In-tank return line filter element and hydraulic reservoir with same

A top or bottom mounted, in-line, in-tank return line filter element is mounted in a hydraulic reservoir. The reservoir includes a holding tank, at least one outlet extending from and one return line extending to the reservoir, an in-tank return line within the reservoir and extending to one return line, and an in-tank return line filter element mounted within the in-tank return line. The in-tank return line filter element includes an end cap, a filter media and a by-pass valve coupled thereto. The end cap includes a central fluid opening, a mounting surface for the filter media, and a peripheral attaching mechanism for attaching the filter element to the in-tank return line to form a filter assembly. The mounting surface is positioned between the central opening and the attaching mechanism such that an in-line, in-tank filter element is provided.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an in-tank return line filter element. Specifically, the present invention relates to an in-tank return line filter elements and hydraulic reservoirs that incorporate the respective filter elements.

2. Background Information

Hydraulic reservoirs are used to hold hydraulic fluid that can be utilized by hydraulic systems, such as used in heavy machinery, including cranes, backhoes, demolition shears, bulldozers, and the like. In hydraulic systems, it is important to keep the hydraulic fluid free of debris. Consequently, filter units or filter assemblies have been incorporated in the hydraulic systems to filter debris from the hydraulic fluid.

U.S. Pat. Nos. 6,116,454; 6,475,380 and 6,508,271 disclose hydraulic reservoir designs that incorporate specific filter assemblies therein (i.e. in-tank filter elements), and these patents are incorporated herein by reference. The filter elements can be on the outlet lines, as shown in the '454 patent or in the inlet lines as shown in the '380 and '271 patents. A filter element on the outlet or suction side of a hydraulic reservoir is generally a simple strainer. Placing the filter element in the inlet or return lines that extends to the reservoir, as shown in the '271 and '380 patents provides certain advantages relating to the energy required by filtration and returning of the fluid to the reservoir.

The large majority of in-tank filter elements for hydraulic reservoirs utilize a return line filter element of some kind. One known or common example is a forming a partition or separate box structure within the hydraulic reservoir and incorporating a top mounted, or drop-in, filter element therein. A similar known configuration is to have the filter element as part of a larger filter assembly which is “dropped” into the top of the container with the return lines connected directly to the head of the filter assembly. This filter element is also a top mounted structure. The term “top mounted” refers to access or mounting direction in that the filter element is accessed and replaced through the top of the reservoir, such as in the '271 patent. These prior art top mounted filter elements result in a large amount of components and design complexity in the filter assembly due to sealing requirements and the like that are necessary.

There is a need in the industry for a simple, efficient, in-tank, in-line filter element for a return line of a hydraulic reservoir.

SUMMARY OF THE INVENTION

The problems set out above are solved by the hydraulic reservoirs having one of several in-tank return line filter elements according to the present invention. The hydraulic reservoir according to the invention includes a holding tank for holding fluid, at least one outlet from the hydraulic reservoir, at least one return line to the hydraulic reservoir, an in-tank return line extending within the hydraulic reservoir and extending to one return line, and an in-tank return line filter element mounted within the in-tank return line. The in-tank return line filter element is formed of an end cap, a filter media coupled to the end cap and a by-pass valve coupled to the filter media. The end cap includes a central opening for fluid, a mounting surface for attaching the filter media, and an attaching mechanism at a peripheral edge of the end cap for attaching the filter element to the in-tank return line. The in-tank return line and the filter element form a filter assembly for the hydraulic reservoir. The mounting surface is positioned between the central opening and the attaching mechanism such that an in-line, in-tank, filter element is provided.

These and other advantages of the present invention will be clarified in the description of the preferred embodiment taken together with the attached figures wherein like reference numerals represent like elements throughout.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1aillustrates a preferred embodiment of the present invention.FIGS. 1band1cillustrate modified embodiments of this invention. The scope and content of the present invention may best be elucidated by beginning with the “modified” form offigure 1cand following the evolution to the preferred embodiment. As discussed below, all of the specific embodiments are within the scope of the present claimed invention.

