I am trying to develop an control system for a pressure test system. The system needs to perform one of two functions, control the pressure or control the bleed down rate. My system consists of a air driven water pump and multiple "zones" that are pressurized by this one pump. It should also be noted that each zone is temperature controlled and therefore pressure will change due to changing temperatures. Each zone needs to have its own pressure control.
Each zone consists of a air-operated shut-in valve and motorized metering valve on the inlet to the zone and the outlet. The plan is to use the inlet metering valve to control the pressure increase and and the outlet metering valve to control the pressure decrease. The metering valves do not seal 100% so the shut-in valves are required to hold at pressure.
So what I am looking for is some suggestions on how I set the PID controls up for the inlet and outlet metering valves so they are not both trying to control at the same time?
The way the metering valve are made is basically a motor turning a needle valve. Therefore the reaction time is slow compared to the pressure increase. Is what I am doing going to be possible?