Two materials technicians here; In our spare time we use the lab facilities at our University to build DIY kits such as CNC machines, hydraulic pumps, engine rebuilds, generator rebuilds etc. We are now proficient in Machining (CNC and Manual), electronics (building boards and drivers etc.) and hydraulics. We know little of Servo Hydraulic valves and control (PID) systems. Can anyone give use any useful info on servo-valves, where to buy them (cheaply) and how to match them to a suitable control system.