FIG. 1cis a schematic view of a hydraulic reservoir8(not shown completely) having an in-tank return line filter element10according to the present invention. The term “hydraulic reservoir” within the meaning of this application refers to a container for holding working fluid that is conveyed and returned to the reservoir in a circulating system or a holding container for a fuel. Generally, the working fluid is for hydraulic power or for lubrication such as petroleum and water-based fluids. The hydraulic reservoir8may be metal (e.g. steel) or plastic as known in the art. U.S. Pat. No. 6,508,271 discusses rotomolding of hydraulic reservoirs and is incorporated herein by reference. The hydraulic reservoirs8utilizing the present invention have one or more outlets for supplying hydraulic fluid contained in the reservoir to associated hydraulic systems as needed. Additionally the hydraulic reservoirs8include one or more return lines extending to hydraulic reservoir8, generally in the upper portion of the hydraulic reservoir8, for returning hydraulic fluid to the hydraulic reservoir. Within the meaning of this application a “return line” references that portion of the hydraulic circuit returning fluid to the hydraulic reservoir8that is exterior to the hydraulic reservoir8and the “in-tank return line” is that portion of the fluid circuit that is located within the hydraulic reservoir8. The hydraulic reservoir8is vented to atmosphere.

FIG. 1cis a sectional view of an in-tank return line for a hydraulic reservoir8having a “top mounted” filter element10according to a first embodiment of the present invention. The term “top mounted” within the meaning of this specification means that the filter element10will be withdrawn (i.e. replaced) in a direction opposite of the flow of the in-tank return line and the filter element10will be attached to the return line by moving the filter element10along the direction of the flow in the in-tank return line. The top mounted designs effectively allows the filter element10to be replaced without a separate access into the reservoir8and avoids any need to drain the reservoir8during replacement of the filter element10. The term “top mounted” is not intended to define a specific direction of the in-tank return line, which may extend from the top, bottom or side of the hydraulic reservoir8. The details of the hydraulic reservoir8are known in the art and are not described herein in detail.

The top mounted, in-tank return line filter element10includes a plastic end cap12coupled to an in-tank return line as described here and after. Plastic saves manufacturing and shipping costs (due to weight), but other suitable materials can be used. The end cap12includes a central opening14for receiving the hydraulic fluid through the filter element10and into the hydraulic reservoir8. The end cap12further includes a lower mounting surface16, an upper connection or hose barb17, attachment flats19and a peripheral threaded attachment surface18. The attachment surface18can include other associated configuration to assist in the attachment of the filter element10to the in-tank return line.

A filter media20is bonded to the mounting surface16such as through an epoxy or other conventional attachment techniques. The filter media20includes a filtering structure and a support tube providing structural support (i.e. a backbone) to the filter media20as is known in the art.

A mounting flange22is attached to a distal end of the filter element20opposite the end cap12. The mounting flange22allows for the attachment of a bypass valve assembly24. The bypass valve assembly24includes an extended valve housing26, a spring28and a valve body30.

The end cap12, a filter media20, mounting flange22and bypass valve assembly24combined to form the top mounted, in-tank return line filter element10according to the present invention. The in-tank return line filter element10is positioned within an in-tank return line that extends into the hydraulic reservoir8to form a filter assembly.

InFIG. 1cthe in-tank return line is formed by a half coupling38welded, or otherwise secured to the periphery of the reservoir8and a tubular in-tank return line enclosure portion40extending from the periphery of the hydraulic reservoir8. The threaded attachment surface18is threaded to corresponding threads of the coupling38. Although mounted on the exterior of the tank8, the coupling38is essentially a mounting plate for the filter element10and is effectively part of the in-tank return line. Any other suitable fitting or other mechanical connection may be utilized in place of the threads. The return line is secured to the coupling17of the end cap12in a conventional fashion, such as a hose clamp. When extending from an upper portion of the hydraulic reservoir8, the in-tank return line40may extend past the centerline of the reservoir8and preferably into a position well below the normal fluid level line within the hydraulic reservoir holding tank. This design will help avoid foaming within the fluid in the holding tank and will generally improve the fluid flow characteristics within the hydraulic reservoir8.

