Thanks for the reply Fraser. But actually no I can't give you any specs on the valve because I haven't bought and/or built it yet. Phidgetsbc by far is the system that will work the best for my application except for this valve issue so I am trying to design it around the sbc. What is happening here is there will be 6 garden boxes "zones" that will be watered based on the comparative ratio of soil moisture setpoint and actual soil moisture. So to keep the system balanced as zones turn off and on I was going to have a min/max psi setpoint with a 3way mixing valve just past the pump to bypass or add pressure as needed based off a gauge sensor. I could always set the system up as more of a constant volume operation but I was hoping not to have to.