causing considerable loss of head when the powder passes from the powder depositing chamber b to the filter chambers a or c these obstacles oblige the powder which takes part in this transfer to move towards the central axis of the booth and thus towards the parts which move through the booth the fraction of powder which is still charged if electrostatic spray guns are used is redeposited on the parts the ionization compartments e and f further include ionization units 21 23 25 and 27 constituted by insulating tubes extending vertically up the entire height of the booth pins 29 pass through holes in these tubes leaving a space around the pins where they pass through the holes the pins are fixed on the tube along the generatrix that is furthest from the holes by a fixing means such as nailing or the like the pins 29 point towards the centre of the booth perpendicularly to the path followed by the parts and pass through an electrically conductive member which is disposed inside the tube and is connected to the high tension supply the high tension supply is an electrostatic generator which can be the same as that used for the spray guns in module b the pins 29 are thus in contact with the conductive member which brings them to high.