In operation the hydraulic fluid is returned to the hydraulic reservoir8through the return line and into the in-tank return line formed by filter element10, coupling38and first portion40. It will be apparent from a review ofFIG. 1that the in-tank return line, specifically the coupling38and first portion40, forms the housing for the filter element10, whereby the filter element10and the in-tank return line form a filter assembly. The returning hydraulic fluid will, normally, flow though opening14then through the filter media320into the hydraulic reservoir holding tank. This forms an inside out filter element that uses the return line pressure for filtration. In other words no additional work or energy is needed for the filtration process, and there is no additional drag on the system.

The bypass valve assembly24operates in a conventional manner as an emergency bypass. The spring28is set to a by-pass pressure. If the filter media20is close to reaching its capacity (i.e. it is clogged), the pressure in the in-tank return line will increase until it reaches the by-pass pressure of the spring28. At the by-pass pressure the spring28will be depressed by the valve body30allowing fluid to flow through openings (not shown) in the valve housing26to the reservoir interior. Activation of the by-pass valve assembly24by-passes the filter media20, as known in the art. The in-line, in-tank return line positioning of the filter element10allows for a simple by-pass valve alarm to be utilized. The hydraulic reservoir8holding tank is vented to atmosphere and will therefore be at atmospheric pressure. A simple pressure sensor (not shown) can be connected to the in-tank return line to measure in-tank return line pressure. An alarm or other indication can be set at, or slightly below the by-pass pressure to give warning of the by-pass activation. In other words the alarm can indicate that immediate maintenance is required. The standard maintenance will be the replacement of the filter element10.

The filter element10is designed for easy replacement and is top mounted relative to the in-tank return line. The replacement is exterior to the hydraulic reservoir8. The operator will release the hose clamp to disengage the return line from the coupling17of the end cap12of the filter element10. With the filter element10disengaged, the old filter element10can be removed and a new filter element10inserted. The new filter element10can be secured to the coupling38and the return line reattached to the coupling17. The “top mounting” can be more precisely defined as a mounting that attaches to the in-tank return line with the direction of flow and is disengaged in the direction opposite of the flow.

The filter element10can be used with a variety of existing hydraulic reservoirs8. All that is required is the presence of an in-tank return line sufficient for receiving the filter element10to form a filter assembly therein, and an appropriate mounting coupling38for attaching the filter element10. It is anticipated that the first portion40and coupling38may also be retrofitted onto existing hydraulic tanks8to utilize the filter element10.

FIG. 1billustrates a filter element110similar to the filter element10discussed above. The in-tank return line is formed of coupling138and portion140. The top mounted, in-tank return line filter element110includes a plastic end cap112coupled to the coupling38. The end cap112includes a central opening114for receiving the hydraulic fluid through the filter element110and into the hydraulic reservoir8. The end cap112further includes a lower mounting or sealing surface116, an upper connection or hose barb117, attachment flats119and a peripheral threaded attachment surface118. The attachment surface118can include other configurations (e.g. press snap tight fit) to assist in the attachment of the filter element110to the in-tank return line.

A filter media120is spring biased against a gasket121that is bonded to the mounting surface16. The filter media120includes a filtering structure and a support tube providing structural support (i.e. a backbone) to the filter media120as is known in the art. A mounting flange122is attached to a distal end of the filter element120opposite the end cap112. The mounting flange122allows for the attachment of a bypass spring124. The bypass spring124is mounted on base plate126that is secured to the end cap112though perforated tube128. One or more pins130in the cap112can be used to securely attach the perforated tube to the cap112.

The end cap112, a filter media120, mounting flange122and bypass spring124, base plate126and perforated tube128combined to form the top mounted, in-tank return line filter element110according to the present invention. The in-tank return line filter element110is positioned within an in-tank return line that extends into the hydraulic reservoir8to form a filter assembly.

