Filter

Abstract: A filter element for liquids has an outer casing (10) within which is located a central tube (13). A filter medium (14) is located between the casing and the tube. Liquid enters the medium through apertures in an upper end plate (11) and the filtered liquid leaves the medium by way of apertures in a lower end plate (12). Mounted in the lower portion of the central tube (13) is a further tube (17) through which the filtered liquid can flow into the upper portion of the central tube. The upper end of the further tube (17) is joined by a wall (18) to the central tube and air which passes through the filter medium collects in a dead space (20) defined between the tubes. An air bleed orifice (19) formed in the wall (18) allows the air to pass at a controlled rate into the filtered fuel flowing in the central tube.

Description: The present invention relates to filters for liquids the filters being of the kind which are inserted between a reservoir and an induction pump. A liquid flow takes place through the filter upon induction by the pump, the pressure between the pump and the filter being less than the pressure between the reservoir and the filter. The filtering element which forms the essential component of the filter, is constituted by a filtering medium usually paper, which operates to prevent particles which may be in suspension in the liquid in the reservoir, from damaging the induction pump. Gases and air from the reservoir circulate with the liquid in variable proportions and appear in the form of bubbles or as an emulsion. The intrinsic characteristics of the filtering medium, amongst others the size of its pores, the nature of the liquid, its viscosity, and its flow rate, are some parameters which affect the loss of pressure head in the region of the filter medium. The air or the gases are liable to be stopped by the filtering medium, whether the liquid is flowing or whether it is stopped and air pockets are formed which finally pass through the filtering medium following variations in the induction pressure of the pump. The sudden flow of air towards the pump may create difficulties in the pump during starting or in the use of the pump. Different means exist to ensure permanent degassing of the liquid flowing through the filter. Certain of these means provide for housing the filtering element in a casing of the filter assembly and for mounting on the liquid outlet tube a porous sleeve having a smaller pressure loss than that of the filtering medium of the filter element. The air is progressively evacuated by this sleeve, thus ensuring permanent degassing. However, these means partially bypass non-filtered liquid towards the filtered liquid, i.e. the filtrate. In other means, having a structure similar to that of the aforesaid means, a small orifice, protected by another filtering medium, in the filter assembly casing and connected to the outlet pipe, progressively evacuates the gases and ensures permanent degassing. These two cited means partially by-pass non-filtered liquid towards the filtrate without passing through the filtering medium. Another means known from French Patent Application No. 2677267, ensures permanent degassing through orifices situated in zones of the filtering medium. Another arrangement is seen in FR-A-1385489 in which air is allowed to collect in a portion of the unit which contains unfiltered liquid and is then allowed to escape through a float controlled valve into the filtered liquid. The invention aims to ensure permanent degassing without any means connected to the filtering element, such as sleeves or protected orifices, i.e. in as simple a manner as possible. According to the invention a filter element for liquids comprises a first tube about which is located a filter medium through which the liquid to be filtered passes, and an air bleed orifice through which air can escape, said first tube being imperforate and by a second tube which is located with clearance within the first tube so as to form therewith a dead space in which air which has passed through the filter medium can collect, said second tube receiving the filtered liquid from the filter medium, said air bleed orifice communicating with said dead space so as to allow air to flow directly into the filtered liquid at a controlled rate. The filtering medium may be made from one or a plurality of strips, for example of paper, wound together, and secured together at their upper and lower adjacent edges so that in section, the medium is of zig-zag configuration. The orifices ensure permanent degassing of the liquid which passes through the filtering medium without non-filtered liquid passing into the filtered liquid. In one embodiment the second tube opens into the interior of the first tube, the dead space being constituted by the space between the two tubes and the degassing orifices being formed in a wall connecting the two tubes. In another embodiment the second tube extends beyond the ends of the first tube, the dead space being defined by the annular space between the internal wall of the first tube and the external wall of the second tube. The invention will be better understood from the accompanying drawings in which are shown different embodiments of the filtering medium elements. In the accompanying drawings:- Figure 1 is a sectional side elevation of one example of a filter element in accordance with the invention, and Figure 2 shows a modification of the element shown in Figure 1. With reference to Figure 1, the element comprises an outer casing 10 of hollow cylindrical form having at its opposite ends end plates 11, 12. One of the end plates may be formed integrally with the casing and the other end plate secured to the casing by edge rolling once the filter medium as will be described, is located in position. Each end plate is provided with a central aperture between which extends a first tube 13. The upper end plate 11 is provided with a series of inlet holes (not shown), through which liquid can enter the element and the lower end plate 12 is provided with a series of outlet holes or slots (not shown), through which liquid can leave the element. Located in the annular space defined between the first tube 13 and the inner surface of the casing is a filter medium 14 and in the example shown in Figure 1 this comprises at least two lengths of filter paper which are wound about the tube 13. At their upper and lower edges the lengths of paper are secured together by adhesive so as to form a filtering medium which in section is of zig-zag configuration. The medium thus formed has inlet pockets 15 which are open to the inlet holes formed in the plate 11 and outlet pockets 16 which are open to the outlet holes or slots formed in the end plate 12. The inner and outer turns of the medium are secured to the tube and the casing in a liquid tight manner by means of adhesive. In the use of the element it is clamped between upper and lower housing parts not shown, which are secured together by means of a bolt which extends through the tube 13 so as to form a filter unit. The upper housing part defines a rim which seals against the upper edge of the casing 10 and a depending spigot which locates in sealing engagement with the internal surface of the tube 13. The housing part defines a liquid inlet connection which opens into a space above the upper end plate 11 and it also defines a liquid outlet connection which extends through the spigot and communicates with the interior of the tube 13. The lower housing part defines a rim which seals against the lower edge of the casing 10 and it defines a space or trough whereby liquid leaving the outlet holes in the end plate 12 can flow into the lower end of the tube 13 and into a second tube to be described. As shown in Figure 1 there is located within the lower portion of the first tube 13, a second tube 17 which is of smaller diameter and which projects downwardly below the lower end of the tube 13. An annular partition wall 18 extends between the upper end of the tube 17 and the internal surface of the tube 13 and formed in the wall is a small air bleed orifice 19. In use, the filter unit is interposed between a fuel reservoir and a fuel pump of a fuel system of an internal combustion engine. The fuel will contain entrained air and solid contaminant. The solid contaminant will be retained in the inlet pockets 15 and the air will tend to collect in the inlet pockets but will eventually pass through the filter paper into the outlet pockets and will be carried by the fuel flow through the outlet holes or slots in the lower plate 12. The air will tend to flow upwardly into the annular dead space 20 defined between the tubes 17 and 13 whereas the fuel will flow through the tube 17 into the tube 13. The air in the dead space 20 is allowed to leave the space in a controlled manner through the small orifice 19 as a steady stream of small bubbles whereas the air will tend to flow into the space as large bubbles which if they were allowed to flow to the pump, could upset the operation of the pump. The stream of small bubbles will not upset the operation of the pump. In the arrangement shown in Figure 2 the apertured upper end pate 11A extends inwardly about the second tube 17A so that the dead space 20A extends the full height of the element. The upper end of the tube 17A extends beyond the upper end of the plate 11A and in use communicates with the liquid outlet connection in the upper housing part. Moreover, the air heed orifice or orifices 19A are formed in the wall of the tube 17A. Whilst it is envisaged that the tube 17A is part of the filter element it may be integral with the upper housing part. In this case the upper end plate 11A would be provided with an opening to allow the tube 17A to pass through. Liquid flows from the filter medium through apertures in the lower end plate 12A.

