Please excuse my ignorance but I'm new to robotics.
When using a pneumatic power source, how is it controlled, is it only possible to control air flow by pulsing solenoids or is there some kind of variable valve (more like a tap), that's available?

If an electro-pneumatic tap like valve (that can deliver smooth flow control) is available, could anyone point me to a source of them please?

Many thanks for any help that anyone can provide.

Trev