the inside diameter d 6 of each nozzle is typically between about 30 and 70 mm and each nozzle extends into head 15 a distance of between about 100 and 300 mm the ratio d 6 d 1 between the inside diameter of each nozzle and the diameter of vessel 1 is typically between about 0 008 and 0 020 the angled orientation of nozzles 19 serves to impart a moderate degree of beneficial circular or swirling motion to the pulp during withdrawal through outlet 17 nozzles 19 are preferably installed in one or more circular patterns concentric with the axis of vessel 1 wherein the nozzles on a given circular pattern are equally spaced on the pattern at least eight nozzles are generally preferred but any reasonable number may be installed as needed typically 16 nozzles are installed in two circular patterns as illustrated in fig1 nozzles 19 are oriented relative to head 15 as illustrated in fig2 and section 4 4 is presented in fig4 angle a 2 is between about 25 and 65 degrees preferably about 45 degrees as measured between tangent 25 and axis 21 of specific nozzle 23 tangent 25 is a line drawn tangent to the circle formed by the circular pattern at the location of nozzle 23 or more specifically at the intersection 27.