Fuel filter, in particular for diesel fuel

Abstract: The filter comprises a first chamber (31) communicating with the fuel inlet; a second chamber (32), downstream of the first chamber (31), into which the filtered fuel enters and which communicates with the outlet (12); a filter medium (20) for filtering off the impurities, which separates the second chamber (32) from the first chamber (31); and a third chamber (33) in which that fuel portion repelled by the filter medium (20) collects. There is also provided a mesh surface (40) separating the second chamber (32) from the first chamber (31) and coated with a substance such as poly-tetra-fluoro-ethylene (PTFE) or silicone or the like, it having passage pores of diameter not greater than about 200 microns to intercept the water parts present in the fuel.

Description: This invention relates to the filtration of fuel, in particular fuel (generally known as gasoil) for diesel engines. In this sector the sophistication of injection equipment requires the most careful filtration to prevent the impurities present in the fuel causing damage to and malfunction of the delicate injection equipment. A technical problem which has not been totally solved is caused by the presence of water parts in the fuel, which are not intercepted by the usual filter cartridges (designed to intercept more solid parts) and hence reach the downstream mechanical members, resulting in oxidation problems and breakage thereof. For this problem, upstream of the cartridge there is inserted an inclined surface generally of frusto-conical shape, along which the entering fuel flow runs before reaching the filter cartridge. Because the water has a greater specific gravity than the fuel, it tends to move more towards the inclined surface, where its travel is decelerated, with the result that the water particles tend to unite to form relatively large water droplets, which then fall to the base of the filter, where they collect without passing through the filter cartridge. A fuel fitter having the above mentioned features is shown in EP-A-0412210. In GB-A-2138693, a fuel filter is shown which, in order to separate the water, has a separator member, comprising hydrophobic screen elements, which prevents water droplets from passing there through but it is permeable to fuel These solutions are not however totally satisfactory, in that generally at least a fraction of the water is not separated and reaches the outlet to cause the described problems. An object of the present invention is therefore to provide a filter able to more effectively separate the water present in fuel, in particular in diesel fuel, and possibly to achieve complete separation. This and further objects are attained by the present invention as characterised in the claims. The invention is based on the idea of adding to the usual filter cartridge within a filter of known type a mesh surface through which the entire fuel flow passes. This mesh surface is coated with a substance such as poly-tetra-fluoro-ethylene (PTFE) or silicone or similar equivalent substances, and has passage pores of diameter not greater than about 200 microns, it having proved able to prevent passage of the water parts present in the fuel. Said mesh surface is positioned preferably (but not necessarily) downstream of an inclined surface for water pre-separation. The invention is described in detail hereinafter with the aid of the accompanying figures, which illustrate a non-exclusive embodiment thereof. Figure 1 is a vertical elevation of the filter shown partly sectioned on an axial plane. Figure 2 is a section on the plane I-I of Figure 1. Figure 3 is a section on the plane II-II of Figure 1. The filter comprises an outer container 10 of vertical axis A, in particular being of substantially cylindrical shape with slight lower end dishing. The fuel inlet and outlet are located on the upper cover 14 of the container 10. Specifically, the inlet is defined by various apertures 11 regularly distributed along a circumference with its centre on the axis A, the outlet being a single aperture with its centre on the axis A. Within the container 10 there is a filter cartridge 20 of known type, the cross-section of which is in the form of a circular crown, substantially coaxial with the container 10. The cartridge 20 defines the filter medium for filtering off the impurities present in the fuel. The outer diameter and height of the cartridge 20 are rather less than the corresponding dimensions of the container 10. Consequently the outer cylindrical surface of the cartridge 20 is spaced from the inner surface of the outer container 10, and its lower surface is spaced from the base 13 of the container 10. The region external to the cartridge, above and about its lateral surface, defines a first chamber 31 communicating with the fuel inlet ports 11. The region internal to the cartridge 20 defines a second chamber 32, which is separated from the chamber 31 by the cartridge itself. The region below the cartridge 20 defines a third chamber 33 which communicates with the first chamber 31. The upper end of the cartridge 20 and its lower end are closed respectively by an upper disc 21 and a lower disc 22 which are joined to the respective ends. To the inner lateral surface of the cartridge 20 there is fixed a perforated support tube 26, the ends of which are fixed to the upper disc 21 and lower disc 22 respectively. Between the upper disc 21 and the cover 14 there is positioned a conduit 24, which is joined to these latter and connects the inner chamber 32 to the outlet aperture 12. A spring 16 is interposed between the base 13 and the lower disc 22 to maintain the cartridge (with relative discs 21 and 22) urged against the conduit 24 and this latter urged against the cover 14. Passage between the first chamber 31 and the second chamber 32 takes place only via the lateral surface of the cartridge 20, in a substantially radial direction. The lower disc 22 has apertures 22a in its periphery to provide free passage between the first chamber 31 and the third chamber 33. The chamber 31 is divided into an upper portion 31a positioned above the cartridge 20, and a lower portion 31b freely communicating with the portion 31a and positioned about the lateral surface of the cartridge 20. The upper portion 31a directly communicates with the inlet apertures 11. Within it there is provided a frusto-conical element 25 fixed to the conduit 24 and extending below the apertures 11, it being inclined outwards and downwards. Said element 25 defines an inclined surface along which the flow descends before passing through the cartridge 20, and serves to provide initial separation of the water part of the fuel. According to the invention, there is provided a mesh surface 40 which separates the first chamber 31 from the second chamber 32 and is coated with a substance such as poly-tetra-fluoro-ethylene (PTFE - usually known as teflon R ) or silicone or the like and has passage pores of diameter not exceeding about 200 microns, able to intercept the water parts present in the fuel, and is positioned against and covering the lateral surface of the cartridge 20. According to a preferred embodiment, said mesh surface 40 is positioned coaxial to the cartridge 20, and is arranged to intercept the entire flow which in passing from the first chamber 31 to the second chamber 32 traverses the cartridge 20. According to a preferred embodiment, the mesh surface 40 is formed from single-thread fabric, the thread diameter of which varies from 0.02 to 0.2 mm. Preferably, the mesh surface is of stainless steel, or nylon, or polyamide. Preferably the coating thickness is 2-8 microns. In practice the PTFE is applied to both sides of the surface 40, or to one side only, by spraying followed by baking in an oven. Alternatively silicone is applied to one or both sides of the surface 40. In operation, the fuel firstly enters the upper portion 31a of the first chamber 31 via the aperture 11, and then runs along the surface of the frusto-conical element 25 to pass into the lower portion 31b. The element 25 (as is known) decelerates the travel of the water particles and tends to aggregate them into relatively large droplets which then tend to fall directly into the third chamber 33, the purpose of which is to collect the parts separated from the fuel. Those water parts which are not separated by the inclined surface are in any event halted by the mesh surface 40 according to the invention. In this respect it has been experimentally found that the surface 40, having the aforesaid technical characteristics, substantially completely prevents or at least strongly limits water passage through it, whereas it provides no obstacle to the passage of the actual fuel. Presumably this favourable phenomenon is caused by a different surface tension of the water particles which, in the presence of the teflon or silicon-coated mesh 40, break the bonds with the fuel molecules, then mutually agglomerate and are unable to pass through the mesh; and hence fall downwards into the collection chamber 33, from which they are periodically extracted. Evidently the smaller the pore diameter of the surface 40, the greater is the interception action on the water particles. In practice, at around a diameter of 20 microns there is total interception of the water particles. Numerous modifications can be made to that part of the filter excluding the mesh surface 40.

