The Ball Valve which came with your Feed Pan will allow you to adjust the flow of raw sap which is being dispensed. You will periodically need to recheck sap depth and adjust the Feed Pan’s rate of flow. The rate of flow is going to fluctuate based on your boiling rate.
A good rule of thumb is to maintain 2” of sap depth in your evaporator pan while you are boiling. This will protect the sap/pan from scorching. Be sure that you are measuring 2” of liquid depth and not 2” of foamy sap. Foam will not protect your evaporator pan the way liquid will. A single drop of vegetable oil will eliminate the foam.