as can be observed from fig5 a , said reservoir 3 can comprise an outer wall 32 , said outer wall 32 being traversed by said outlet 20 and inlet 40 nozzles and comprising a bottom portion 320 forming a base , a lateral portion 321 forming a side wall and an upper portion 322 forming a crown , and an inner wall 33 forming , together with said filtration means 5 , a partition of said reservoir 3 which isolates said upstream 4 and downstream 2 ′ enclosures . other vertical or substantially vertical bulkheads ( not shown ) extend from its base and over some of the height of the reservoir . as can be seen from fig5 a and 5 b , said upstream enclosure 4 can form a container body 4 ′ equipped with a wall , termed an upstream wall 41 , comprising an opening 42 , typically an upper opening 42 ′, cooperating with said filtration means 5 , one portion of said upstream wall 41 forming said inner wall 33 , the other portion of said upstream wall 41 forming a wall , termed a common wall 10 , with said outer wall 32 , said common wall 10 being traversed by said inlet nozzle 40 , typically perpendicular to said common wall 10 . said common wall 10 can comprise a first common wall 10 a forming part of said lateral portion 321 of said reservoir 3 . furthermore , said common wall 10 can comprise a second common wall 10 b forming part of said bottom portion 320 of said reservoir 3 . according to another configuration , which has not been illustrated by a figure , said common wall 10 can optionally comprise a third common wall forming part of said upper portion 322 of said reservoir 3 . as illustrated in fig4 a and 4 b , said reservoir 3 can be a reservoir 3 ′ made of plastic comprising a shell , termed a lower shell 34 , and a shell , termed an upper shell 35 , said lower 34 and upper 35 shells being molded parts 34 ′, 35 ′ assembled by their assembly flanges , said lower shell 34 having a flange , termed an upper assembly flange 340 , cooperating with a flange , termed a lower assembly flange 350 , of said upper shell 35 in an assembly plane 36 so as to form said reservoir 3 . as illustrated in fig1 a and 1 b , said container body 4 ′ forming said upstream enclosure 4 can be an axial container body 4 ″ having an axial direction 43 , said body 4 ″ comprising a base 410 , a lateral skirt 411 having a typically circular cross section in a plane perpendicular to said axial direction 43 , and said opening 42 typically having said cross section . according to the invention and as illustrated in fig2 a to 3 b , said filtration means 5 can form a composite filtration element 5 ′ comprising a peripheral portion 50 assembled in a sealed manner to said container body 4 ′, 4 ″, and a filtering central portion 51 . said filtering central portion 51 can form a filter cloth 51 ′ and said peripheral portion 50 can form an annular part 50 ′ made of plastic overmolding the whole of a peripheral edge 510 of said filter cloth 51 ′ so as to secure said filter cloth 51 ′ to said annular part 50 ′, and such that all of said upstream fluid flowing from said upstream enclosure 4 toward said downstream enclosure 2 ′ passes through said filter cloth 51 ′ in order to rid said upstream fluid of said solid particles . according to one configuration illustrated in fig3 a and 3 b , said annular part 50 ′ can be a part termed a short annular part 50 a , said short annular part 50 a essentially comprising an annular sealing lip 500 . in one advantageous embodiment , said filter cloth 51 ′ has a mesh size of between 50 and 250 μm , preferably between 100 and 150 μm . by way of example , a mesh size of 120 μm is very suitable . said central filtering portion 51 can be formed of polyamide ( pa ) or polypropylene ( pp ). according to another configuration illustrated in fig2 a and 2 b , said annular part 50 ′ can be a part termed a long annular part 50 b , said long annular part 50 b comprising said sealing lip 500 and an axial projection 501 designed to slide inside said container body 4 ′, 4 ″, said axial projection 501 advantageously comprising a cut - out portion 502 facing said inlet nozzle 40 . in one particular embodiment , said sealing lip 500 can cooperate in a sealed manner with a flange 412 of said container body 4 ′, 4 ″, advantageously by means of an annular weld . as can be seen from fig1 b , 3 c and 5 b , said container body 4 ′, 4 ″ can comprise at least one inner radial projection 44 providing a predetermined axial positioning for said filtration means 5 with respect to said container body 4 ′, 4 ″. as illustrated in fig4 a to 5 a , said device 1 can comprise a means 6 for detecting the level of said downstream hydraulic fluid in said downstream enclosure 2 ′. it can be seen from these same figures that said reservoir 3 can comprise an upper opening 37 closed by a removable cap 38 so as to allow a filling , for example an initial filling , of said downstream enclosure 2 ′ with hydraulic brake fluid . as illustrated in fig5 a , said assembly plane 36 can be a horizontal plane 36 ′, said horizontal assembly plane 36 ′, being intended to be located preferably above the level of said downstream hydraulic fluid in said downstream enclosure 2 ′. according to the invention , said filtration means 5 can have a filtering area ranging from 0 . 