This shut-off valve can be assembled within one second. Place the knob in the housing, stick the 4 mm pneumatic tube through the hole and it is ready.
Rotating the knob creates two kinks in the tube, effectively shutting off the airflow. These kinks may still be visible after opening the valve depending on the shutoff duration and tube material properties. I do not know how many operations are possible on the same spot before the tube gets damaged, but we will see. Of course the tube can always be shifted to different positions when the valve is open.
If the standard knob does not lock well due to too flexible tubes (e.g. Festo PUN-H), use the Knob_Tight version instead.
An important advantage of this valve is that it is leak-free. This is ideal for shutting of pressurized air tanks for extended periods without losing pressure.
Tested with 4 mm polyurethane tubes from CompatiblePneumatics with standard knob, and Festo PUN-H 4x0,75 mm with Knob_Tight.