the cleaning arrangement which is illustrated in fig1 - 6 comprises a cleaning nozzle 1 , which is fixedly arranged in the end of a flexible hose 2 for feeding compressed air to the nozzle . the hose 2 is fastened on the cleaning nozzle 1 by means of a hose clamp 3 . the parts are shown disassembled in fig2 . in fig1 the cleaning arrangement is shown inserted in a pipe - shaped duct where dust and deposits are to be removed from walls of the duct . the cleaning nozzle 1 includes a rear piece 3 and a front piece 4 dismantleable from this . the rear piece 3 is provided with a coupling pipe 3 . 1 to which the hose is secured by means of a hose clamp 5 . the coupling pipe 3 . 1 can constitute an integrated portion of the rear piece 3 , such as is shown for example in fig2 and 4 , or it can be secured with a suitable pin 3 . 2 such as is shown in fig3 . the rear piece 3 exhibits four distribution holes 3 . 3 which are arranged symmetrically about its central axis , something which for one thing is evident from fig6 and the holes 3 . 3 are connected to the coupling pipe 3 . 1 and discharge into the forward end of the rear piece directed towards the front piece 4 . the front piece 4 , which largely has the shape of a hemisphere , shows a mixing chamber 4 . 1 which extends symmetrically about its central axis and which has the same radius which the distribution holes 3 . 3 are arranged with around the axis . the function of the mixing chamber 4 . 1 will be described further below . the rear piece 3 furthermore presents an external conical surface 3 . 4 , which extends along its periphery at its front end , and which corresponds to an internal conical surface 4 . 2 on the front piece , the assembled cleaning nozzle 1 exhibiting an annular gap 6 along the periphery of the nozzle which is directed back out towards the coupling piece 3 . 1 . the width of the annular gap 6 can be regulated by means of a washer 7 the thickness of which determines the width of the gap so that a thicker washer 7 gives a wider annular gap 6 . the front piece 4 is fixedly mounted on the rear piece 3 by means of a screw 8 which passes through a central hole 4 . 3 in the front piece 4 and , is screwed into a threaded hole 3 . 5 in the rear piece 3 . an alternative design of a cleaning nozzle 11 , which is shown in fig7 - 10 , includes a rear piece 13 and a front piece 14 rotatable mounted on the rear part 13 . the rear piece 13 is provided with a coupling pipe 13 . 1 for the hose on which the cleaning nozzle 11 is to be arranged and showing four symmetrically around its central axis arranged distribution holes 13 . 3 , arranged as in the design described above . the front piece 14 shows a mixing chamber 14 . 1 as in the design described above . the rear piece 13 and the front piece 14 also show corresponding conical surfaces 13 . 4 , 14 . 2 which assembled make the cleaning nozzle exhibiting an annular gap 16 along the periphery of the nozzle which is directed backwards . as in the design described above the width of the annular gap 16 can be regulated by means of a washer 17 . the front piece 14 is rotatable mounted on the rear piece 13 by means of a screw 18 which close to its head shows a cylindrical portion 18 . 1 in the shape of a spindle around which the front piece can rotate . the portion 18 . 1 has a larger diameter and the corresponding hole in the washer 17 and a length permitting a rotation without play which makes the screw 18 to be driven to the rear piece 13 and the washer 17 completely at mounting . the front piece 14 also shows two diametrically , mainly tangentially to an inner circle directed outlet openings 14 . 3 extending in a plane on each side of a diameter plane through the central axis of the cleaning nozzle to in an angle of 5 °- 10 ° to this plane . each outlet opening 14 . 3 is connected to the mixing chamber 14 . 1 by bores 14 . 4 . by forces of reaction from the air exiting from the outlet openings 14 . 3 the front piece 14 is imparted a rotation relative to the rear piece 13 . a friction ring 19 of rubber is arranged in a groove along the periphery of the front piece 14 by means of which the rotation of the front piece 14 can be transmitted to a movement of the complete cleaning nozzle 11 along the inner wall of a duct in an alternative design the outlet openings 14 . 3 and the bores 14 . 4 are replaced by inner open grooves 14 . 5 shown in fig1 , in which the front piece 14 is seen in a direction to its front end . the grooves 14 . 5 extend in the conical surface 14 . 2 at the inner end of the front piece 14 a distance into the mixing chamber 14 . 1 in the front piece 14 and is located in a plane on each side of a diametrical plane through the central axis of the cleaning nozzle in an angle of 5 °- 10 ° to this plane . a part of the front piece 14 in a longitudinal section is shown in fig1 . preferably 6 - 8 grooves are uniformly distributed around the periphery of the front piece 14 . during cleaning of a pipe - shaped ventilation duct , such as is shown in fig1 an exhaust valve for example is replaced with a coupling arrangement 20 as is illustrated in fig1 and 13 . the coupling arrangement 20 presents a flange 21 sealed against a wall and a bent pipe 22 projecting outwardly from the flange to which there is coupled a suction hose which connects the bent pipe to a vacuum cleaner arrangement or the like . the bent pipe 22 shows an insert opening 24 situated in the extension of the centre line to the horizontal portion of the bent pipe 22 in fig1 and 12 , and through the opening is inserted the cleaning nozzle 1 , 11 with the hose 2 . the cleaning operation consists in that the cleaning nozzle 1 , 11 after the insertion in the ventilation duct which is to be cleaned , is fed with compressed air which if desired is fed with a cleaning agent and / or a disinfectant . at high speed compressed air consequently discharges back out from the annular gap along the periphery of the cleaning nozzle 1 , so that the nozzle is driven into the duct as a result of the forces of reaction from the discharging air , and carries the hose 2 with it . simultaneously the suction