In the present article the experimental test results of air distribution with one and several diffusers. positioned at different distances on the axis of a circular duct made of oilcloth, are shown. The velocity profiles are obtained by measuring continously at different distances from the holes and presented in non dimensional form. These figures show the trend of the flow for different hole diameters and for different distances among the nozzles; a figure relating the pressure trend is also shown. The figures allow to generalize the obtained results. The tests show the merging effect for several jets, under isothermal conditions. Experimental results have been compared with others from literature.