Recently I learned a lot about how pneumatic valves work - or don't work. Originally I had planned to use a 3/2 way valve for the pcknplc machine. This has the advantage that in one switching state I can switch the vacuum through to the pick head and in the other switching state the pressure line to the pick head is vented. 

This is important because otherwise it can happen that the sucked component "sticks" due to the unbalanced negative pressure in the hose line to the pick head. At least that’s the plan. 

But a (dry) test of the valve did not even deliver the satisfactory "click" that is known from relays. After I was pretty frustrated I took the complete valve apart and found the fault. (He sat in front of the valve): These valves work with the help of a pilot valve. This means that the 12V coil or its magnetic field do not move the main valve piston directly but a smaller/lighter piston that uses the air pressure at the pressure connection to control the main valve piston. ⁣

1. I want to switch a negative pressure and not a positive one. As a result, there is no air pressure with which the pilot valve can control the main valve.⁣
2. A certain minimum pressure is required to move the main valve. Otherwise it can happen that the main valve piston is not pushed into the end position and gets stuck in an intermediate position.⁣

In complete: Epic fail, but learned a lot. 🙃😂⁣