A system, an apparatus and a method for adjusting a weir control the rate and/or speed at which drilling fluid feeds a separator. Multiple separators are typically used in parallel to process fluid returning from the well. A distribution manifold directs fluid to each separator. The weir is positioned within a feeder on an inlet end of the separator and connects to an attachment plate within the feeder. The distribution manifold or other flow control mechanism operates in combination with the weir. Adjustment apparatuses control the height of the weir to determine the rate the fluid flows onto the separator. The adjustment apparatuses provide mechanical and/or automated operation of the weir. Various profiles of the weir and adjustments of the height of the weir within the feeder increase and/or decrease the speed of the fluid as the fluid spills into the separator.