number 1 in fig1 indicates as a whole a machine for molding coloured plastic foam material , such as polypropylene , polyethylene , polystyrene and their copolymers . machine 1 comprises a bin 2 for storing plastic material in the form of pre - expanded granules of given colour ; a known mold 3 ( therefore not described ); and a feed circuit 4 interposed between bin 2 and mold 3 to feed measured amounts of plastic material into mold 3 . more specifically , as shown in fig1 , 2 and 3 , feed circuit 4 comprises a loading reservoir 5 defined by a hollow body 6 coaxial with a longitudinal axis 7 and closed at the top by a lid 8 , and at the bottom by a hopper 9 . reservoir 5 is connected to bin 2 by a feed pipe 10 , the outlet end of which is connected to an inlet 11 on lid 8 by a valve 12 for enabling or disabling material flow to reservoir 5 . reservoir 5 is also connected to a three - inlet fitting 13 fitted to lid 8 and comprising a suction inlet 14 connected by a valve 15 and a pipe 16 to a suction pump 17 , which is activated , when loading reservoir 5 , to create a vacuum inside reservoir 5 and so draw a batch of material into reservoir 5 along pipe 10 and through the open valve 12 . facing inlet 14 , fitting 13 comprises an inlet 18 for compressed air , which is fed along a feed pipe 20 to reservoir 5 by a compressor 19 to bring reservoir 5 , already loaded with a batch of material , to a given operating pressure . compressed - air flow into reservoir 5 is regulated by a valve 21 upstream from inlet 18 and close to the outlet end of pipe 20 . between inlets 14 and 18 , fitting 13 comprises a third inlet connected to a relief valve 22 for discharging the pressure inside reservoir 5 . an intermediate portion of compressed - air feed pipe 20 to reservoir 5 has a branch pipe connected , via an open / close valve 23 , to a number of branches 24 ( only one shown in fig1 for the sake of simplicity ) for feeding compressed air into reservoir 5 through respective inlets 25 , which are formed in a lateral wall of body 6 , are equally spaced about axis 7 , and are located in a plane crosswise to axis 7 and a given distance from hopper 9 . in a variation not shown , pipe 20 has two or more superimposed branch pipes with respective numbers of inlets 25 located in respective planes crosswise to and superimposed along axis 7 . as shown in fig1 to 4 , hopper 9 is funnel - shaped , tapering downwards , with a substantially rectangular outlet 26 , and a substantially circular inlet connected smoothly to the bottom end of body 6 . hopper 9 is closed at the bottom by a block 27 housing a substantially cylindrical header 28 , which is coaxial with an axis 29 perpendicular to axis 7 , communicates with outlet 26 of hopper 9 through an opening 30 parallel to axis 29 , and has a number of lateral outlets 31 , each communicating directly with the inlet of a respective ejector 32 of a group of ejectors 32 carried by block 27 and aligned side by side in a direction parallel to axis 29 . header 28 is controlled by a valve 33 comprising a shutter 34 housed in header 28 and rotating about axis 29 ; and a pneumatic actuator 35 ( fig2 ) fitted to hopper 9 and for moving shutter 34 between an open position ( fig4 ) allowing material to flow freely to ejectors 32 through opening 30 , header 28 , and outlets 31 , and a closed position in which shutter 34 closes outlets 31 to cut off material flow from header 28 to ejectors 32 . as shown in fig1 to 4 , ejectors 32 are pneumatic , and each have inlets for compressed air , which is injected under the control of a valve 36 and intermittently with a given frequency to “ lubricate ” material flow through ejectors 32 . each ejector 32 is connected by a respective material feed pipe 37 to a respective loader 38 ( only one loader 38 shown in the drawings for the sake of simplicity ) defined by a tubular body , which , close to its rear end , has an inlet 39 connected to material feed pipe 37 , and , at its front end , has a nozzle 40 for feeding the incoming material from reservoir 5 directly into mold 3 . loader 38 also comprises a first compressed - air inlet 42 connected by a feed pipe 43 to compressor 19 . an intermediate portion of pipe 43 has a branch pipe fitted with a switch valve 44 connected by a pipe 45 to a second compressed - air inlet 46 close to inlet 42 , and by a pipe 47 to a third compressed - air inlet 48 located at the rear end of loader 38 and communicating with the end of a piston ( not shown ), which is housed inside loader 38 and slid , by the compressed air through inlet 48 , between a withdrawn position opening nozzle 40 , and a forward position closing nozzle 40 . feed circuit 4 also comprises a two - inlet cyclone separator 49 , a first inlet 50 of which is connected by a pipe 51 to a two - way valve 52 fitted to material feed pipe 10 to selectively connect reservoir 5 to bin 2 by pipe 10 , and to cyclone separator 49 by pipe 51 and an end portion of pipe 10 . a second inlet 53 of cyclone separator 49 is connected by a pipe 54 to a first outlet of a two - way valve 55 for connecting pipe 54 to a pipe 56 and , via an open / close valve 57 , to an axial end of header 28 . feed circuit 4 also comprises an aspirator 58 connected by a pipe 59 to a second outlet of valve 55 to communicate , via pipe 56 and valve 57 , with header 28 . operation of machine 1 will now be described with reference to fig5 to 10 , which show a cleaning cycle to which machine 1 is subjected after performing a given number of operating cycles ( in known manner ) using material of a given colour , and after being stopped to make a colour change . the cleaning