hose 23 is placed under reduced pressure so that dust which is released from inner walls of the duct is sucked away from the duct and is collected in the vacuum cleaner arrangement which moreover is not shown in the figures . when the cleaning nozzle 1 is brought into the duct it is caused to contact the inner walls of the duct by an action of ejection . by twisting the hose 2 sideways the cleaning nozzle 1 according to the first design mentioned is caused to move sideways in the duct on the same time as it is caused to move ahead in the duct by its own force or eventually also backwards in the duct by pulling the hose . at the use of the cleaning nozzle 1 first scribed above dust and existing deposits are released from inner walls of the duct partly as a result of the cutting effect which is produced by the air discharging from the annular gap 6 , and partly as a result of irregular movements of the cleaning nozzle 1 and impacts against inner walls of the duct . at using the cleaning nozzle 11 in the alternative design the front piece 14 of the cleaning nozzle 11 also is caused to rotate , which movement is transferred into a movement of the entire cleaning nozzle 11 along the walls of the duct . another alternative design of a cleaning nozzle 31 , shown in fig1 - 17 , comprises a rear piece 33 , on which a rotateable front piece 34 is mounted , and an annular gap 36 therebetween . the rear piece 33 is provided with a coupling pipe 33 . 1 for a hose 32 on which the nozzle 31 is proposed to be arranged . this nozzle 31 snows mainly the same design features for the rest as the next above described nozzle . the front piece 34 also shows inner open grooves 34 . 5 extending in an angle to the radial through each groove as in the next above described alternative . however the front piece 34 is arranged rotatably on a shaft 35 by help of two radial ball bearings 38 . 1 and one axial ball bearing 38 . 2 . in order to gain the ejection effect , which is present just at the annular gap 36 , the front piece 34 is provided with an ejector ring 37 running along the annular gap 36 and kept in a distance from the front piece 34 by means of distance means 37 . 1 . the ejector ring 37 and the distance means 37 . 1 can be made in one piece e . g . made of hard rubber , since the ejector ring 37 has the same effect as the friction ring which was mentioned above . the ejector ring 37 also can be made as two concentric rings with distance means them between which facilitates its mounting on the front piece 34 . alternatively the distance means can constitute an integrated portion of the front piece 34 , since the ejector ring can be made completely smooth . a cross section of the ejector ring 37 is shown in fig1 from which it is clear that the outer circumscribed surface 37 . 2 of the ejector ring 37 has an oval profile and its inner surface 37 . 3 has a straight profile . air which is caused to pass the outer surface 37 . 2 of the ejector ring 37 by this is given a higher speed and a lower pressure than the air which is caused to pass through the ejector ring 37 at its inner surface 37 . 3 . when the cleaning nozzle 34 is brought into contact with a wall in a duct this makes that the pressure of the air between the nozzle and the duct wall is lowered further making the cleaning nozzle 34 to contact the duct wall with an increased force compared with the designs described above . the contact of the cleaning nozzle 34 to the wall of the duct is gained more if the nozzle is brought in an angle to the wall . this will be achieved simply by designing the front piece 34 mainly conically tapered from the annular gap 36 to its nose causing the annular gap 36 to remain in the vicinity of the wall . by the projecting ejector ring 37 the desired inclination will be more ensured . an another alternative design of the cleaning nozzle 41 as shown in fig1 - 20 comprises a rear piece 43 on which a rotatable front piece 44 is mounted . the rear piece 43 is connected to a hose 42 . the ejector ring according to the design described above is replaced by a number of grooves 45 extending along the periphery of the front piece 44 in the longitudinal direction of the cleaning nozzle 41 . air which is caused to flow between the inner wall of the duct and the cleaning nozzle is controlled by the grooves 45 in a way which improves the contact of the cleaning nozzle to the wall of the duct . in the figures the grooves 45 are shown extending in a distance from the rear edge of the front piece 44 and forward in a conical portion 44 . 1 directed forward on the front piece . the extension of the grooves 45 in the conical portion 44 . 1 can be varied and also extend along all of this portion . the conical portion 4 . 1 shows a cone angle of a = 15 °, but it can be between 10 °- 40 °. if , as shown in the example , the conical surfaces which lead forwards to the annular gap 6 incline with a gap angle b = 50 ° the air discharging from the annular gap will be directed with an impact angle of 35 ° towards the ceiling surface . the gap angle b can be 30 °- 60 ° by which the impact angle can vary within the region 5 °- 40 °, preferably 10 °- 20 °, by selection of the cone angle a and / or the gap angle b . in order to gain the effect of cleaning nozzles with rotating front pieces more these can be provided with a brush , preferably arranged along the periphery of each front piece , e . g . on the outer side of the ejector ring described above or just at the grooves in the front piece in the alternative design . it is also possible to arrange a circular brush at the nose of the rotating front piece . in order to gain the contact of the cleaning nozzle to the inner wall of a pipe line of a magnetic material , which is most common as pipe lines as a rule are made of galvanized steel sheet , magnets , especially permanent magnets , can be arranged along the periphery of the cleaning nozzle . in that way e . g . the ejector ring described above can show magnet members along its periphery or the rotating nozzle can have such magnets arranged on the , relative to the hose , fixed rear piece or the rotating front piece .