Adjust the injector to the reading of a vac gauge. When the ladder is flooded the vac will drop off, if you open the injector too much the vac drops off. When you reach your highest vac level during peak flow you have the injector set perfectly and will have the best vac transfer you can possible achieve.
Injectors actually increase vac levels. On my system with 8 injectors and 8 ladders I have less than 0.15 CFM of injected air. Simple to install and cost under $10 at the local hardware store. In 2013 half our taps were laddered and we did .47 g/tap of syrup. This season 800+ of 1100 will be thru at least one ladder and most thru at least two ladders.
Our system has had ladders since the late 1970's to bring those Vermont trees the the NY sugar house.... amazing how 185 feet makes syrup sell differently!