cycle comprises a first subcycle comprising five steps ; and a second subcycle comprising an end step hereinafter referred to as step 6 . in a preferred embodiment , the first subcycle is repeated two or more times before performing the second subcycle . for the sake of clarity , in fig5 to 10 , the “ active ” portions of feed circuit 4 and the relative travelling directions are indicated , for each step , by continuous lines and directional arrows . step 1 ( fig5 ): suction of the batch of material in reservoir 5 . at this step , valve 12 is opened intermittently ; valve 52 is set to connect cyclone separator 49 to reservoir 5 by pipes 51 and 10 ; valve 23 is opened intermittently ; and , finally , valve 33 is closed , valve 57 is opened , and valve 55 is set to connect header 28 to aspirator 58 . once aspirator 58 is activated , the batch of material in reservoir 5 is sucked into aspirator 58 via header 28 and pipes 56 and 59 . at the same time , compressor 19 ( fig1 ) is activated , and the compressed - air jets blown into reservoir 5 through inlets 25 create an airflow to assist expulsion of the material from reservoir 5 , and , in particular , dislodge into header 28 at least some of the granules of material which , charged electrostatically , would adhere to the inner wall of reservoir 5 ; and the open valve 12 allows airflow from cyclone separator 49 into reservoir 5 to prevent formation of a vacuum inside reservoir 5 . step 2 ( fig6 ): compressed - air injection to remove residue from reservoir 5 . at this step , valve 12 is closed to isolate reservoir 5 from cyclone separator 49 ; valve 23 is kept open intermittently , and valve 21 is opened intermittently to also allow compressed air into reservoir 5 through inlet 18 as well as inlets 25 ; valve 33 is kept closed , valve 57 is kept open , and valve 55 is set to connect header 28 to cyclone separator 49 by pipes 56 and 54 . airflow is thus created through reservoir 5 , along header 28 , and into cyclone separator 49 , and which takes with it any granules of material remaining inside reservoir 5 and header 28 . step 3 ( fig7 ): compressed - air injection to remove residue from the portion of feed circuit 4 feeding material to reservoir 5 . at this step , valve 33 is kept closed ; valve 57 is closed ; valves 23 and 21 are kept open intermittently , and valve 12 is opened ; and valve 52 is set to connect reservoir 5 to cyclone separator 49 by pipes 10 and 51 . airflow is thus created through reservoir 5 , out of reservoir 5 through material inlet 11 , along pipes 10 and 51 , and into cyclone separator 49 , taking with it any granules still left inside reservoir 5 and pipe 10 . step 4 ( fig8 ): compressed - air injection to remove residue from the portion of feed circuit 4 feeding material to loaders 38 . at this step , valves 12 and 21 are closed ; valve 57 is opened ; valve 55 is set to connect header 28 to cyclone separator 49 ; valve 33 is opened to also connect header 28 to loaders 38 by respective ejectors 32 and pipes 37 ; and valves 44 are set so that , for each loader 38 , compressed air fed along pipe 43 flows into loader 38 through inlet 42 , and compressed air fed along pipe 47 flows into loader 38 through inlet 48 to move the piston ( not shown ) into the forward position closing nozzle 40 . for each loader 38 , operation of compressor 19 ( fig1 ) thus creates airflow through loader 38 via inlets 42 and 39 , along respective pipe 37 , and through respective ejector 32 into header 28 , where it joins with the airflow fed through inlets 25 into reservoir 5 , and flows out along pipes 56 and 54 into cyclone separator 49 . any granules left on the material feed portions of loaders 38 , pipes 37 , and ejectors 32 are thus removed . step 5 ( fig9 ): suction to remove residue from the portion of feed circuit 4 feeding material to loaders 38 . this step differs from step 4 by setting valve 55 to connect header 28 to aspirator 58 as opposed to cyclone separator 49 , so that the blow - off airflow produced by compressor 19 ( fig1 ) along pipes 20 and 43 flows along part of reservoir 5 , loaders 38 , pipes 37 , and ejectors 32 into header 28 , and is sucked out by aspirator 58 . this step provides for removing from feed circuit 4 any remaining granules fed into header 28 at steps 1 to 4 described above . step 6 ( fig1 ): “ no - load ” air run of loaders 38 . at this step , operation of loaders 38 is simulated by feeding them with air , which is fed through inlets 25 and , after first opening valve 21 , through inlet 18 into reservoir 5 , and flows into loaders 38 through left - open valve 33 , header 28 , ejectors 32 and respective pipes 37 , following the same path as the actual material . valve 36 for feeding air through ejectors 32 is opened intermittently , and valves 44 are set so that , for each loader 38 , compressed air flows along pipes 43 and 45 ; and cut - off of air supply to inlet 48 moves the piston ( not shown ) back to the withdrawn position opening nozzle 40 . the compressed air injected into loader 38 through inlets 42 and 46 creates a venturi effect inside loader 38 , which expels the air “ batch ” through nozzle 40 , thus removing any granules from the front area of loader 38 close to nozzle 40 . in a variation not shown , the cleaning cycle comprises a further step ( not shown ) before or simultaneously with step 4 described above . the further step comprises blowing an antistatic product into reservoir 5 , together with the air fed through inlets 25 , to counteract the tendency of the granules to adhere to the inner wall of reservoir 5 , and so assist dislodging the granules into header 28 .