15 cm 2 to 100 cm 2 , preferably from 2 cm 2 to 20 cm 2 , and preferably still from 3 cm 2 to 10 cm 2 . this large filtering area has an advantage over an installation of the filtration means in a hydraulic line , since hydraulic lines generally have quite a small diameter of around 4 or 5 mm . owing to the large filtering area , the filtration means is not at risk of being obstructed by the particles and debris which it retains . moreover , given the installation of the filtration means 5 in the supply reservoir 3 and given its geometric arrangement , most of the retained particles and debris drop to the bottom of the upstream portion 31 of said reservoir 3 , where they are not at risk of being entrained into the outlet nozzles 20 . however , it would not constitute a departure from the scope of the present invention to design the filtration means to extend vertically and / or obliquely . according to the findings observed by the applicant , the device according to the invention makes it possible to use the same filter cloth throughout the life of the device in the knowledge that , given the method , namely welding , used to assembly the two shells which form said device , it is virtually impossible to replace said filter cloth . typically , said downstream enclosure 2 ′ and said upstream enclosure 4 can have storage capacities respectively designated c v and c m such that the ratio c v / c m ranges from 3 to 30 . the figures correspond to exemplary embodiments of devices 1 or parts of devices 1 according to the invention . two configurations of the device 1 , which is represented particularly in fig4 a and 4 b , were manufactured : a ) according to a first configuration , the filtration means 5 comprises an annular part with a short skirt 50 a as represented in fig3 a and 3 b , b ) according to a second configuration , the filtration means 5 comprises an annular part with a long skirt 50 b as represented in fig2 a and 2 b . for that purpose : upper shells 35 , 35 ′ were manufactured or made available by molding a plastic , for example a polypropylene ; a first configuration 34 a of lower shell 34 , 34 ′ tailored to said annular part 50 a with a short skirt was manufactured , as illustrated in fig5 a and 5 b ; a second configuration 34 b of lower shell 34 , 34 ′ tailored to said annular part 50 b with a long skirt was manufactured , as illustrated in fig1 a and 1 b , the lower shells 34 , 34 ′, 34 a , 34 b being formed by molding a thermoplastic , for example a polypropylene . in this case , as can be seen from fig1 a , 1 b and 3 c , said upstream enclosure 4 , 4 ′, 4 ″ comprises a plurality of radial projections 44 and 44 ′ intended to cooperate with the axial projection 501 of the long annular part 50 b ; the detection means 6 was formed or made available and it was assembled to said upper shell 35 , 35 ′; two configurations of said filtration means 5 , 5 ′ were formed or made available , a first configuration 50 a according to fig3 a and 3 b and a second configuration 50 b according to fig2 a and 2 b . filtration means 50 a , 50 b were manufactured for example by overmolding the edge 510 of a circular portion of filter cloth 51 ′ into said annular plastic part 50 ′ forming said peripheral portion 50 ; the filtration means 50 a , 50 b was assembled in a sealed manner to the corresponding lower shell 34 a , 34 b , for example by welding the annular sealing lip 500 to the opening 42 of said upstream enclosure 4 and , for example , to the flange 412 of the lateral skirt 411 forming said upstream wall 41 ; finally , the edges 340 , 350 of the shells 34 , 35 were welded to one another so as to form said plastic reservoirs 3 , 3 ′. upper shells 35 , 35 ′ and lower shells 34 , 34 ′, 34 a , 34 b made of polyamide were also manufactured . advantageously , filter cloths 51 consisting of pp were used in the case of shells made of pp and cloths made of pa were used in the case of shells made of pa , so as to make it easier to weld the filter cloth 51 to the lower shell 34 , 34 ′, 34 a , 34 b .