The bypass assembly is formed by the biased filter media120which operates as an emergency bypass. The spring124is set to a by-pass pressure. If the filter media120is close to reaching its capacity (i.e. it is clogged), the pressure in the in-tank return line will increase until it reaches the by-pass pressure of the spring124. At the by-pass pressure the spring124will be depressed moving the filter media away from the sealing gasket121allowing fluid to flow through between the filter media120and the gasket121(and not through the media120) to the reservoir interior. The in-line, in-tank return line positioning of the filter element110also allows for a simple by-pass valve alarm to be utilized. As shown in the figure, the central opening14may include slots134to increase flow into the filter assembly.

FIGS. 1aand1dillustrate a filter element110′ according to a preferred embodiment of the present invention and is substantially similar to the filter element110discussed above. The only difference is that the perforated tube128and base plate126are replaced with plastic components. Specifically, tube128is replaced with plastic legs150that are formed integral with the end cap112. The integral formation of the legs150eliminates the pins130and the associated assembly step for the filter element offigure 1c. The legs150include locking projections152which can be used to secure the legs150to a plastic retaining plate154(which replaces the base plate126ofFIG. 1c). Locking slots156that receive the legs150and projections152there through are provided on the plate154as shown inFIG. 1d. One portion of the slot156is sized to receive the leg and the projection152, with the remaining portion of the slot156being smaller than the projection as will be generally understood by those of ordinary skill in the art. The filter element110′ is intended to reduce the manufacturing costs and total components of the filter assembly.

FIG. 3is a sectional view of an in-tank return line for a hydraulic reservoir8having a filter element210according to a second embodiment of the present invention. Additionally, as will become apparent, the hydraulic reservoir8will need to have a man-way opening, or clean out access6for replacement of the bottom mounted filter element210. The term “bottom mounted” within the meaning of this specification means that the filter element210will be withdrawn (i.e. replaced) in a direction of the flow of the in-tank return line and the filter element210will be attached to the return line by moving the filter element210along the direction opposite the flow in the in-tank return line. This is the opposite of the “top mounted” filter elements ofFIGS. 1a-dand2. As noted above, these terms are not intended to define a specific direction of the in-tank return line which may extend from the top, bottom or side of the hydraulic reservoir8. The additional details of the hydraulic reservoir8are known in the art and are not described herein in detail.

The bottom mounted, in-tank return line filter element210includes an end cap212coupled to an in-tank return line as described here and after. The end cap212includes a central opening214for receiving the hydraulic fluid through the filter element210and into the hydraulic reservoir8. The end cap212further includes an upper mounting surface216and a peripheral attachment surface218. As with “top mounted”, the terms “upper” and “lower” are not intended to define the orientation of the elements or the associated surfaces. The attachment surface218can include threads as shown inFIG. 3, or other associated configuration to assist in the attachment of the filter element210to the in-tank return line.

A filter media220is bonded to the mounting surface216such as through an epoxy or other conventional attachment techniques. The filter media220, similar to filter media20, includes a filtering structure and a support tube providing structural support (i.e. a backbone) to the filter media220as is known in the art.

A mounting flange222is attached to a distal end of the filter element220opposite the end cap212. The mounting flange222allows for the attachment of a bypass valve assembly224. The bypass valve assembly224includes an extended valve housing226, a spring228and a valve body230.

The end cap212, a filter media220, mounting flange222and bypass valve assembly224combined to form the bottom mounted, in-tank return line filter element210according to the present invention. The in-tank return line filter element210is positioned within an in-tank return line that extends into the hydraulic reservoir8to form a filter assembly.

InFIG. 3the in-tank return line is formed by a first return line portion240extending from the return line at the periphery of the hydraulic reservoir8. A coupling220may be provided for attachment of the external return line, with the coupling38being of any conventional fashion (i.e. it will match the specific return line). The first portion240includes threads242at a distal end thereof. As discussed above in connection withFIG. 1, when extending from an upper portion of the hydraulic reservoir8, the in-tank return line may extend past the centerline of the reservoir8and preferably into a position well below the normal fluid level line within the hydraulic reservoir holding tank.

