Well I don't really think it's all that interesting. By closing the ball valve all I'm really doing is reducing the VOLUME of water passing over the membrane, not the pressure. What I really want to do is lower my pressure but continue delivering the same volume, mass, of water to be purified. By closing the valve to restrict the volume I'm allowing the drain side to "catch up" with the incoming side, yes it is technically a pressure drop but it's a huge volume loss. Volume and pressure work together. The trick here would be to have a pressure reducing valve, one that allows the same volume of water but has a spring check that closes off incoming water at a certain pressure allowing the same volume to pass through while maintaining the correct pressure. Finding a RPZ style check pressure reducing valve (that works correctly) might prove futile unless searching laboratory products. I wonder if it would be easier to call the city and have them update my water meter to a pressure reducing style?