can you please provide some pictures of what the setup might look like with a valve? I have never used one but I assume ill need to add a small motor to turn on/off the valve depending on when a suction cup is attached. To detect when a suction cup is attached to the surface i use a distance sensor with a range of 2 cm max so it does fairly well at .5 cm.
Ok, After looking from what you said I found the perfect valve for the job:
I think these valves are called ball valves right? I need to get 3 way ones I suppose.
Now the question is what kind of suctions cups/vacuum do I need?