wall by aligning the proper gradation marking 47 to the reference circle 48 for each of the weir plates the radial position of each of the weir plates on the head wall may be precisely positioned at a uniform radial distance from the axis of the bowl as shown in fig3 and 4 the discharge clarified liquid e g u201c centrate u201d flows through the channel 20 in the bowl towards the head wall 60 and through drain openings 50 arranged annularly in the head wall 60 these openings 50 are preferably arranged in a circle on the head wall wherein the circle of openings is centered on the rotational axis of the bowl the gap g 54 between the weir plate 28 and choke plate 44 defines a passage for the centrate flowing to the discharge casing 36 the flow 51 of centrate is generally axially as the centrate moves through the channel 20 and into the opening 50 of the head wall because of centrifugal force the flow 51 quickly turns radially outward as the centrate flows over the edge of the channel 31 on the weir plate 44 and enters the gap 54 between the weir plate and the choke plate the centrate flows 51 radial outward through the gap 54 and into the centrate discharge casing 36 the choke plates 44 are mounted on the shaft 64 fig3 of the bowl or screw conveyor the choke plate includes a collar 77 that engages the shaft an upper surface of the collar supports a ball bearing assembly 66 which provides an engagement between the choke plate and a non rotating axial adjustment mechanism 75 this adjustment mechanism 75 is supported by.