Recirculating Problem
It was recently noticed by our team that after the loading state had switched to the settling state, a slow but seemingly never-ending recirculation of particles was occurring in the settling column. It was hypothesized that this could have been a result of the elbow connections, the change in diameter tubing from the flocculator to the settling column, the valve shutoff, upflow versus downflow through the column, or the abrupt stopping of the pumps in the transition of states. All of these ideas were put to the test in simple visual experiments.
First, the pump controll shutoff was removed from the beginning of the settle state to a new state before settle state. This allowed for the pumps to be shutoff seconds before the valves were shutoff. Different times between the two shutoff points were experimented with, but each time, at the time of the valve shutoff, a jerk in motion would seem to cause a recirculation in flow.
Monroe programmed a new variable in Process Controller to ramp down the pump controls to zero instead of abruptly switching from a high pump control value to zero (shutoff) automatically. We installed this ramp down function in Process Controller and tested it on our apparatus. The ramp down would bring the flow down to an easier flow.