9 may be unused communication between the different modules 5 and with the widened portions 27 of the openings 25 of the first flange 23 is effected in a conventional manner by connecting members 49 inserted into the ends of the channels 43 and into the portions 27 also conventionally components 7 are mounted on the modules 5 it will be observed that only some of the modules 5 and of the components 7 have been shown in fig1 the component 7 at the top left in fig1 may for example be a valve the following component 7 on the right may be a pressure gauge and the bottom component 7 on the left may be a filter cleaner thus on each face 9 a circuit is formed the whole of the circuits making it possible to carry out the required measurements and analyses of the fluid it will be noted that elbowed connecting members 63 fig6 may be used in some variants to connect to one another modules 5 provided on adjacent faces 9 and therefore the circuits which they carry the body 3 is provided at its second end on the right in fig1 with a second flange 51 for holding the.