GB2255514A - Filter element - Google Patents

Abstract

A filter element 12 comprises two strips of filter paper wound spirally round an impervious centre tube 13 and secured together by adhesive along their edges to present a zig-zag radial section designed for axial flow. To minimise manufacturing problems and ensure good adhesive seals, the ratio between outer and inner diameters of the element is between 1.15:1 and 1.3:1. As shown, the perforate end plate 15 of the element is clamped between two parts 17, 21 of a fuel filter housing. Fuel flows from inlet 26 to outlet 27, and the interior space of the element provides room for water and possibly fine solids to settle and may accommodate a hand priming pump and a heater. <IMAGE>

Description

FILTER ELEMENT.

This invention relates to a paper filter element of the kind comprising a centre tube about which is wound at least two strips of filter paper, the longitudinal edges of the strips of paper being secured together by means of adhesive so that the filter element is of zig zag form in radial section.

The paper is wound upon the centre tube and adhesive is applied as winding takes place. As the amount of paper which is wound upon the tube increases the torque required to rotate the tube increases in proportion to the radius of the wound portion of the element providing the tension applied to the strips of paper remains constant. The torque is transmitted through the wound portion of the element and as the torque increases there is a tendency for further tightening of the wound turns particularly those which are adjacent the tube to take place. Such variation in tightening can cause damage to the adhesive bond with the result that the strength of the bond is impaired. If the strength of the bond is impaired there is a risk that the paper element will burst or at least leak in use to allow the liquid being filtered to flow through the filter element without filtering taking place.

The object of the invention is to provide a filter element of the kind specified in an improved form.

According to the invention in a filter element of the kind specified the ratio between the inner and outer diameters of the element should lie within the range 1.3:1 to 1.15:1.

In the accompanying drawings: Figure 1 shows in sectional side elevation one example of a filter element in accordance with the invention, and Figure 2 shows the element of Figure 1 mounted in a casing to form a filter unit.

Referring to Figure 1, the paper filter element is generally indicated at 12 and comprises a centre tube 13 about which is wound in spiral fashion, two lengths of filter paper. One length of paper may be coated on one side adjacent one longitudinal edge and on the other side adjacent the other longitudinal edge so that during the winding operation adjacent turns of the paper will be secured together by the adhesive so that a section through the filer element will show the two lengths of paper and in particular the turns produced thereby to be secured together in zig zag formation.

The outer turns of the filter element are secured by adhesive to the internal surface of a thin outer tube 14. However, the outer tube may be a few turns of the paper which are secured together to form the equivalent of the outer tube.

At one end of the wound element there is provided an annular perforated end closure 15 which extends outwardly beyond the outer tube 14 and which is provided with an annular lip 16 which extends about the outer tube for the purpose of providing an integral seal.

Referring now to Figure 2 the element as described is shown located in two part casing to form a filter unit which is intended to filter fuel flowing to an internal combustion engine. The illustrated casing which is one example only, comprises a lower casing part 17 of hollow stepped cylindrical form having its lower end closed by a base wall in which is formed an opening 18. At its upper end the casing part 17 defines a flange 19 which abuts against a flange 20 of an upper casing part 21. The two casing parts may be secured together by means of a bolt which extends through the opening 18 and is engaged within the threaded end of a tube 22 which depends from the upper casing part 22.

The upper casing part has an inner annular wall 23 which extends downwardly below the level of the flange 20 and on its outer side the wall provides location for an annular seal member 24. As will be seen from Figure 2 the element 12 is located within the lower casing part 17 with its lower end supported at the junction between the wider and narrower portions of the lower casing.

The end closure 15 is accommodated within stepped recesses formed in the flanges 19 and 20 to form a fuel tight seal when the casing parts are secured together.

Moreover, the seal member 24 establishes a fuel tight seal with the centre tube 13.

An annular space 25 is defined by the end closure 15 and the adjacent portions of the upper casing part 21 and in the example the space is connected to a fuel inlet 26. A fuel outlet 27 is provided which communicates with the interior of the tube 22. In use, as the fuel flows through the filter element dirt will be retained in the element and the water in the fuel will tend to form large droplets which will collect in the lower portion of the casing. It will be seen that the tube 22 extends only part way down the element so that there is an increased distance for the fuel to flow as compared with existing designs, from the lower end of the filter element to the entrance to the tube thereby ensuring that good separation of the fuel and water takes place.It will also be noted that the step adjacent the lower end of the element inclines downwardly and this facilitates the separation of fuel and water. Spaced about the step and upstanding therefrom there may be provided support plates to provide support for the element.

In order to ensure that the filter element can cope with the high fuel pressures which prevail even in the low pressure fuel system of a fuel injection system of an engine, the ratio of the inner diameter of the filter element to the external diameter should lie within the range 1.3:1 to 1.15:1. In the construction of filter elements which lie within the above range, the torque variation which occurs as the element is wound about the centre tube, is kept to an acceptable minimum so as not to cause damage to the adhesive bond as the element is wound. Moreover, the initial turns of the element that is to say those adjacent the centre tube contribute to the effective filter area of the element to a greater extent than the initial turns of the known elements because of the increased diameter of the element.

The resultant element has a larger diameter than known elements so that more space is required to accommodate the fuel filter adjacent the engine installation. However, the proposed form of filter does have a higher filtering efficiency and furthermore, the increased internal diameter permits the incorporation into the filter unit of a fuel treatment device such as a fuel heater. The heater or such other treatment device would be secured to the upper casing part. Moreover there is sufficient space in the filter unit to provide sedimentation zones in which the very fine particles of dirt separate from the fuel after it has passed through the element. The unit is also of sufficient size to accommodate a hand priming pump.

Claims (3)

1. A paper filter element comprising a centre tube about which is wound two strips of filter paper, the longitudinal edges of the strips of paper being secured together by means of adhesive so that the filter element is of zig-zag form in section and the ratio between the inner and outer diameters of the element lying within the range 1.3:1 and 1.15:1.

2. A filter unit comprising an upper casing part and a lower casing part, said parts defining peripheral flanges respectively between which is trapped part of an end closure of an annular filter element, the filter element having a centre tube which is in sealing engagement with an inner annular wall depending from the upper casing part, there being wound about the centre tube two strips of filter paper the longitudinal edges of which are secured together by means of adhesive so that the wound strips of paper have a zig-zag form in section, the ratio between the inner and outer diameters of the element lying within the range 1.3:1 and 1.15:1.

3. A filter element substantially as hereinbefore described with reference to the accompanying drawings.