Claims: A fuel filter, in particular for diesel fuel, comprising: an outer container having an inlet and an outlet; a first chamber (31) inside the outer container communicating with the fuel inlet; a second chamber (32), inside the outer container downstream of the first chamber (31), into which the filtered fuel enters and which communicates with the outlet (12); a filter medium (20) combined with a mesh surface (40), for filtering off fuel impurities, which separate the second chamber (32) from the first chamber (31), and a third chamber (33) in which that fuel portion repelled by the filter medium (20) collects; characterised in that said mesh surface (40) is coated with poly-tetra-fluoro-ethylene (PTFE) or silicone or equivalent substances, it having passage pores of diameter not greater than about 200 microns, to intercept water parts present in the fuel, and is positioned against and covering the lateral surface of the filter medium (20). A fuel filter as claimed in claim 1, characterised in that the mesh surface (40) is formed from single-thread fabric the thread diameter of which varies from 0.02 to 0.2 mm. A fuel filter as claimed in claim 1, characterised in that the mesh surface (40) is of stainless steel. A fuel filter as claimed in claim 1, characterised in that the mesh surface (40) is of nylon. A fuel filter as claimed in claim 1, characterised in that the mesh surface is pf polyamide. A fuel filter as claimed in claim 1, characterised in that the coating thickness is 2-8 microns. A fuel filter as claimed in claim 1, characterised by comprising: an outer container (10) of vertical axis and having an inlet (11) and an outlet (12), a filter cartridge (20) of cross-section in the form of a circular crown, substantially coaxial to the outer container (10) and having its outer cylindrical surface spaced from the inner surface of the outer container (10) and its lower surface spaced from the base (13) of the outer container (10), a conduit (24) for communication between the region (32) within the filter cartridge (20) and the outlet (12), means (21, 22, 24) for closing the lower end of the cartridge (20) and its upper end, so that the only passageway between the region (31) external to the cartridge and the inner chamber (32) is via the lateral surface of the cartridge (20), said first chamber (31) being defined by the region above and surrounding the cartridge (20), said second chamber (32) being defined by the region within said cartridge (20) and said third chamber (33) being defined by the region below the cartridge (20), said mesh surface (40) being positioned coaxial to the cartridge (20) and being arranged to intercept the entire flow which traverses the lateral surface of the cartridge (20). A fuel filter as claimed in claim 7, characterised in that above the lateral surface of the cartridge (20) there is located an inclined surface (25) along which the flow descends before passing through the cartridge (20), said surface (25) achieving an initial separation of the water part of the fuel.

Inventors: GIRONDI GIORGIO, GIRONDI, GIORGIO
Applicants: UFI FILTERS SPA, UFI FILTERS S.P.A.
Application year: 1997
Main classification: B01D36
IPC codes: B01D27, B01D39, F02M37, B01D17, B01D35, B01D36