the chamber 6 but no appreciable pressure differential within the chamber that is the blade does not induce fiber flow from the leading toward the trailing end of the chamber rather fiber flow is induced and controlled by the centrifugal fan 10 which draws a vacuum on the chamber through adjustable orifice plate 8 and discharge orifice 9 the rate of flow of the fibers and their retention within the fiberizing zone 33 may be controlled by adjusting the cover 31 of air inlet 30 with the size of the fiberizing zone and hence retention time additionally controlled by the adjustment of the location of orifice plate 8 these adjustments will be empirical consistent with the objectives of securing maximum fiber separation while minimizing fiber damage and knot formation with the arrangement just described fiber flow is induced and controlled independently of the action of the fiberizing blade 7 and results in a favorable vortex placement around the fiberizing blade plane in fact the fiberizing blade may be used to produce a slight pressure differential in the direction opposite to the direction of fiber flow to further enhance the vortex action in the plane of the fiberizing blade the extent of fiber separation which occurs in the first stage unit 1 will depend upon the nature of the fibers being separated and the manner in which they were treated in some instances wholly adequate separation for a given purpose may be achieved in the first stage however where the fibers have been impregnated with wet strength resins second and third stage fiberization is usually required to effect substantially complete fiber separation as in the case of.