###Valves  Here is a low pressure air valve, salvaged from an electric-action pipe organ.  Here is a [solenoid valve](https://www.amazon.com/gp/product/B00ON8XFSO/ref=ppx_yo_dt_b_asin_title_o01__o00_s00?ie=UTF8&psc=1). Operates at 12V ~0.5Amps. Up to 140 psi. about $10 from Amazon. Other similar products are available, in other ranges for flow and pressure.  Here is a cheap and quick way to make a valve for liquid or gas flowing in a flexible tube. Uses a gear motor to provide enough torque to clamp shut a tube. Needs some work to make it reliable - for instance, a way to determine when it has done its job of closing off the tube.