I usually do not mix herbicides and fertilizers with the exception of soil active products such as Preemergents, simazine and Image. My postemergent and preemergent applications are applied at 40 PSI measured and regulated at the hand piece. Straight fertilizers, insecticides and fungicides are applied at up to 150 PSI. I am not guessing the pressure at the end of the hose. I wish I were 5'9" and 150 lbs. All of my life I have had people treat me as if I am some kind of invalid. Even new customers get the idea that I am going to be sending a crew of people to do the work. Then they see me hiking up and down their lawn with the engine driven backpack or lifting 50 lb bags of fertilizers over my head to get them in the skid tank. You are right about people. I have had average to big people tell me that the backpack sprayer is so heavy and they do not know how I do it. Much less keep up all day long.