Claims: A filter element for liquids comprising a first tube (13) about which is located a filter medium (14) through which the liquid to be filtered passes, and an air bleed orifice (19, 19A) through which air can escape, characterised in that said first tube (13) is imperforate and by a second tube (17, 17A) which is located with clearance within the first tube so as to form therewith a dead space (20, 20A) in which air which has passed through the filter medium can collect, said second tube (17, 17A) receiving the filtered liquid from the filter medium, said air bleed orifice (19, 19A) communicating with said dead space (20, 20A) so as to allow air to flow directly into the filtered liquid at a controlled rate. A filter element according to Claim 1, characterised in that the second tube (17) extends downwardly below the first tube (13) and the orifice (19) is formed in a wall (18) which interconnects the upper end of the second tube (17) with the internal surface of the first tube (13) at a position intermediate the ends of the first tube. A filter element according to Claim 1, characterised in that the second tube (17A) extends beyond the opposite ends of the first tube (13), the dead space (20A) defined between the tubes being closed at the upper end of the first tube and the orifice (19A) being formed in the wall of the second tube intermediate the ends of the first tube.

Inventors: BRUN PHILIPPE, BRUN, PHILIPPE
Applicants: LUCAS IND PLC, LUCAS INDUSTRIES PUBLIC LIMITED COMPANY
Application year: 1993
Main classification: B01D35
IPC codes: B01D35, B01D29, B01D36