The bottom mounted filter element210is attached to the in-tank return line formed by portion240by a threaded connection between the end cap212and the portion240, however, any other suitable compression fitting or other mechanical connection may be utilized.

In operation the hydraulic fluid is returned to the hydraulic reservoir8through the return line and into the in-tank return line formed by coupling238and first portion340. The in-tank return line, specifically the portion240, forms the housing for the filter element210, whereby the filter element210and the in-tank return line form a filter assembly. The returning hydraulic fluid will, normally, flow though the filter media220, and through the opening214into the hydraulic reservoir holding tank. This forms an outside-in filter element that uses the return line pressure for filtration, no additional work or energy is needed for the filtration process, and there is no additional drag on the system.

The bypass valve assembly224operates in a conventional manner as an emergency bypass, essentially as described above in connection with bypass valve24. The spring228is set to a by-pass pressure. If the filter media220is close to reaching its capacity, the pressure in the in-tank return line will increase until it reaches the by-pass pressure of the spring228. At the by-pass pressure the spring228will be depressed by the valve body230allowing fluid to flow through openings (not shown) in the valve housing226to the opening214. Activation of the by-pass valve assembly224by-passes the filter media220, as known in the art. The in-line, in-tank return line positioning of the filter element210allows for a simple by-pass valve alarm to be utilized. The hydraulic reservoir8holding tank is vented to atmosphere and will therefore be at atmospheric pressure. A simple pressure sensor (not shown) can be connected to the in-tank return line to measure in-tank return line pressure. An alarm or other indication can be set at, or slightly below the by-pass pressure to give warning of the by-pass activation. In other words the alarm can indicate that immediate maintenance is required. The standard maintenance will be the replacement of the filter element210.

The filter element210is designed for easy replacement and is bottom mounted relative to the in-tank return line. The replacement is through the man-way or cleanout access6in the hydraulic reservoir8. The operator will unthread the end cap212to disengage the filter assembly210. With the filter element210disengaged, the old filter element210can be removed and a new filter element210inserted. The new filter element210can be secured by threading on end cap212. The “bottom mounting” can be more precisely defined as a mounting that attaches to the in-tank return line opposite to the direction of flow and is disengaged in the direction of flow.

The filter element210can be used with a variety of existing hydraulic reservoirs8. All that is required is the presence of an in-tank return line sufficient for receiving the filter element210to form a filter assembly therein, and an access port6for inserting and replacing the filter element210. It is anticipated that the first portion240may also be retrofitted onto existing hydraulic tanks8to utilize the filter element210.

FIG. 4is a sectional view of an in-tank return line for a hydraulic reservoir8having a filter element310according to a third embodiment of the present invention. Additionally, as will become apparent, the hydraulic reservoir8will need to have a man-way opening6(such as shown inFIG. 3), or clean out access for replacement of the bottom mounted filter element310. The term “bottom mounted” within the meaning of this specification means that the filter element310will be withdrawn (i.e. replaced) in a direction of the flow of the in-tank return line and the filter element310will be attached to the return line by moving the filter element310along the direction opposite the flow in the in-tank return line. This is the opposite of the “top mounted” filter elements ofFIGS. 1-2. These terms are not intended to define a specific direction of the in-tank return line which may extend from the top, bottom or side of the hydraulic reservoir8. The details of the hydraulic reservoir8are known in the art and are not described herein in detail.

The bottom mounted, in-tank return line filter element310includes an end cap312coupled to an in-tank return line as described here and after. The end cap312includes a central opening314for receiving the hydraulic fluid through the filter element310and into the hydraulic reservoir8. The end cap312further includes an upper mounting surface316and a peripheral attachment surface318. The attachment surface318can include a groove as shown inFIG. 4, or an external bead, pair of spaced beads projected beads or other associated configuration to assist in the attachment of the filter element310to the in-tank return line.

