprises a pair of confining walls 64A and 64B, also running the length of the porous member 36, that enclose the brush 62/brush support 63. The purpose of these walls 64A and 64B is to contain the dislodged particulate debris within the chamber 50 so that substantially only fuel oil within this chamber 50 will be discharged through the drain 76 (or alternative drain 300, to be discussed later) during cleaning. A partition 200, also running the length of the porous member 36, forms the separation between the two dislodge subchambers 50A/50B and the drain subchamber 50C. The partition 200 itself comprises a pair of outer flanges 202A/202B, a base wall 204 and sidewalls 206A/206B. The base wall 204 is secured between a particulate-removing means (e.g., brush 62 or scraper) head 61 and the particulate-removing means support 63. At the bend between the sidewalls 206A/206B and the outer flanges 202A/202B, the partition 200 comprises a plurality of apertures 212 (FIGS. 7, 9, 11 and 12) that permit the passage of dislodged particulate contaminants from the two dislodge subchambers 50A/50B to the drain subchamber 50C. Because of the size of the apertures 212 (e.g., 0.094" diameter), once any particulate contaminants from the two dislodge subchambers 50A/50B make their way through the partition 200, there is very little chance that such particulate contaminants can find their way back through the apertures 212 and ultimately return to the outer surface 37.

A drain passageway 75, through a strainer support housing 77, is also shown in FIG. 5. FIGS. 7 and 9 also show the passageway 75 in phantom.

At the extreme ends of the confining walls 64A and 64B, respective wipers 65A and 65B are secured to the outside surfaces of the walls 64A and 64B, respectively, and which also run the length of the porous member 36. The wipers 65A and 65B (e.g., 316 stainless steel, half-hard) are coupled to the ends of the walls 64A and 64B using fasteners 78 and plates 79. As can be seen most clearly in FIG. 13, wiper 65A comprises a plurality of spaced-apart shoes or runners 67 that are in contact with the outer surface 37 of the porous member 36. These shoes 67 (e.g., 0.010"-0.015" thickness and 1/4" wide and which may be spot-welded to the wiper 65A) serve to maintain the wiper 65A a sufficient distance away from the outer surface 37 such that during cleaning, while the porous member 36 is rotating (direction of rotation is shown by the arrow 161 in FIG. 7), the particulate contaminants adhering to the outer surface 37 pass beneath the wiper 65A between the shoes and then are driven off of the outer surface 37 by the particulate-removing means 62 and into the dislodge subchamber 50A. The drain subchamber 50C is in direct fluid communication with the drain 76 (or alternative drain 300). When the drain 76 (or alternative drain 300) is open, any particulate contaminants suspended in the dislodge subchamber 50A are pulled toward the apertures 212 in the partition 200 and pass through them and out to the drain 76 (or 300).

Any remaining particulate contaminants which cannot be mechanically driven off of the surface 37 by the brush 62, e.g., particulate contaminants lodged in between the outer surface 37 and the inside surface 39 of the porous member 36 (e.g., lodged in the wedge wire cells of a porous member 36 comprising wedge wire), are subjected to a reverse pressure and are driven out of the surface 37 into the second dislodge subchamber 50B. In particular, unlike the first dislodge subchamber 50A which is not totally closed off since the wiper 65A stands off from the outside surface 37 of the porous member 36, the second dislodge subchamber 50B forms a completely-closed off chamber because the wiper 65B does not include shoes and, therefore, is in contact with the outer surface 37 along its entire length. Thus, the second dislodge subchamber 50B is subjected completely to the influence of the pressure differential created between the inside surface 39 of the porous member 36 and the opened drain pressure which is present in the drain subchamber 50C, via the apertures 212. When the drain 76 (or 300) is open, these particulate contaminants, lodged in between the outer surface 37 and the inside surface 39 of the porous member 36, are driven out of that region by the reverse pressure differential and then are suspended in the second dislodge subchamber 50B; this pressure differential also pulls these particulate contaminants toward the apertures 212 in the partition 200 and into the drain subchamber 50C for passage through the drain 76 (or 300).

As pointed out earlier, the particulate contaminants are of an extremely small size, less than 100 microns, and a large percentage of these are less than 25 microns; as a result, these particulate contaminants do not settle out by gravity into the drain but rather, due to their small size, remain suspended in the fuel oil. The invention of the present application is well suited to overcome this problem as described below.

It should be understood that the apertures 212 provide for fluid communication between the first dislodge subchamber 50A and the drain subchamber 50C and for fluid communication between the second dislodge subchamber 50B and the drain subchamber 50C. However, because the apertures 212 are small, they maintain a high velocity of particulate contaminants from both the first and second dislodge subchambers 50A and 50B into the drain subchamber 50C under the influence of the reverse pressure differential. Such a high velocity cannot be sustained by replacing the apertures 212 with a slot. Furthermore, replacing the apertures 212 with a slot would defeat the purpose of maintaining the transferred particulate contaminants (i.e., particulate contaminants that have passed from the dislodge subchambers 50A/50B) in the drain chamber 50B since the particulate contaminants would not be precluded from making their way back to the outer surface 37 of the porous member 36.

In particular, the advantage of using the plurality of apertures, as opposed to a slot of the type shown in U.S. Pat. No. 5,595,655 (Steiner et al.), is that the plurality of apertures provides for a rapid flow velocity as opposed to a low flow velocity for the slot. For example, if there are 21 apertures that form one set of apertures in the partition 200, each having a diameter of approximately 0.094", then the total area is approximately .pi.(0.094"/2).sup.2.times.21=0.1457 in.sup.2. If, on the other hand, a slot having a width of 0.094" and a length of 12.594" (i.e., the length from the top of the uppermost aperture in the partition 200 to the bottom-most aperture in the partition 200; this is a reasonable assumption since the Steiner et al. patent states that the slot is substantially equal to the scraper length-Steiner et al. patent, col. 1, lines 61-62) is used, the area is 1.184 in.sup.2. Thus, using a plurality of apertures presents only 1/8 the area of the slot. As a result, for a given flow rate (gallons/minute), the slot may provide flow velocity of 1 ft/sec whereas the apertured partition generates a flow velocity of 8 ft/sec. The higher velocity significantly reduces the chance that a particulate will migrate backwards through the plurality of apertures and re-attach to the porous surface 36.

It is also within the broadest scope of the present invention to include an alternative drain