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.

 

Size matters. How big of a system are you looking for? What stroke, what speed, what force, and what positional repeatability?

Rather than me name brand names, you can google "used hydraulic" and "used servovalve" to find lower cost valves and cylinders.

If this is just an unloaded demo: Least expensive route is to go pneumatic. Components are cheaper and if you have shop air you avoid the cost of a hydraulic power unit. There are companies that make pneumatic servovalves and there are direct drive hydraulic proportional valves that work very well with pneumatics. For hydraulic valves used with air, after use, rinse out the valve with alcohol to avoid rust. An additional advantage is there are magnetostrictive feedback devices with analog outputs (volts or 4 to 20 mA) that mount right onto alumiminum body air cylinders (get a cylinder with square extruded body -not round type)and sense the position of a magnet you attach to the piston inside. Otherwise, you can get hydraulic or pneumatic cylinders machined to accept internal magnetostrictive probes. (Watch the spelling, it is NOT magnetoREstrictive -leave out the "RE". they are also called LDT's but that is a more general term.)

Lowest cost closest loop controls are small cigarette pack size PID modules that mount to DIN rails. These are NOT "motion controllers". these are devices that you can connect a potentiometer to for command, and an analog probe (such as mentioned above) for feedback, but digitally enter the P, I, and D gains.

If this is a studetn demo, a fun thing to do is get tow air cylinders, equip both with analog feedback devices, but only connect one to a pneumatic proportional or servovalve. The other one serves as your command source. Just pull the rod in and out on the command source cylinder (ports open to atmosphere), and watch the powered one match your motion.

I may be blocked if i mention manufacturers or part numbers, so google "PID module", "magnetostrictive probe" or "LDT" (not to be confused with LVDT -completley different). Those are industry wide terms -not unique products.

Twenty years ago I designed and tested hydraulic servoactuators and pneumatic servoactuators for a large corporation. I'm still familair with that business, but work on bigger systems now. I can provide multiple brand names for you explore, and some good used equipment dealers -but I don't think it's allowed on this forum.

One more thought for best bang for the buck -check out your local used equipment warehouses. The places that sell everything from furniture to stamping presses.

Good luck. Let us know what you come up with.