WO1999022841A1

WO1999022841A1 - Disposable filter element

Info

Publication number: WO1999022841A1
Application number: PCT/US1998/023374
Authority: WO
Inventors: Lang Luo; Michael Schmitt; Abbas F. Vijlee
Original assignee: Alco Industries, Inc. Doing Business As Schroeder Industries
Priority date: 1997-11-04
Filing date: 1998-11-03
Publication date: 1999-05-14
Also published as: GB0012027D0; DE19882784T1; TW391887B; GB2347361B; AU1376799A; GB2347361A; DE19882784B4

Abstract

A fluid filter element (10) for a permanent perforated core hydraulic fluid filter system is disclosed herein. The filter element (10) includes a rigid resin mesh tube (16) having a thickness of at least 0.050 inch with an inner diameter enabling a sliding fit over the permanent core, filter media (12) in a tubular shape abutting the rigid resin mesh tubing (16), end caps (18, 20) secured to the axial ends of the rigid resin mesh tube and the media, and seals (24) for sealing the end caps to the permanent perforated core.

Description

DISPOSABLE FILTER ELEMENT BACKGROUND OF THE INVENTION An essential part of any hydraulic system is a filtering system to maintain the hydraulic fluid free of particles that would wear the surfaces of pistons and cylinders, hydraulic motors and valves. Substantially all hydraulic systems have a filter that cleans the hydraulic fluid before it returns to the reservoir.

Most hydraulic filters comprise a housing that can withstand the pressures in the hydraulic system with a filter element of the pleated media type inserted within the housing. Filter elements must be designed to resist collapse under the pressure drop that develops across them as the filter media becomes contaminated. Since most hydraulic filter elements are tubular with flow of fluid passing radially inward to a central outlet passage, they are provided with a perforated tubular steel core to support the media from collapse. The filter elements have typically been supplied as a canister with the pleated filter media positioned around the tubular steel center tube. Once the media has become contaminated beyond use, the entire canister is replaced in the housing.

Another type of filter system has a permanent perforated tubular core so that the filter element may be "coreless". See, for example, U.S. Patents Nos . 4,218,324 and 5,476,585. The advantage of this system is that the filter element can be easily disposed of by crushing or burning .

Unfortunately, it has been found that when existing coreless filter elements are spent, it is difficult to slide them off of the permanent core. Often times it is necessary to use tools to pry the spent tubular cartridge in the axial direction off of the permanent core. At times the design of the housing is such that there is no physical space to let tools be used. The difficulty in removing the coreless elements seems to be directly related to the pressure developed across the filter media during the filtering process. It is an object, according to this invention, to provide a filter cartridge for use with a permanent core filter system that is easily removed from the core when the filter media becomes contaminated. SUMMARY OF THE INVENTION

Briefly according to this invention there is provided a filter element for use with a permanent perforated core . The filter element comprises a rigid resin mesh tube having a thickness of at least 0.050 inch with an inner diameter enabling a sliding fit over the permanent core, a pleated filter media folded in a tubular shape abutting the rigid resin mesh tubing, an exterior mesh wrapped about the pleated filter media, end caps secured to the axial ends of the rigid resin mesh tube and the pleated media, and means for sealing the end caps to the permanent perforated core.

BRIEF DESCRIPTION OF THE DRAWINGS Further features and other objects and advantages will become clear from the following drawings in which: Fig. 1 is a section view of a filter element according to this invention;

Fig. 2 is an end view of a filter element according to this invention; and

Fig. 3 is a graph illustrating the forces needed to remove prior art filter elements and filter elements according to this invention from permanent perforated cores .

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The prior art coreless filter elements are difficult to pull off the permanent perforated core. It is apparent that as the pressure drops across the filter media increases, the filter media is forced into the perforations in the permanent core. The difficulty in removing the prior art filter cartridges is directly related to the amount of pressure drop developed across the filter media. Referring now to Figs. 1 and 2, a filter element

10 is provided with a rigid mesh tube 16 that has a thickness of .063 inch and an open area of about 36 percent. The tube is made of polypropylene as the primary resin. Other resins may be included, for example, PE, HDPE, LDPE, LLDPE and EVA. The tube may be easily crushed when compacted across a diameter and would have insufficient strength to support the filter media m the absence of the permanent perforated core. Preferably, the tube has a plurality of circumferential strands that lie in a plane that is perpendicular to the axis of the tube. It has sufficient strength and resilience in the circumferential direction, however, enabling it when supported by the permanent core to resist circumferential strain and perhaps even to return to its original circumferential dimension after the pressure drop across the filter element has been removed . The remaining portions of the filter element are common. The pleated filter media 12 may be paper or glass fiber sheets sandwiched between flexible plastic mesh. The exterior of the filter element is wrapped with a flexible plastic net 14 which may be secured by a hot melt plastic bead laid over the exterior surface of the filter element in a helical pattern. At each end of the filter element is an end piece 18, 20. Attached to one end piece is a handle 22. One end piece has an annular groove on the inside diameter for receiving an 0-rιng 24 that enables sealing to the permanent core.

A test was conducted to compare filter elements according to this invention with filter elements according to the prior art. The test was conducted by placing a filter element on a permanent perforated core, passing hydraulic fluid through the element at a given pressure drop, and then measuring the force required to remove the filter element once the flow was stopped through the element . Two filter elements according to the prior art and two filter elements according to this invention were tested with pressure drops ranging up to 30 psid. The results are presented graphically on Fig. 3. As can be seen with the prior art filters, the greater the terminal pressure drop across the filter element the more force that is required to remove the filter element from the permanent core. On the other hand, the increase in terminal pressure drop across the filter element according to this invention does not increase the force required to remove the filter element.

Having thus described our invention in the detail and particularity required by the Patent Laws, what is desired protected by Letters Patent is set forth in the following claims.

Claims

WHAT IS CLAIMED IS:

1. A filter element for a permanent perforated core hydraulic fluid filter system comprising: a rigid resin mesh tube with an inner diameter enabling a sliding fit over the permanent core, said resin mesh tube having insufficient strength to resist collapse of the filter element under the pressure drop that develops across the filter element in use but sufficient thickness to permit easy removal of the filter element after use; filter media in a tubular shape abutting the rigid resin mesh tubing; end caps secured to the axial ends of the rigid resin mesh tube and the media; and means for sealing the end caps to the permanent perforated core.

2. A filter element for a permanent perforated core hydraulic fluid filter system comprising: a rigid polypropylene mesh tube having an axis and having a thickness of at least 0.050 inch with an inner diameter enabling a sliding fit over the permanent core, said tube having an open space of at least 36 percent based on the total area of the tube surface and a plurality of circumferential strands lying in a plane that is substantially perpendicular to the axis of the tube; a pleated filter media folded in a tubular shape abutting the rigid resin mesh tubing; an exterior mesh wrapped about the pleated filter media; end caps secured to the axial ends of the rigid resin mesh tube and the pleated media; and means for sealing the end caps to the permanent perforated core.