OK, looking for opinions here. Let's say I am trying to maintain a constant pressure or tank level using 3 pumps with VFD's. Now instead of buying a PID controller I split the pressure reading to all 3 drives and let their internal PID's do the work. I will have some sort of setpoint controller telling the pumps when to turn off in a lead/lag/laglag fashion. Do you think it would be possible to tune the 3 drives so they will run smoothly, or would it be an erratic mess? Say pump 1 is churning along at full speed and can't keep up with demand. The setpoint controller says OK I need another pump. It kicks on lag and now the lag's PID is telling it to ramp up while the lead PID sees the change and tells it to ramp down... when pressure starts to get close to setpoint what's gonna happen? Could I just pump enough I or D into them to keep them from changing too fast (assuming dependent gains PID)? Or is this just a bad idea and we should buy a PID controller to give all pumps the same speed reference?