Pneumatic manual valve v2

This valve can be used to control pneumatic cylinders manually. It is a remake of [thing:2932081](https://www.thingiverse.com/thing:2932081). The valve system is the same, but it now features proper pneumatic connections (4mm with lock or M5) and it can be mounted on a manifold base. The symmetric version allows mounting stuff on two sides for more complex pneumatic logic circuits.

Knobs need supports; take care that air hole is clear. Alternatingly use Knob and Knob2 to avoid knob collisions when used in-line. Use a long M3 bolt with your favourite fastener (I use one or two lock nuts) to mount the knob, and one or two short M2 screws as endstops if desired. Photographed knobs look slightly different from STL's due to design changes to make orientation flexible.

Use the [Parametric manifold base](https://www.thingiverse.com/thing:3202156) to generate manifold bases with any number of ports, single-sided or double-sided. Connectors are available in the [Non-return valve](https://