A filter media320is bonded to the mounting surface316such as through an epoxy or other conventional attachment techniques. The filter media320includes a filtering structure and a support tube providing structural support (i.e. a backbone) to the filter media320as is known in the art.

A mounting flange322is attached to a distal end of the filter element320opposite the end cap312. The mounting flange322allows for the attachment of a bypass valve assembly324. The bypass valve assembly324includes an extended valve housing326, a spring328and a valve body330.

The end cap312, a filter media320, mounting flange322and bypass valve assembly324combined to form the bottom mounted, in-tank return line filter element310according to the present invention. The in-tank return line filter element310is positioned within an in-tank return line that extends into the hydraulic reservoir8to form a filter assembly.

InFIG. 4the in-tank return line is formed by a first return line portion340extending from the return line at the periphery of the hydraulic reservoir8. The first portion340includes an external barb342at a lower portion thereof. The in-tank return line ofFIG. 4includes a second portion formed by hydraulic hose350. The hose350is coupled to the first portion340with a hose clamp352positioned above the external barb342. Any other suitable compression fitting or other mechanical connection may be utilized in place of the hose clamp352. When extending from an upper portion of the hydraulic reservoir8, the in-tank return line may extend past the centerline of the reservoir8and preferably into a position well below the normal fluid level line within the hydraulic reservoir holding tank. This design will help avoid foaming within the fluid in the holding tank and will generally improve the fluid flow characteristics within the hydraulic reservoir8.

The bottom mounted filter element310is attached to the in-tank return line by a hose clamp354securing the hose350to the attachment surface318of the end cap312. The groove on the attachment surface318will assist in maintaining the filter element310in position. As with hose clamp352, any other suitable compression fitting or other mechanical connection may be utilized in place of the hose clamp354.

In operation the hydraulic fluid is returned to the hydraulic reservoir8through the return line and into the in-tank return line formed by first portion340and hose350. It will be apparent from a review ofFIG. 4that the in-tank return line, specifically the hose350, forms the housing for the filter element310, whereby the filter element310and the in-tank return line form a filter assembly. The returning hydraulic fluid will, normally, flow though the filter media320, and through the opening314into the hydraulic reservoir holding tank. This forms an outside-in filter element that uses the return line pressure for filtration. In other words no additional work or energy is needed for the filtration process, and there is no additional drag on the system.

The bypass valve assembly324operates in a conventional manner as an emergency bypass. The spring328is set to a by-pass pressure. If the filter media320is close to reaching its capacity (i.e. it is clogged), the pressure in the in-tank return line will increase until it reaches the by-pass pressure of the spring328. At the by-pass pressure the spring328will be depressed by the valve body330allowing fluid to flow through openings (not shown) in the valve housing326to the opening314. Activation of the by-pass valve assembly324by-passes the filter media320, as known in the art. The in-line, in-tank return line positioning of the filter element310allows for a simple by-pass valve alarm to be utilized. The hydraulic reservoir8holding tank is vented to atmosphere and will therefore be at atmospheric pressure. A simple pressure sensor (not shown) can be connected to the in-tank return line to measure in-tank return line pressure. An alarm or other indication can be set at, or slightly below the by-pass pressure to give warning of the by-pass activation. In other words the alarm can indicate that immediate maintenance is required. The standard maintenance will be the replacement of the filter element310.

The filter element310is designed for easy replacement and is bottom mounted relative to the in-tank return line. The replacement is through the man-way or cleanout access6in the hydraulic reservoir8. The operator will release the hose clamp354to disengage the filter assembly310. With the filter element310disengaged, the old filter element310can be removed and a new filter element310inserted. The new filter element310can be secured by reattaching the hose clamp354. The “bottom mounting” can be more precisely defined as a mounting that attaches to the in-tank return line opposite to the direction of flow and is disengaged in the direction of flow.

The filter element310can be used with a variety of existing hydraulic reservoirs8. All that is required is the presence of an in-tank return line sufficient for receiving the filter element310to form a filter assembly therein, and an access port6for inserting and replacing the filter element310. It is anticipated that the first portion340and hose350may also be retrofitted onto existing hydraulic tanks8to utilize the filter element310.

