After mashing it's time to direct the mash flow into the boiler. The flow rate is equal to the total wort you want to collect divided by ninety minutes. In my case 13.5 gal per 90 minutes or 3 quarts per 5 minutes. To obtain this low rate with a 1/2 inch ball valve, it is almost entirely closed. Occasionally a piece of grain will get past the false bottom and obstruct the small opening in the valve. If you're monitoring the run-off it's a simple matter to quickly open the valve to clear it, then close it back down.
I'm hoping the gizmo in the picture will automatically clear itself of any grain fragments and maintain the desired flow. It uses a spring under tension that pushes a ball bearing into the inside opening of the inlet. When the tension is adjusted for the desired flow, the inlet pressure will settle at a value just high enough to counteract the spring tension. If a piece of grain restricts the flow the inlet pressure will rise. The pressure rise will push harder on the bearing, therefore increasing the opening and allowing the grain to pass. Once cleared it should settle back to maintain the flow rate. I hope!