Various changes may be made to the filter element310as will be apparent to those in the art. For example the end cap312may be machined from metal with a sealing O-ring or may be injection molded to provide a thinner profile.

FIG. 2illustrates a forth embodiment of the present invention which incorporates some changes. The bottom mounted, in-tank return line filter element410includes an end cap420coupled to an in-tank return line440, that may be a steel tube. The end cap420includes a central opening314and an upper mounting surface316as discussed above. The end cap420includes a modified peripheral attachment surface480that includes threads456to assist in the attachment of the filter element410to the in-tank return line440. An O-ring458and sealing gasket460on a shoulder of the end cap420are also provided for sealing the filter element410.

A filter media320is bonded to the mounting surface316and a mounting flange322is attached to a distal end of the filter media320opposite the end cap312, as described above in connection with filter element310. A bypass valve assembly324, which includes an extended valve housing326, a spring328and a valve body330, is attached to the mounting flange322.

The end cap420, a filter media320, mounting flange322and bypass valve assembly324combined to form the in-tank return line filter element410according to the modified fourth embodiment of the present invention. The bottom mounted in-tank return line filter element410is positioned within an in-tank return line440that extends into the hydraulic reservoir8. InFIG. 2the in-tank return line440is formed by a single tube with threads at the end to engage with threads456of the end cap420. The line440is in place of the first return line portion340and hydraulic hose350associated with filter element310. The filter element410is threaded to the in-tank return line440by threads456of the attachment surface480of the end cap420.

In operation the hydraulic fluid is returned to the hydraulic reservoir8through the return line and into the in-tank return line440. The in-tank return line440forms the housing for the filter element410and combines therewith to form a filter assembly. The returning hydraulic fluid will, normally, flow though the filter element320, and through the opening314into the hydraulic reservoir holding tank. This forms an outside-in filter element that uses the return line pressure for filtration. In other words no additional work or energy is needed for the filtration process, and there is no additional drag on the system. The bypass valve assembly324operates in a conventional manner as an emergency bypass, as described above. As with the filter element310, a simple pressure sensor (not shown) can be connected to the in-tank return line440to measure in-tank return line pressure, whereby an alarm, or other indication, can be set at, or slightly below the by-pass pressure to give warning of the by-pass activation indicating that immediate maintenance (e.g. filter element410replacement) is required.

The bottom mounted filter element410is also designed for easy replacement. The replacement is through the man-way or cleanout access in the hydraulic reservoir. The operator will unthread the filter element410to disengage the filter element410. External flats may be provided on the attachment surface480, internal flats (i.e. an Allen head structure) may be provided on the opening314, or other rotation assisting mechanism may be added to assist in the rotation of the filter element410. The old filter element410can be removed and a new filter element410inserted. The new filter element410can be secured by threading the end cap420to the return line440. The filter element410can also be used with a variety of existing hydraulic reservoirs8. All that is required is the presence of an in-tank return line440sufficient for receiving the filter element410, and an access port6for inserting and removing the filter element410.

It is anticipated that the return line440may also be retrofitted onto hydraulic reservoirs8to utilize the filter element410. The retrofitting may simply be by a peripheral plate surrounding the in-tank return line440that is attached by bolts or the like to the hydraulic reservoir8. Appropriate sealing (e.g. gasket and or0-ring) of the plate would be required. This modification may make the replacement of the filter element410easier in that the entire in-tank return line440can be removed from the reservoir to access and replace the filter element410. The filter element410is still a “bottom mounted” structure, it is only the method of accessing the filter element410that may be different with this modification.

The other advantage of the present invention will be apparent to those in the art. The invention has been described with reference to the preferred embodiment. Obvious modifications and alterations will occur to others upon reading and understanding the proceeding detailed description. It is intended that the invention be construed as including all such modifications and alterations. The scope of the present invention is defined by the appended claims and equivalents thereto.